Programs & Examples On #Python

Python is a dynamic, strongly typed, object-oriented, multipurpose programming language, designed to be quick (to learn, to use, and to understand), and to enforce a clean and uniform syntax. Two similar but incompatible versions of Python are in use (Python 2.7 or 3.x). For version-specific Python questions, please also use the [tag:python-2.7] or [tag:python-3.x] tags. When using a Python variant (i.e Jython, Pypy, etc.) - please also tag the variant.

How do you create different variable names while in a loop?

I think the challenge here is not to call upon global()

I would personally define a list for your (dynamic) variables to be held and then append to it within a for loop. Then use a separate for loop to view each entry or even execute other operations.

Here is an example - I have a number of network switches (say between 2 and 8) at various BRanches. Now I need to ensure I have a way to determining how many switches are available (or alive - ping test) at any given branch and then perform some operations on them.

Here is my code:

import requests
import sys

def switch_name(branchNum):
    # s is an empty list to start with
    s = []
    #this FOR loop is purely for creating and storing the dynamic variable names in s
    for x in range(1,8,+1):
        s.append("BR" + str(branchNum) + "SW0" + str(x))

    #this FOR loop is used to read each of the switch in list s and perform operations on
    for i in s:
        # other operations can be executed here too for each switch (i) - like SSH in using paramiko and changing switch interface VLAN etc.

def main():  

    # for example's sake - hard coding the site code
    branchNum= "123"

if __name__ == '__main__':

Output is:








Writing string to a file on a new line every time

If you use it extensively (a lot of written lines), you can subclass 'file':

class cfile(file):
    #subclass file to have a more convienient use of writeline
    def __init__(self, name, mode = 'r'):
        self = file.__init__(self, name, mode)

    def wl(self, string):
        self.writelines(string + '\n')

Now it offers an additional function wl that does what you want:

fid = cfile('filename.txt', 'w')
fid.wl('appends newline charachter')
fid.wl('is written on a new line')

Maybe I am missing something like different newline characters (\n, \r, ...) or that the last line is also terminated with a newline, but it works for me.

Changing user agent on urllib2.urlopen

I answered a similar question a couple weeks ago.

There is example code in that question, but basically you can do something like this: (Note the capitalization of User-Agent as of RFC 2616, section 14.43.)

opener = urllib2.build_opener()
opener.addheaders = [('User-Agent', 'Mozilla/5.0')]
response ='')

Removing index column in pandas when reading a csv

One thing that i do is df=df.reset_index() then df=df.drop(['index'],axis=1)

How to len(generator())

Generators have no length, they aren't collections after all.

Generators are functions with a internal state (and fancy syntax). You can repeatedly call them to get a sequence of values, so you can use them in loop. But they don't contain any elements, so asking for the length of a generator is like asking for the length of a function.

if functions in Python are objects, couldn't I assign the length to a variable of this object that would be accessible to the new generator?

Functions are objects, but you cannot assign new attributes to them. The reason is probably to keep such a basic object as efficient as possible.

You can however simply return (generator, length) pairs from your functions or wrap the generator in a simple object like this:

class GeneratorLen(object):
    def __init__(self, gen, length):
        self.gen = gen
        self.length = length

    def __len__(self): 
        return self.length

    def __iter__(self):
        return self.gen

g = some_generator()
h = GeneratorLen(g, 1)
print len(h), list(h)

How to install pip3 on Windows?

For python3.5.3, pip3 is also installed when you install python. When you install it you may not select the add to path. Then you can find where the pip3 located and add it to path manually.

How to multiply all integers inside list

#multiplying each element in the list and adding it into an empty list
original = [1, 2, 3]
results = []
for num in original:
    results.append(num*2)# multiply each iterative number by 2 and add it to the empty list.


correct way to define class variables in Python

Neither way is necessarily correct or incorrect, they are just two different kinds of class elements:

  • Elements outside the __init__ method are static elements; they belong to the class.
  • Elements inside the __init__ method are elements of the object (self); they don't belong to the class.

You'll see it more clearly with some code:

class MyClass:
    static_elem = 123

    def __init__(self):
        self.object_elem = 456

c1 = MyClass()
c2 = MyClass()

# Initial values of both elements
>>> print c1.static_elem, c1.object_elem 
123 456
>>> print c2.static_elem, c2.object_elem
123 456

# Nothing new so far ...

# Let's try changing the static element
MyClass.static_elem = 999

>>> print c1.static_elem, c1.object_elem
999 456
>>> print c2.static_elem, c2.object_elem
999 456

# Now, let's try changing the object element
c1.object_elem = 888

>>> print c1.static_elem, c1.object_elem
999 888
>>> print c2.static_elem, c2.object_elem
999 456

As you can see, when we changed the class element, it changed for both objects. But, when we changed the object element, the other object remained unchanged.

Cannot kill Python script with Ctrl-C

KeyboardInterrupt and signals are only seen by the process (ie the main thread)... Have a look at Ctrl-c i.e. KeyboardInterrupt to kill threads in python

How do I print the content of a .txt file in Python?

This will give you the contents of a file separated, line-by-line in a list:

with open('xyz.txt') as f_obj:

Python Array with String Indices

Even better, try an OrderedDict (assuming you want something like a list). Closer to a list than a regular dict since the keys have an order just like list elements have an order. With a regular dict, the keys have an arbitrary order.

Note that this is available in Python 3 and 2.7. If you want to use with an earlier version of Python you can find installable modules to do that.

How to find whether a number belongs to a particular range in Python?

No, you can't do that. range() expects integer arguments. If you want to know if x is inside this range try some form of this:

print 0.0 <= x <= 0.5

Be careful with your upper limit. If you use range() it is excluded (range(0, 5) does not include 5!)

Is it possible to have multiple statements in a python lambda expression?

A Hacky way to combine multiple statements into a single statement in python is to use the "and" keyword as a short-circuit operator. Then you can use this single statement directly as part of the lambda expression.

This is similar to using "&&" as the short-circuit operator in shell languages such as bash.

Also note: You can always fix a function statement to return a true value by wrapping the function.


def p2(*args):
    return 1 # a true value

junky = lambda x, y: p2('hi') and p2('there') and p2(x) and p2(y)

junky("a", "b")

On second thought, its probably better to use 'or' instead of 'and' since many functions return '0' or None on success. Then you can get rid of the wrapper function in the above example:

junky = lambda x, y: print('hi') or print('there') or print(x) or print(y)

junky("a", "b")

'and' operate will evaluate the expressions until it gets to the first zero return value. after which it short-circuits. 1 and 1 and 0 and 1 evaluates: 1 and 1 and 0, and drops 1

'or' operate will evaluate the expressions until it gets to the first non-zero return value. after which it short-circuits.

0 or 0 or 1 or 0 evaluates 0 or 0 or 1, and drops 0

How to find list intersection?

If order is not important and you don't need to worry about duplicates then you can use set intersection:

>>> a = [1,2,3,4,5]
>>> b = [1,3,5,6]
>>> list(set(a) & set(b))
[1, 3, 5]

Counting lines, words, and characters within a text file using Python

One of the way I like is this one , but may be good for small files

with open(fileName,'r') as content_file:
    content =
    lineCount = len(re.split("\n",content))
    words = re.split("\W+",content.lower())

To count words, there is two way, if you don't care about repetition you can just do

words_count = len(words)

if you want the counts of each word you can just do

import collections
words_count = collections.Counter(words) #Count the occurrence of each word

python-pandas and databases like mysql

For Postgres users

import psycopg2
import pandas as pd

conn = psycopg2.connect("database='datawarehouse' user='user1' host='localhost' password='uberdba'")

customers = 'select * from customers'

customers_df = pd.read_sql(customers,conn)


Access IP Camera in Python OpenCV

To access an Ip Camera, first, I recommend you to install it like you are going to use for the standard application, without any code, using normal software.

After this, you have to know that for different cameras, we have different codes. There is a website where you can see what code you can use to access them:

But be careful, for my camera (Intelbras S3020) it does not work. The right way is to ask the company of your camera, and if they are a good company they will provide it.

When you know your code just add it like:

cap = cv2.VideoCapture("http://LOGIN:PASSWORD@IP/cgi-bin/mjpg/video.cgi?&subtype=1")

Instead LOGIN you will put your login, and instead PASSWORD you will put your password.

To find out camera's IP address there is many softwares that you can download and provide the Ip address to you. I use the software from Intelbras, but I also recommend EseeCloud because they work for almost all cameras that I've bought:

In this example, it shows the protocol http to access the Ip camera, but you can also use rstp, it depends on the camera, as I said.

If you have any further questions just let me know.

Remove the first character of a string

deleting a char:

def del_char(string, indexes):

    'deletes all the indexes from the string and returns the new one'

    return ''.join((char for idx, char in enumerate(string) if idx not in indexes))

it deletes all the chars that are in indexes; you can use it in your case with del_char(your_string, [0])

How can I convert an RGB image into grayscale in Python?

The fastest and current way is to use Pillow, installed via pip install Pillow.

The code is then:

from PIL import Image
img ='input_file.jpg').convert('L')'output_file.jpg')

Python Linked List

Expanding Nick Stinemates's answer

class Node(object):
    def __init__(self): = None = None

class LinkedList:
    def __init__(self):
        self.head = None

    def prepend_node(self, data):
        new_node = Node() = data = self.head
        self.head = new_node

    def append_node(self, data):
        new_node = Node() = data
        current = self.head
            current = = new_node

    def reverse(self):
        """ In-place reversal, modifies exiting list"""
        previous = None
        current_node = self.head

        while current_node:
            temp =
   = previous
            previous = current_node
            current_node = temp
        self.head = previous

    def search(self, data):
        current_node = self.head
            while != data:
                current_node =
            return True
            return False

    def display(self):
        if self.head is None:
            print("Linked list is empty")
            current_node = self.head
            while current_node:
                current_node =

    def list_length(self):
        list_length = 0
        current_node = self.head
        while current_node:
            list_length += 1
            current_node =
        return list_length

def main():
    linked_list = LinkedList()

    print("Lenght of singly linked list is: " + str(linked_list.list_length()))

if __name__ == "__main__":

How to convert a PIL Image into a numpy array?

If your image is stored in a Blob format (i.e. in a database) you can use the same technique explained by Billal Begueradj to convert your image from Blobs to a byte array.

In my case, I needed my images where stored in a blob column in a db table:

def select_all_X_values(conn):
    cur = conn.cursor()
    cur.execute("SELECT ImageData from PiecesTable")    
    rows = cur.fetchall()    
    return rows

I then created a helper function to change my dataset into np.array:

X_dataset = select_all_X_values(conn)
imagesList = convertToByteIO(np.array(X_dataset))

def convertToByteIO(imagesArray):
    # Converts an array of images into an array of Bytes
    imagesList = []

    for i in range(len(imagesArray)):  
        img =[i])).convert("RGB")
        imagesList.insert(i, np.array(img))

    return imagesList

After this, I was able to use the byteArrays in my Neural Network.


How to check if a value exists in a dictionary (python)

Python dictionary has get(key) function

>>> d.get(key)

For Example,

>>> d = {'1': 'one', '3': 'three', '2': 'two', '5': 'five', '4': 'four'}
>>> d.get('3')
>>> d.get('10')

If your key does'nt exist, will return None value.

foo = d[key] # raise error if key doesn't exist
foo = d.get(key) # return None if key doesn't exist

Content relevant to versions less than 3.0 and greater than 5.0.


How do I pass a string into subprocess.Popen (using the stdin argument)?

p = Popen(['grep', 'f'], stdout=PIPE, stdin=PIPE, stderr=STDOUT)    
testresult = p.communicate()[0]

Error: Segmentation fault (core dumped)

There is one more reason for such failure which I came to know when mine failed

  • You might be working with a lot of data and your RAM is full

This might not apply in this case but it also throws the same error and since this question comes up on top for this error, I have added this answer here.

Why does "pip install" inside Python raise a SyntaxError?

To run pip in Python 3.x, just follow the instructions on Python's page: Installing Python Modules.

python -m pip install SomePackage

Note that this is run from the command line and not the python shell (the reason for syntax error in the original question).

Subtracting two lists in Python

list(set([x for x in a if x not in b]))
  • Leaves a and b untouched.
  • Is a unique set of "a - b".
  • Done.

How to write string literals in python without having to escape them?

Raw string literals:

>>> r'abc\dev\t'

binning data in python with scipy/numpy

Another alternative is to use the This method applies in-place a desired operation at specified indices. We can get the bin position for each datapoint using the searchsorted method. Then we can use at to increment by 1 the position of histogram at the index given by bin_indexes, every time we encounter an index at bin_indexes.

data = np.random.random(100) * 100
bins = np.linspace(0, 100, 10)

histogram = np.zeros_like(bins)

bin_indexes = np.searchsorted(bins, data), bin_indexes, 1)

Updating Python on Mac

First, install Homebrew (The missing package manager for macOS) if you haven': Type this in your terminal

/usr/bin/ruby -e "$(curl -fsSL"

Now you can update your Python to python 3 by this command
brew install python3 && cp /usr/local/bin/python3 /usr/local/bin/python

Python 2 and python 3 can coexist so to open python 3, type python3 instead of python

That's the easiest and the best way.

Python Variable Declaration

Variables have scope, so yes it is appropriate to have variables that are specific to your function. You don't always have to be explicit about their definition; usually you can just use them. Only if you want to do something specific to the type of the variable, like append for a list, do you need to define them before you start using them. Typical example of this.

list = []
for i in stuff:

By the way, this is not really a good way to setup the list. It would be better to say:

list = [i for i in stuff] # list comprehension

...but I digress.

Your other question. The custom object should be a class itself.

class CustomObject(): # always capitalize the class name...this is not syntax, just style.
customObj = CustomObject()

How to find tags with only certain attributes - BeautifulSoup

You can use lambda functions in findAll as explained in documentation. So that in your case to search for td tag with only valign = "top" use following:

td_tag_list = soup.findAll(
                lambda == "td" and
                len(tag.attrs) == 1 and
                tag["valign"] == "top")

Find all CSV files in a directory using Python

By using the combination of filters and lambda, you can easily filter out csv files in given folder.

import os

files = os.listdir("/path-to-dir")    
files = list(filter(lambda f: f.endswith('.csv'), files))

# lambda returns True if filename name ends with .csv or else False
# and filter function uses the returned boolean value to filter .csv files from list files.

Python handling socket.error: [Errno 104] Connection reset by peer

"Connection reset by peer" is the TCP/IP equivalent of slamming the phone back on the hook. It's more polite than merely not replying, leaving one hanging. But it's not the FIN-ACK expected of the truly polite TCP/IP converseur. (From other SO answer)

So you can't do anything about it, it is the issue of the server.

But you could use try .. except block to handle that exception:

from socket import error as SocketError
import errno

    response = urllib2.urlopen(request).read()
except SocketError as e:
    if e.errno != errno.ECONNRESET:
        raise # Not error we are looking for
    pass # Handle error here.

Single Line Nested For Loops

You might be interested in itertools.product, which returns an iterable yielding tuples of values from all the iterables you pass it. That is, itertools.product(A, B) yields all values of the form (a, b), where the a values come from A and the b values come from B. For example:

import itertools

A = [50, 60, 70]
B = [0.1, 0.2, 0.3, 0.4]

print [a + b for a, b in itertools.product(A, B)]

This prints:

[50.1, 50.2, 50.3, 50.4, 60.1, 60.2, 60.3, 60.4, 70.1, 70.2, 70.3, 70.4]

Notice how the final argument passed to itertools.product is the "inner" one. Generally, itertools.product(a0, a1, ... an) is equal to [(i0, i1, ... in) for in in an for in-1 in an-1 ... for i0 in a0]

Iterating over dictionaries using 'for' loops

key is just a variable name.

for key in d:

will simply loop over the keys in the dictionary, rather than the keys and values. To loop over both key and value you can use the following:

For Python 3.x:

for key, value in d.items():

For Python 2.x:

for key, value in d.iteritems():

To test for yourself, change the word key to poop.

In Python 3.x, iteritems() was replaced with simply items(), which returns a set-like view backed by the dict, like iteritems() but even better. This is also available in 2.7 as viewitems().

The operation items() will work for both 2 and 3, but in 2 it will return a list of the dictionary's (key, value) pairs, which will not reflect changes to the dict that happen after the items() call. If you want the 2.x behavior in 3.x, you can call list(d.items()).

Is there a function in python to split a word into a list?

The easiest option is to just use the list() command. However, if you don't want to use it or it dose not work for some bazaar reason, you can always use this method.

word = 'foo'
splitWord = []

for letter in word:

print(splitWord) #prints ['f', 'o', 'o']

Selenium: WebDriverException:Chrome failed to start: crashed as google-chrome is no longer running so ChromeDriver is assuming that Chrome has crashed

I encountered the exact problem running on docker container (in build environment). After ssh into the container, I tried running the test manually and still encountered

(unknown error: DevToolsActivePort file doesn't exist)
     (The process started from chrome location /usr/bin/google-chrome-stable is 
      no longer running, so ChromeDriver is assuming that Chrome has crashed.)

When I tried running chrome locally /usr/bin/google-chrome-stable, error message

Running as root without --no-sandbox is not supported

I checked my ChromeOptions and it was missing --no-sandbox, which is why it couldn't spawn chrome.

capabilities =
  chromeOptions: { args: %w(headless --no-sandbox disable-gpu window-size=1920,1080) }

PyTorch: How to get the shape of a Tensor as a list of int

If you're a fan of NumPyish syntax, then there's tensor.shape.

In [3]: ar = torch.rand(3, 3)

In [4]: ar.shape
Out[4]: torch.Size([3, 3])

# method-1
In [7]: list(ar.shape)
Out[7]: [3, 3]

# method-2
In [8]: [*ar.shape]
Out[8]: [3, 3]

# method-3
In [9]: [*ar.size()]
Out[9]: [3, 3]

P.S.: Note that tensor.shape is an alias to tensor.size(), though tensor.shape is an attribute of the tensor in question whereas tensor.size() is a function.

Add to python path mac os x

Mathew's answer works for the terminal python shell, but it didn't work for IDLE shell in my case because many versions of python existed before I replaced them all with Python2.7.7. How I solved the problem with IDLE.

  1. In terminal, cd /Applications/Python\ 2.7/
  2. then sudo nano, enter password if required.
  3. after os.chdir(os.path.expanduser('~/Documents')) this line, I added sys.path.append("/Users/admin/Downloads....") NOTE: replace contents of the quotes with the directory where python module to be added
  4. to save the change, ctrl+x and enter Now open idle and try to import the python module, no error for me!!!

Python's "in" set operator

Yes, but it also means hash(b) == hash(x), so equality of the items isn't enough to make them the same.

Efficient way to remove keys with empty strings from a dict

For python 3

dict((k, v) for k, v in metadata.items() if v)

How to use hex() without 0x in Python?

Use this code:


it allows you to specify a number of digits too:

# '00007b'

For Python 2.6 use




Split pandas dataframe in two if it has more than 10 rows

If you have a large data frame and need to divide into a variable number of sub data frames rows, like for example each sub dataframe has a max of 4500 rows, this script could help:

max_rows = 4500
dataframes = []
while len(df) > max_rows:
    top = df[:max_rows]
    df = df[max_rows:]

You could then save out these data frames:

for _, frame in enumerate(dataframes):
    frame.to_csv(str(_)+'.csv', index=False)

Hope this helps someone!

pg_config executable not found

apt-get build-dep python-psycopg2

Checking if a website is up via Python

from urllib.request import Request, urlopen
from urllib.error import URLError, HTTPError
req = Request("")
    response = urlopen(req)
except HTTPError as e:
    print('The server couldn\'t fulfill the request.')
    print('Error code: ', e.code)
except URLError as e:
    print('We failed to reach a server.')
    print('Reason: ', e.reason)
    print ('Website is working fine')

Works on Python 3

Find the index of a dict within a list, by matching the dict's value

It won't be efficient, as you need to walk the list checking every item in it (O(n)). If you want efficiency, you can use dict of dicts. On the question, here's one possible way to find it (though, if you want to stick to this data structure, it's actually more efficient to use a generator as Brent Newey has written in the comments; see also tokland's answer):

>>> L = [{'id':'1234','name':'Jason'},
...         {'id':'2345','name':'Tom'},
...         {'id':'3456','name':'Art'}]
>>> [i for i,_ in enumerate(L) if _['name'] == 'Tom'][0]

When to use %r instead of %s in Python?

Use the %r for debugging, since it displays the "raw" data of the variable, but the others are used for displaying to users.

That's how %r formatting works; it prints it the way you wrote it (or close to it). It's the "raw" format for debugging. Here \n used to display to users doesn't work. %r shows the representation if the raw data of the variable.

months = "\nJan\nFeb\nMar\nApr\nMay\nJun\nJul\nAug"
print "Here are the months: %r" % months


Here are the months: '\nJan\nFeb\nMar\nApr\nMay\nJun\nJul\nAug'

Check this example from Learn Python the Hard Way.

Why am I getting "IndentationError: expected an indented block"?

in python intended block mean there is every thing must be written in manner in my case I written it this way

 def btnClick(numbers):
 global operator
 operator = operator + str(numbers)

Note.its give me error,until I written it in this way such that "giving spaces " then its giving me a block as I am trying to show you in function below code

def btnClick(numbers):
|global operator
|operator = operator + str(numbers)

Setting values on a copy of a slice from a DataFrame

This warning comes because your dataframe x is a copy of a slice. This is not easy to know why, but it has something to do with how you have come to the current state of it.

You can either create a proper dataframe out of x by doing

x = x.copy()

This will remove the warning, but it is not the proper way

You should be using the DataFrame.loc method, as the warning suggests, like this:

x.loc[:,'Mass32s'] = pandas.rolling_mean(x.Mass32, 5).shift(-2)

FailedPreconditionError: Attempting to use uninitialized in Tensorflow

You have to initialize variables before using them.?

If you try to evaluate the variables before initializing them you'll run into: FailedPreconditionError: Attempting to use uninitialized value tensor.

The easiest way is initializing all variables at once using: tf.global_variables_initializer()

init = tf.global_variables_initializer()
with tf.Session() as sess:

You use to run the initializer, without fetching any value.

To initialize only a subset of variables, you use tf.variables_initializer() listing the variables:

var_ab = tf.variables_initializer([a, b], name="a_and_b")
with tf.Session() as sess:

You can also initialize each variable separately using tf.Variable.initializer

# create variable W as 784 x 10 tensor, filled with zeros
W = tf.Variable(tf.zeros([784,10])) with tf.Session() as sess:

Numpy matrix to array

A, = np.array(M.T)

depends what you mean by elegance i suppose but thats what i would do

How to create a temporary directory and get the path / file name in Python

To expand on another answer, here is a fairly complete example which can cleanup the tmpdir even on exceptions:

import contextlib
import os
import shutil
import tempfile

def cd(newdir, cleanup=lambda: True):
    prevdir = os.getcwd()

def tempdir():
    dirpath = tempfile.mkdtemp()
    def cleanup():
    with cd(dirpath, cleanup):
        yield dirpath

def main():
    with tempdir() as dirpath:
        pass # do something here

How to tell if tensorflow is using gpu acceleration from inside python shell?

For Tensorflow 2.0

import tensorflow as tf


source here

other option is:


How can I search sub-folders using glob.glob module?

If you're running Python 3.4+, you can use the pathlib module. The Path.glob() method supports the ** pattern, which means “this directory and all subdirectories, recursively”. It returns a generator yielding Path objects for all matching files.

from pathlib import Path
configfiles = Path("C:/Users/sam/Desktop/file1/").glob("**/*.txt")

Access nested dictionary items via a list of keys?

This library may be helpful:

A python library for accessing and searching dictionaries via /slashed/paths ala xpath

Basically it lets you glob over a dictionary as if it were a filesystem.

pandas dataframe columns scaling with sklearn

You can do it using pandas only:

In [235]:
dfTest = pd.DataFrame({'A':[14.00,90.20,90.95,96.27,91.21],'B':[103.02,107.26,110.35,114.23,114.68], 'C':['big','small','big','small','small']})
df = dfTest[['A', 'B']]
df_norm = (df - df.min()) / (df.max() - df.min())
print df_norm
print pd.concat((df_norm, dfTest.C),1)

          A         B
0  0.000000  0.000000
1  0.926219  0.363636
2  0.935335  0.628645
3  1.000000  0.961407
4  0.938495  1.000000
          A         B      C
0  0.000000  0.000000    big
1  0.926219  0.363636  small
2  0.935335  0.628645    big
3  1.000000  0.961407  small
4  0.938495  1.000000  small

APT command line interface-like yes/no input?

For Python 3, I'm using this function:

def user_prompt(question: str) -> bool:
    """ Prompt the yes/no-*question* to the user. """
    from distutils.util import strtobool

    while True:
        user_input = input(question + " [y/n]: ")
            return bool(strtobool(user_input))
        except ValueError:
            print("Please use y/n or yes/no.\n")

The strtobool() function converts a string into a bool. If the string cant be parsed it will raise a ValueError.

In Python 3 raw_input() has been renamed to input().

As Geoff said, strtobool actually returns 0 or 1, therefore the result has to be cast to bool.

This is the implementation of strtobool, if you want special words to be recognized as true, you can copy the code and add your own cases.

def strtobool (val):
    """Convert a string representation of truth to true (1) or false (0).
    True values are 'y', 'yes', 't', 'true', 'on', and '1'; false values
    are 'n', 'no', 'f', 'false', 'off', and '0'.  Raises ValueError if
    'val' is anything else.
    val = val.lower()
    if val in ('y', 'yes', 't', 'true', 'on', '1'):
        return 1
    elif val in ('n', 'no', 'f', 'false', 'off', '0'):
        return 0
        raise ValueError("invalid truth value %r" % (val,))

Return first N key:value pairs from dict

This might not be very elegant, but works for me:

d = {'a': 3, 'b': 2, 'c': 3, 'd': 4, 'e': 5}

x= 0
for key, val in d.items():
    if x == 2:
        x += 1
        # Do something with the first two key-value pairs

Tensorflow set CUDA_VISIBLE_DEVICES within jupyter

You can set environment variables in the notebook using os.environ. Do the following before initializing TensorFlow to limit TensorFlow to first GPU.

import os
os.environ["CUDA_DEVICE_ORDER"]="PCI_BUS_ID"   # see issue #152

You can double check that you have the correct devices visible to TF

from tensorflow.python.client import device_lib
print device_lib.list_local_devices()

I tend to use it from utility module like notebook_util

import notebook_util
import tensorflow as tf

Iterating through a JSON object

for iterating through JSON you can use this:

json_object = json.loads(json_file)
for element in json_object: 
    for value in json_object['Name_OF_YOUR_KEY/ELEMENT']:

How to call an element in a numpy array?

Also, you could try to use ndarray.item(), for example, arr.item((0, 0))(rowid+colid to index) or arr.item(0)(flatten index), its doc

How can I set the aspect ratio in matplotlib?

This answer is based on Yann's answer. It will set the aspect ratio for linear or log-log plots. I've used additional information from to test if the axes are log-scale.

def forceAspect(ax,aspect=1):
    #aspect is width/height
    scale_str = ax.get_yaxis().get_scale()
    xmin,xmax = ax.get_xlim()
    ymin,ymax = ax.get_ylim()
    if scale_str=='linear':
        asp = abs((xmax-xmin)/(ymax-ymin))/aspect
    elif scale_str=='log':
        asp = abs((scipy.log(xmax)-scipy.log(xmin))/(scipy.log(ymax)-scipy.log(ymin)))/aspect

Obviously you can use any version of log you want, I've used scipy, but numpy or math should be fine.

how to stop a for loop

Try to simply use break statement.

Also you can use the following code as an example:

a = [[0,1,0], [1,0,0], [1,1,1]]
b = [[0,0,0], [0,0,0], [0,0,0]]

def check_matr(matr, expVal):    
    for row in matr:
        if len(set(row)) > 1 or set(row).pop() != expVal:
            print 'Wrong'
            break# or return
            print 'ok'
        print 'empty'
check_matr(a, 0)
check_matr(b, 0)

How can I check if an ip is in a network in Python?

I don't know of anything in the standard library, but PySubnetTree is a Python library that will do subnet matching.

Plotting a 3d cube, a sphere and a vector in Matplotlib

For drawing just the arrow, there is an easier method:-

from mpl_toolkits.mplot3d import Axes3D
import matplotlib.pyplot as plt
fig = plt.figure()
ax = fig.gca(projection='3d')

#draw the arrow

quiver can actually be used to plot multiple vectors at one go. The usage is as follows:- [ from]

quiver(X, Y, Z, U, V, W, **kwargs)


X, Y, Z: The x, y and z coordinates of the arrow locations

U, V, W: The x, y and z components of the arrow vectors

The arguments could be array-like or scalars.

Keyword arguments:

length: [1.0 | float] The length of each quiver, default to 1.0, the unit is the same with the axes

arrow_length_ratio: [0.3 | float] The ratio of the arrow head with respect to the quiver, default to 0.3

pivot: [ ‘tail’ | ‘middle’ | ‘tip’ ] The part of the arrow that is at the grid point; the arrow rotates about this point, hence the name pivot. Default is ‘tail’

normalize: [False | True] When True, all of the arrows will be the same length. This defaults to False, where the arrows will be different lengths depending on the values of u,v,w.

How can I split a text into sentences?

You could make a new tokenizer for Russian (and some other languages) using this function:

def russianTokenizer(text):
    result = text
    result = result.replace('.', ' . ')
    result = result.replace(' .  .  . ', ' ... ')
    result = result.replace(',', ' , ')
    result = result.replace(':', ' : ')
    result = result.replace(';', ' ; ')
    result = result.replace('!', ' ! ')
    result = result.replace('?', ' ? ')
    result = result.replace('\"', ' \" ')
    result = result.replace('\'', ' \' ')
    result = result.replace('(', ' ( ')
    result = result.replace(')', ' ) ') 
    result = result.replace('  ', ' ')
    result = result.replace('  ', ' ')
    result = result.replace('  ', ' ')
    result = result.replace('  ', ' ')
    result = result.strip()
    result = result.split(' ')
    return result

and then call it in this way:

text = '?? ?????????? ?????, ????????? Google SSL;'
tokens = russianTokenizer(text)

Hello World in Python

Unfortunately the xkcd comic isn't completely up to date anymore.

Since Python 3.0 you have to write:

print("Hello world!")

And someone still has to write that antigravity library :(

Single vs double quotes in JSON

You can dump JSON with double quote by:

import json

# mixing single and double quotes
data = {'jsonKey': 'jsonValue',"title": "hello world"}

# get string with all double quotes
json_string = json.dumps(data) 

Is it possible to install another version of Python to Virtualenv?

Full guide with pyenv

If pyenv is not installed then install it with pyenv-installer:

$ curl | bash

To use any custom python version, e.g. 3.5.6 use the following:

pyenv install 3.5.6
pyenv virtualenv 3.5.6 NAME_OF_YOUR_ENV
pyenv local NAME_OF_YOUR_ENV

How to convert an array of strings to an array of floats in numpy?

You can use this as well

import numpy as np
x=np.array(['1.1', '2.2', '3.3'])

Extract Google Drive zip from Google colab notebook

in my idea, you must go to a certain path for example:

from google.colab import drive drive.mount('/content/drive/') cd drive/MyDrive/f/

then :

!apt install unzip !unzip -d unzip_folder enter image description here


from sqlalchemy import desc

Usage from @jpmc26

Get first row of dataframe in Python Pandas based on criteria

For the point that 'returns the value as soon as you find the first row/record that meets the requirements and NOT iterating other rows', the following code would work:

def pd_iter_func(df):
    for row in df.itertuples():
        # Define your criteria here
        if row.A > 4 and row.B > 3:
            return row

It is more efficient than Boolean Indexing when it comes to a large dataframe.

To make the function above more applicable, one can implements lambda functions:

def pd_iter_func(df: DataFrame, criteria: Callable[[NamedTuple], bool]) -> Optional[NamedTuple]:
    for row in df.itertuples():
        if criteria(row):
            return row

pd_iter_func(df, lambda row: row.A > 4 and row.B > 3)

As mentioned in the answer to the 'mirror' question, pandas.Series.idxmax would also be a nice choice.

def pd_idxmax_func(df, mask):
    return df.loc[mask.idxmax()]

pd_idxmax_func(df, (df.A > 4) & (df.B > 3))

How to group pandas DataFrame entries by date in a non-unique column

This should work:

data.groupby(lambda x: data['date'][x].year)

How to check if a list is empty in Python?

I like Zarembisty's answer. Although, if you want to be more explicit, you can always do:

if len(my_list) == 0:
    print "my_list is empty"

Why are Python's 'private' methods not actually private?

Why are Python's 'private' methods not actually private?

As I understand it, they can't be private. How could privacy be enforced?

The obvious answer is "private members can only be accessed through self", but that wouldn't work - self is not special in Python, it is nothing more than a commonly-used name for the first parameter of a function.

'int' object has no attribute '__getitem__'

you can also covert int to str first and assign index to it then again convert it to int like this:

int(str(x)[n]) //where x is an integer value

How to transform numpy.matrix or array to scipy sparse matrix

There are several sparse matrix classes in scipy.

bsr_matrix(arg1[, shape, dtype, copy, blocksize]) Block Sparse Row matrix
coo_matrix(arg1[, shape, dtype, copy]) A sparse matrix in COOrdinate format.
csc_matrix(arg1[, shape, dtype, copy]) Compressed Sparse Column matrix
csr_matrix(arg1[, shape, dtype, copy]) Compressed Sparse Row matrix
dia_matrix(arg1[, shape, dtype, copy]) Sparse matrix with DIAgonal storage
dok_matrix(arg1[, shape, dtype, copy]) Dictionary Of Keys based sparse matrix.
lil_matrix(arg1[, shape, dtype, copy]) Row-based linked list sparse matrix

Any of them can do the conversion.

import numpy as np
from scipy import sparse

(0, 0)  1
(0, 2)  1
(1, 2)  1

See .

How do I raise the same Exception with a custom message in Python?

It seems all the answers are adding info to e.args[0], thereby altering the existing error message. Is there a downside to extending the args tuple instead? I think the possible upside is, you can leave the original error message alone for cases where parsing that string is needed; and you could add multiple elements to the tuple if your custom error handling produced several messages or error codes, for cases where the traceback would be parsed programmatically (like via a system monitoring tool).

## Approach #1, if the exception may not be derived from Exception and well-behaved:

def to_int(x):
        return int(x)
    except Exception as e:
        e.args = (e.args if e.args else tuple()) + ('Custom message',)

>>> to_int('12')

>>> to_int('12 monkeys')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 3, in to_int
ValueError: ("invalid literal for int() with base 10: '12 monkeys'", 'Custom message')


## Approach #2, if the exception is always derived from Exception and well-behaved:

def to_int(x):
        return int(x)
    except Exception as e:
        e.args += ('Custom message',)

>>> to_int('12')

>>> to_int('12 monkeys')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 3, in to_int
ValueError: ("invalid literal for int() with base 10: '12 monkeys'", 'Custom message')

Can you see a downside to this approach?

Disable output buffering

This relates to Cristóvão D. Sousa's answer, but I couldn't comment yet.

A straight-forward way of using the flush keyword argument of Python 3 in order to always have unbuffered output is:

import functools
print = functools.partial(print, flush=True)

afterwards, print will always flush the output directly (except flush=False is given).

Note, (a) that this answers the question only partially as it doesn't redirect all the output. But I guess print is the most common way for creating output to stdout/stderr in python, so these 2 lines cover probably most of the use cases.

Note (b) that it only works in the module/script where you defined it. This can be good when writing a module as it doesn't mess with the sys.stdout.

Python 2 doesn't provide the flush argument, but you could emulate a Python 3-type print function as described here .

importing external ".txt" file in python

As you can't import a .txt file, I would suggest to read words this way.

list_ = open("world.txt").read().split()

Beginner question: returning a boolean value from a function in Python

Ignoring the refactoring issues, you need to understand functions and return values. You don't need a global at all. Ever. You can do this:

def rps():
    # Code to determine if player wins
    if player_wins:
        return True

    return False

Then, just assign a value to the variable outside this function like so:

player_wins = rps()

It will be assigned the return value (either True or False) of the function you just called.

After the comments, I decided to add that idiomatically, this would be better expressed thus:

 def rps(): 
     # Code to determine if player wins, assigning a boolean value (True or False)
     # to the variable player_wins.

     return player_wins

 pw = rps()

This assigns the boolean value of player_wins (inside the function) to the pw variable outside the function.

Check if item is in an array / list

You have to use .values for arrays. for example say you have dataframe which has a column name ie, test['Name'], you can do

if name in test['Name'].values :

for a normal list you dont have to use .values

Python: How to create a unique file name?

To create a unique file path if its exist, use random package to generate a new string name for file. You may refer below code for same.

import os
import random
import string

def getUniquePath(folder, filename):    
    path = os.path.join(folder, filename)
    while os.path.exists(path):
         path = path.split('.')[0] + ''.join(random.choice(string.ascii_lowercase) for i in range(10)) + '.' + path.split('.')[1]
    return path

Now you can use this path to create file accordingly.

matplotlib colorbar in each subplot

In plt.colorbar(z1_plot,cax=ax1), use ax= instead of cax=, i.e. plt.colorbar(z1_plot,ax=ax1)

Django request get parameters

You may also use:

request.POST.get('section','') # => [39]
request.POST.get('MAINS','') # => [137] 
request.GET.get('section','') # => [39]
request.GET.get('MAINS','') # => [137]

Using this ensures that you don't get an error. If the POST/GET data with any key is not defined then instead of raising an exception the fallback value (second argument of .get() will be used).

How to increment a datetime by one day?

Most Simplest solution

from datetime import timedelta, datetime
date = datetime(2003,8,1,12,4,5)
for i in range(5):
    date += timedelta(days=1)

How to get ° character in a string in python?

Put this line at the top of your source

# -*- coding: utf-8 -*-

If your editor uses a different encoding, substitute for utf-8

Then you can include utf-8 characters directly in the source

What is the __del__ method, How to call it?

I wrote up the answer for another question, though this is a more accurate question for it.

How do constructors and destructors work?

Here is a slightly opinionated answer.

Don't use __del__. This is not C++ or a language built for destructors. The __del__ method really should be gone in Python 3.x, though I'm sure someone will find a use case that makes sense. If you need to use __del__, be aware of the basic limitations per

  • __del__ is called when the garbage collector happens to be collecting the objects, not when you lose the last reference to an object and not when you execute del object.
  • __del__ is responsible for calling any __del__ in a superclass, though it is not clear if this is in method resolution order (MRO) or just calling each superclass.
  • Having a __del__ means that the garbage collector gives up on detecting and cleaning any cyclic links, such as losing the last reference to a linked list. You can get a list of the objects ignored from gc.garbage. You can sometimes use weak references to avoid the cycle altogether. This gets debated now and then: see
  • The __del__ function can cheat, saving a reference to an object, and stopping the garbage collection.
  • Exceptions explicitly raised in __del__ are ignored.
  • __del__ complements __new__ far more than __init__. This gets confusing. See for an explanation and gotchas.
  • __del__ is not a "well-loved" child in Python. You will notice that sys.exit() documentation does not specify if garbage is collected before exiting, and there are lots of odd issues. Calling the __del__ on globals causes odd ordering issues, e.g., Should __del__ called even if the __init__ fails? See for a long thread.

But, on the other hand:

And my pesonal reason for not liking the __del__ function.

  • Everytime someone brings up __del__ it devolves into thirty messages of confusion.
  • It breaks these items in the Zen of Python:
    • Simple is better than complicated.
    • Special cases aren't special enough to break the rules.
    • Errors should never pass silently.
    • In the face of ambiguity, refuse the temptation to guess.
    • There should be one – and preferably only one – obvious way to do it.
    • If the implementation is hard to explain, it's a bad idea.

So, find a reason not to use __del__.

How can I find the dimensions of a matrix in Python?

As Ayman farhat mentioned you can use the simple method len(matrix) to get the length of rows and get the length of the first row to get the no. of columns using len(matrix[0]) :

>>> a=[[1,5,6,8],[1,2,5,9],[7,5,6,2]]
>>> len(a)
>>> len(a[0])

Also you can use a library that helps you with matrices "numpy":

>>> import numpy 
>>> numpy.shape(a)

How can strings be concatenated?

Use + for string concatenation as:

section = 'C_type'
new_section = 'Sec_' + section

Set order of columns in pandas dataframe

Try indexing (so you want a generic solution not only for this, so index order can be just what you want):

l=[0,2,1] # index order
frame=frame[[frame.columns[i] for i in l]]




   one thing second thing  other thing
0          1           0.1           a
1          2           0.2           e
2          3           1.0           i
3          4           2.0           o

Convert pyQt UI to python

Quickest way to convert .ui to .py is from terminal:

pyuic4 -x input.ui -o

Make sure you have pyqt4-dev-tools installed.

Exiting from python Command Line

"exit" is a valid variable name that can be used in your Python program. You wouldn't want to exit the interpreter when you're just trying to see the value of that variable.

How to change working directory in Jupyter Notebook?

It's simple, every time you open Jupyter Notebook and you are in your current work directory, open the Terminal in the near top right corner position where create new Python file in. The terminal in Jupyter will appear in the new tab. Type command cd <your new work directory> and enter, and then type Jupyter Notebook in that terminal, a new Jupyter Notebook will appear in the new tab with your new work directory.

Flask Python Buttons

In case anyone was still looking and came across this SO post like I did.

<input type="submit" name="open" value="Open">
<input type="submit" name="close" value="Close">

def contact():
    if "open" in request.form:
    elif "close" in request.form:
    return render_template('contact.html')

Simple, concise, and it works. Don't even need to instantiate a form object.

How to add items into a numpy array

If x is just a single scalar value, you could try something like this to ensure the correct shape of the array that is being appended/concatenated to the rightmost column of a:

import numpy as np
a = np.array([[1,3,4],[1,2,3],[1,2,1]])
x = 10
b = np.hstack((a,x*np.ones((a.shape[0],1))))

returns b as:

array([[  1.,   3.,   4.,  10.],
       [  1.,   2.,   3.,  10.],
       [  1.,   2.,   1.,  10.]])

Give column name when read csv file pandas

we can do it with a single line of code.

 user1 = pd.read_csv('dataset/1.csv', names=['TIME', 'X', 'Y', 'Z'], header=None)

How can I turn a string into a list in Python?

The list() function [docs] will convert a string into a list of single-character strings.

>>> list('hello')
['h', 'e', 'l', 'l', 'o']

Even without converting them to lists, strings already behave like lists in several ways. For example, you can access individual characters (as single-character strings) using brackets:

>>> s = "hello"
>>> s[1]
>>> s[4]

You can also loop over the characters in the string as you can loop over the elements of a list:

>>> for c in 'hello':
...     print c + c,
hh ee ll ll oo

Using Java 8's Optional with Stream::flatMap

Java 9 has been added to JDK 9. This enables you to do the following, without the need of any helper method:

Optional<Other> result =

Java 8

Yes, this was a small hole in the API, in that it's somewhat inconvenient to turn an Optional<T> into a zero-or-one length Stream<T>. You could do this:

Optional<Other> result =
          .flatMap(o -> o.isPresent() ? Stream.of(o.get()) : Stream.empty())

Having the ternary operator inside the flatMap is a bit cumbersome, though, so it might be better to write a little helper function to do this:

 * Turns an Optional<T> into a Stream<T> of length zero or one depending upon
 * whether a value is present.
static <T> Stream<T> streamopt(Optional<T> opt) {
    if (opt.isPresent())
        return Stream.of(opt.get());
        return Stream.empty();

Optional<Other> result =
          .flatMap(t -> streamopt(resolve(t)))

Here, I've inlined the call to resolve() instead of having a separate map() operation, but this is a matter of taste.

Changing the highlight color when selecting text in an HTML text input

All answers here are correct when it comes to the ::selection pseudo element, and how it works. However, the question does in fact specifically ask how to use it on text inputs.

The only way to do that is to apply the rule via a parent of the input (any parent for that matter):

.parent ::-webkit-selection, [contenteditable]::-webkit-selection {_x000D_
 background: #ffb7b7;_x000D_
.parent ::-moz-selection, [contenteditable]::-moz-selection {_x000D_
 background: #ffb7b7;_x000D_
.parent ::selection, [contenteditable]::selection {_x000D_
 background: #ffb7b7;_x000D_
/* Aesthetics */_x000D_
input, [contenteditable] {_x000D_
  border:1px solid black;_x000D_
  width: 150px;_x000D_
  height: 20px;_x000D_
  line-height: 20px;_x000D_
  padding: 3px;_x000D_
<span class="parent"><input type="text" value="Input" /></span>_x000D_
<span contenteditable>Content Editable</span>

Can I underline text in an Android layout?

check out the underscored clickable button style:

    style="@style/Widget.AppCompat.Button.Borderless.Colored" />


<string name="btn_add_contact"><u>Add new contact</u></string>


enter image description here

change figure size and figure format in matplotlib

You can change the size of the plot by adding this before you create the figure.

plt.rcParams["figure.figsize"] = [16,9]

Execute cmd command from VBScript

Can also invoke oShell.Exec in order to be able to read STDIN/STDOUT/STDERR responses. Perfect for error checking which it seems you're doing with your sanity .BAT.

What's the difference between an id and a class?

Classes are like categories. Many HTML elements can belong to a class, and an HTML element can have more than one class. Classes are used to apply general styles or styles that can be applied across multiple HTML elements.

IDs are identifiers. They're unique; no one else is allowed to have that same ID. IDs are used to apply unique styles to an HTML element.

I use IDs and classes in this fashion:

<div id="header">
  <h1>I am a header!</h1>
  <p>I am subtext for a header!</p>
<div id="content">
  <div class="section">
    <p>I am a section!</p>
  <div class="section special">
    <p>I am a section!</p>
  <div class="section">
    <p>I am a section!</p>

In this example, the header and content sections can be styled via #header and #content. Each section of the content can be applied a common style through #content .section. Just for kicks, I added a "special" class for the middle section. Suppose you wanted a particular section to have a special styling. This can be achieved with the .special class, yet the section still inherits the common styles from #content .section.

When I do JavaScript or CSS development, I typically use IDs to access/manipulate a very specific HTML element, and I use classes to access/apply styles to a broad range of elements.

How can I get date and time formats based on Culture Info?

Use a CultureInfo like this, from MSDN:

// Creates a CultureInfo for German in Germany.
CultureInfo ci = new CultureInfo("de-DE");

// Displays dt, formatted using the CultureInfo

More info on MSDN. Here is a link of all different cultures.

invalid use of non-static member function

You must make Foo::comparator static or wrap it in a std::mem_fun class object. This is because lower_bounds() expects the comparer to be a class of object that has a call operator, like a function pointer or a functor object. Also, if you are using C++11 or later, you can also do as dwcanillas suggests and use a lambda function. C++11 also has std::bind too.


// Binding:
std::lower_bounds(first, last, value, std::bind(&Foo::comparitor, this, _1, _2));
// Lambda:
std::lower_bounds(first, last, value, [](const Bar & first, const Bar & second) { return ...; });

How to solve " error=12, Cannot allocate memory" calling Runtime#exec()?

This is the solution but you have to set:

echo 1 > /proc/sys/vm/overcommit_memory

Override and reset CSS style: auto or none don't work

I believe the reason why the first set of properties will not work is because there is no auto value for display, so that property should be ignored. In that case, inline-table will still take effect, and as width do not apply to inline elements, that set of properties will not do anything.

The second set of properties will simply hide the table, as that's what display: none is for.

Try resetting it to table instead:

table.other {
    width: auto;
    min-width: 0;
    display: table;

Edit: min-width defaults to 0, not auto

How to prune local tracking branches that do not exist on remote anymore

The Powershell Version of git branch --merged master | grep -v '^[ *]*master$' | xargs git branch -d

git branch --merged master | %{ if($_ -notmatch '\*.*master'){ git branch -d "$($_.Trim())" }}

This will remove any local branches that have been merged into master, while you are on the master branch.

git checkout master to switch.

How to run multiple DOS commands in parallel?

I suggest you to see "How do I run a bat file in the background from another bat file?"

Also, good answer (of using start command) was given in "Parallel execution of shell processes" question page here;

But my recommendation is to use PowerShell. I believe it will perfectly suit your needs.

SQL MAX of multiple columns?

Well, you can use the CASE statement:

        WHEN Date1 >= Date2 AND Date1 >= Date3 THEN Date1
        WHEN Date2 >= Date1 AND Date2 >= Date3 THEN Date2
        WHEN Date3 >= Date1 AND Date3 >= Date2 THEN Date3
        ELSE                                        Date1
    END AS MostRecentDate

[For Microsoft SQL Server 2008 and above, you may consider Sven's simpler answer below.]

How to add a second x-axis in matplotlib

From matplotlib 3.1 onwards you may use ax.secondary_xaxis

import numpy as np
import matplotlib.pyplot as plt

x = np.linspace(1,13, num=301)
y = (np.sin(x)+1.01)*3000

# Define function and its inverse
f = lambda x: 1/(1+x)
g = lambda x: 1/x-1

fig, ax = plt.subplots()
ax.semilogy(x, y, label='DM')

ax2 = ax.secondary_xaxis("top", functions=(f,g))


error code 1292 incorrect date value mysql

An update. Dates of the form '2019-08-00' will trigger the same error. Adding the lines:



to mysql.cnf fixes this too. Inserting malformed dates now generates warnings for values out of range but does insert the data.

How do I get the list of keys in a Dictionary?

The question is a little tricky to understand but I'm guessing that the problem is that you're trying to remove elements from the Dictionary while you iterate over the keys. I think in that case you have no choice but to use a second array.

ArrayList lList = new ArrayList(lDict.Keys);
foreach (object lKey in lList)
  if (<your condition here>)

If you can use generic lists and dictionaries instead of an ArrayList then I would, however the above should just work.

Determining if a number is prime

If n is 2, it's prime.

If n is 1, it's not prime.

If n is even, it's not prime.

If n is odd, bigger than 2, we must check all odd numbers 3..sqrt(n)+1, if any of this numbers can divide n, n is not prime, else, n is prime.

For better performance i recommend sieve of eratosthenes.

Here is the code sample:

bool is_prime(int n)
  if (n == 2) return true;
  if (n == 1 || n % 2 == 0) return false;

  for (int i = 3; i*i < n+1; i += 2) {
      if (n % i == 0) return false;

  return true;

Fatal error in launcher: Unable to create process using ""C:\Program Files (x86)\Python33\python.exe" "C:\Program Files (x86)\Python33\pip.exe""

You can remove previous python folder and also environment variable path from you pc then Reinstall python .it will be solve

How to pass data from 2nd activity to 1st activity when pressed back? - android

Other answers were not working when I put setResult in onBackPressed. Commenting call to super onBackPressed and calling finish manually solves the problem:

public void onBackPressed() {
    Intent i = new Intent();
    i.putExtra(EXTRA_NON_DOWNLOADED_PAGES, notDownloaded);
    setResult(RESULT_OK, i);

And in first activity:

protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    if (requestCode == QUEUE_MSG) {
        if (resultCode == RESULT_OK) {
            Serializable tmp = data.getSerializableExtra(MainActivity.EXTRA_NON_DOWNLOADED_PAGES);
            if (tmp != null)
                serializable = tmp;

Wampserver icon not going green fully, mysql services not starting up?

I was running Wamp Server for more than a year,
Now I faced a problem that I couldn't start Wamp server (The icon just stay red and the error message appear)

I managed to uninstall Wamp and reinstall it again, and so I did, but before that I copied the folder from mysql/data to my desktop then when I reinstall it I copied that files to the original location.

Then mysql just got confused... And phpmyadmin is not working so I fixed that by restoring the fresh install folder contents..
But I couldn't start mysql (the wamp servers icon still on yellow)

So after I googled a lot, I deleted every thing in the mysql/data except for:-


And my problem solved :)

Javascript - sort array based on another array

Use intersection of two arrays.


var sortArray = ['a', 'b', 'c',  'd', 'e'];

var arrayToBeSort = ['z', 's', 'b',  'e', 'a'];

_.intersection(sortArray, arrayToBeSort) 

=> ['a', 'b', 'e']

if 'z and 's' are out of range of first array, append it at the end of result

Cleanest way to write retry logic?

Use Polly

Here is a retry-generic I use with Polly

public T Retry<T>(Func<T> action, int retryCount = 0)
    PolicyResult<T> policyResult = Policy

    if (policyResult.Outcome == OutcomeType.Failure)
        throw policyResult.FinalException;

    return policyResult.Result;

Use it like this

var result = Retry(() => MyFunction()), 3);

Read input stream twice

If you are using RestTemplate to make http calls Simply add an interceptor. Response body is cached by the implementation of ClientHttpResponse. Now inputstream can be retrieved from respose as many times as we need

ClientHttpRequestInterceptor interceptor =  new ClientHttpRequestInterceptor() {

            public ClientHttpResponse intercept(HttpRequest request, byte[] body,
                    ClientHttpRequestExecution execution) throws IOException {
                ClientHttpResponse  response = execution.execute(request, body);

                  // additional work before returning response
                  return response 

    // Add the interceptor to RestTemplate Instance 


When is null or undefined used in JavaScript?

I might be missing something, but afaik, you get undefined only

Update: Ok, I missed a lot, trying to complete:

You get undefined...

... when you try to access properties of an object that don't exist:

var a = {} // undefined

... when you have declared a variable but not initialized it:

var a;
// a is undefined

... when you access a parameter for which no value was passed:

function foo (a, b) {
    // something

foo(42); // b inside foo is undefined

... when a function does not return a value:

function foo() {};
var a = foo(); // a is undefined

It might be that some built-in functions return null on some error, but if so, then it is documented. null is a concrete value in JavaScript, undefined is not.

Normally you don't need to distinguish between those. Depending on the possible values of a variable, it is sufficient to use if(variable) to test whether a value is set or not (both, null and undefined evaluate to false).

Also different browsers seem to be returning these differently.

Please give a concrete example.

How do I create a dictionary with keys from a list and values defaulting to (say) zero?

In python version >= 2.7 and in python 3:

d = {el:0 for el in a}

Android EditText view Floating Hint in Material Design

Floating hint EditText:

Add below dependency in gradle:

compile ''

In layout:



Masking password input from the console : Java

If you're dealing with a Java character array (such as password characters that you read from the console), you can convert it to a JRuby string with the following Ruby code:

# GIST: "pw_from_console.rb" under ""

jconsole = Java::java.lang.System.console()
password = jconsole.readPassword()
ruby_string = ''
password.to_a.each {|c| ruby_string << c.chr}

# .. do something with 'password' variable ..    
puts "password_chars: #{password_chars.inspect}"
puts "password_string: #{password_string}"

See also "" and ""

What do I need to do to get Internet Explorer 8 to accept a self signed certificate?

It's not enough to install the certificate itself, instead you need to install the root certificate of your certification authority. Say if you use Win Server's Certificate Services, its root certificate which was created when CS was installed on that server is the one to be installed. It must be installed to the "Trusted Root Certification Authorities" as described earlier.

How to get out of while loop in java with Scanner method "hasNext" as condition?

If you don't want to use an EOF character for this, you can use StringTokenizer :

import java.util.*;
public class Test{
   public static void main(){
      Scanner sc = new Scanner (;
      System.out.print("Enter your sentence: ");
      String s=sc.nextLine();
      StringTokenizer st=new StringTokenizer(s," ");//" " is the delimiter here.
      while (st.hasMoreTokens() ) {
        String s1 = st.nextToken();

      System.out.println("The loop has been ended");

Apply CSS to jQuery Dialog Buttons

I’m reposting my answer to a similar question because no-one seems to have given it here and it’s much cleaner and neater:

Use the alternative buttons property syntax:

    autoOpen: false,
    modal: true,
    width: 600,
    resizable: false,
    buttons: [
            text: "Cancel",
            "class": 'cancelButtonClass',
            click: function() {
                // Cancel code here
            text: "Save",
            "class": 'saveButtonClass',
            click: function() {
                // Save code here
    close: function() {
        // Close code here (incidentally, same as Cancel code)

forward declaration of a struct in C?

Try this

#include <stdio.h>

struct context;

struct funcptrs{
  void (*func0)(struct context *ctx);
  void (*func1)(void);

struct context{
    struct funcptrs fps;

void func1 (void) { printf( "1\n" ); }
void func0 (struct context *ctx) { printf( "0\n" ); }

void getContext(struct context *con){
    con->fps.func0 = func0;  
    con->fps.func1 = func1;  

int main(int argc, char *argv[]){
 struct context c;
   c.fps.func0 = func0;
   c.fps.func1 = func1;
   return 0;

How to do "If Clicked Else .."

 var flag = 0;

 $('#target').click(function() {
    flag = 1;

 if (flag == 1)
   alert("Not clicked");

How to discard local changes and pull latest from GitHub repository

To push over old repo. git push -u origin master --force

I think the --force would work for a pull as well.

how to prevent this error : Warning: mysql_fetch_assoc() expects parameter 1 to be resource, boolean given in ... on line 11

You must check if result returned by mysql_query is false.

$r = mysql_qyery("...");
if ($r) {

You can use @mysql_fetch_assoc($r) to avoid error displaying.

Using variables inside strings

Use the following methods

1: Method one

var count = 123;
var message = $"Rows count is: {count}";

2: Method two

var count = 123;
var message = "Rows count is:" + count;

3: Method three

var count = 123;
var message = string.Format("Rows count is:{0}", count);

4: Method four

var count = 123;
var message = @"Rows
                is:{0}" + count;

5: Method five

var count = 123;
var message = $@"Rows 
                 is: {count}";

CSS: transition opacity on mouse-out?

You're applying transitions only to the :hover pseudo-class, and not to the element itself.

.item {   
  -webkit-transition: opacity 1s ease-in-out;
  -moz-transition: opacity 1s ease-in-out;
  -ms-transition: opacity 1s ease-in-out;
  -o-transition: opacity 1s ease-in-out;
  transition: opacity 1s ease-in-out;

.item:hover {
  zoom: 1;
  filter: alpha(opacity=50);
  opacity: 0.5;


If you don't want the transition to affect the mouse-over event, but only mouse-out, you can turn transitions off for the :hover state :

.item:hover {
  -webkit-transition: none;
  -moz-transition: none;
  -ms-transition: none;
  -o-transition: none;
  transition: none;
  zoom: 1;
  filter: alpha(opacity=50);
  opacity: 0.5;


How to close a web page on a button click, a hyperlink or a link button click?

public class Form1 : Form
public Form1()
    InitializeComponents(); // or whatever that method is called :)
    this.button.Click += new RoutedEventHandler(buttonClick);

private void buttonClick(object sender, EventArgs e)

How to read specific lines from a file (by line number)?

If the file to read is big, and you don't want to read the whole file in memory at once:

fp = open("file")
for i, line in enumerate(fp):
    if i == 25:
        # 26th line
    elif i == 29:
        # 30th line
    elif i > 29:

Note that i == n-1 for the nth line.

In Python 2.6 or later:

with open("file") as fp:
    for i, line in enumerate(fp):
        if i == 25:
            # 26th line
        elif i == 29:
            # 30th line
        elif i > 29:

validate natural input number with ngpattern

<label>Mobile Number(*)</label>
<input id="txtMobile" ng-maxlength="10" maxlength="10" Validate-phone  required  name='strMobileNo' ng-model="formModel.strMobileNo" type="text"  placeholder="Enter Mobile Number">
<span style="color:red" ng-show="regForm.strMobileNo.$dirty && regForm.strMobileNo.$invalid"><span ng-show="regForm.strMobileNo.$error.required">Phone is required.</span>

the following code will help for phone number validation and the respected directive is

app.directive('validatePhone', function() {
var PHONE_REGEXP = /^[789]\d{9}$/;
  return {
    link: function(scope, elm) {
            var isMatchRegex = PHONE_REGEXP.test(elm.val());
            if( isMatchRegex&& elm.hasClass('warning') || elm.val() == ''){
            }else if(isMatchRegex == false && !elm.hasClass('warning')){

Can I serve multiple clients using just Flask as standalone?

Tips from 2020:

From Flask 1.0, it defaults to enable multiple threads (source), you don't need to do anything, just upgrade it with:

$ pip install -U flask

If you are using flask run instead of with older versions, you can control the threaded behavior with a command option (--with-threads/--without-threads):

$ flask run --with-threads

It's same as

What does "-ne" mean in bash?

"not equal" So in this case, $RESULT is tested to not be equal to zero.

However, the test is done numerically, not alphabetically:

n1 -ne n2     True if the integers n1 and n2 are not algebraically equal.

compared to:

s1 != s2      True if the strings s1 and s2 are not identical.

2 "style" inline css img tags?

You should use :

<img src="" style="height:100px;width:100px;" alt="25"/>

That should work!!

If you want to create class then :

.size {

and then apply it like :

<img src="" class="size" alt="25"/>

by creating a class you can use it at multiple places.

If you want to use only at one place then use inline CSS. Also Inline CSS overrides other CSS.

What is a bus error?

I was getting a bus error when the root directory was at 100%.

Java: How to convert a File object to a String object in java?

Why you just not read the File line by line and add it to a StringBuffer?

After you reach end of File you can get the String from the StringBuffer.

What is the difference between a "line feed" and a "carriage return"?

Since I can not comment because of not having enough reward points I have to answer to correct answer given by @Burhan Khalid.
In very layman language Enter key press is combination of carriage return and line feed.
Carriage return points the cursor to the beginning of the line horizontly and Line feed shifts the cursor to the next line vertically.Combination of both gives you new line(\n) effect.
Reference -

What's wrong with overridable method calls in constructors?

On invoking overridable method from constructors

Simply put, this is wrong because it unnecessarily opens up possibilities to MANY bugs. When the @Override is invoked, the state of the object may be inconsistent and/or incomplete.

A quote from Effective Java 2nd Edition, Item 17: Design and document for inheritance, or else prohibit it:

There are a few more restrictions that a class must obey to allow inheritance. Constructors must not invoke overridable methods, directly or indirectly. If you violate this rule, program failure will result. The superclass constructor runs before the subclass constructor, so the overriding method in the subclass will be invoked before the subclass constructor has run. If the overriding method depends on any initialization performed by the subclass constructor, the method will not behave as expected.

Here's an example to illustrate:

public class ConstructorCallsOverride {
    public static void main(String[] args) {

        abstract class Base {
            Base() {
            abstract void overrideMe(); 

        class Child extends Base {

            final int x;

            Child(int x) {
                this.x = x;

            void overrideMe() {
        new Child(42); // prints "0"

Here, when Base constructor calls overrideMe, Child has not finished initializing the final int x, and the method gets the wrong value. This will almost certainly lead to bugs and errors.

Related questions

See also

On object construction with many parameters

Constructors with many parameters can lead to poor readability, and better alternatives exist.

Here's a quote from Effective Java 2nd Edition, Item 2: Consider a builder pattern when faced with many constructor parameters:

Traditionally, programmers have used the telescoping constructor pattern, in which you provide a constructor with only the required parameters, another with a single optional parameters, a third with two optional parameters, and so on...

The telescoping constructor pattern is essentially something like this:

public class Telescope {
    final String name;
    final int levels;
    final boolean isAdjustable;

    public Telescope(String name) {
        this(name, 5);
    public Telescope(String name, int levels) {
        this(name, levels, false);
    public Telescope(String name, int levels, boolean isAdjustable) {       = name;
        this.levels = levels;
        this.isAdjustable = isAdjustable;

And now you can do any of the following:

new Telescope("X/1999");
new Telescope("X/1999", 13);
new Telescope("X/1999", 13, true);

You can't, however, currently set only the name and isAdjustable, and leaving levels at default. You can provide more constructor overloads, but obviously the number would explode as the number of parameters grow, and you may even have multiple boolean and int arguments, which would really make a mess out of things.

As you can see, this isn't a pleasant pattern to write, and even less pleasant to use (What does "true" mean here? What's 13?).

Bloch recommends using a builder pattern, which would allow you to write something like this instead:

Telescope telly = new Telescope.Builder("X/1999").setAdjustable(true).build();

Note that now the parameters are named, and you can set them in any order you want, and you can skip the ones that you want to keep at default values. This is certainly much better than telescoping constructors, especially when there's a huge number of parameters that belong to many of the same types.

See also

Related questions

Standard way to embed version into python package?

Many of these solutions here ignore git version tags which still means you have to track version in multiple places (bad). I approached this with the following goals:

  • Derive all python version references from a tag in the git repo
  • Automate git tag/push and upload steps with a single command that takes no inputs.

How it works:

  1. From a make release command, the last tagged version in the git repo is found and incremented. The tag is pushed back to origin.

  2. The Makefile stores the version in src/ where it will be read by and also included in the release. Do not check into source control!

  3. command reads the new version string from package.__version__.



# remove optional 'v' and trailing hash "v1.0-N-HASH" -> "v1.0-N"
git_describe_ver = $(shell git describe --tags | sed -E -e 's/^v//' -e 's/(.*)-.*/\1/')
git_tag_ver      = $(shell git describe --abbrev=0)
next_patch_ver = $(shell python --patch $(call git_tag_ver))
next_minor_ver = $(shell python --minor $(call git_tag_ver))
next_major_ver = $(shell python --major $(call git_tag_ver))

    echo '__version__ = "$(call git_describe_ver)"' > $@

.PHONY: release
release: test lint mypy
    git tag -a $(call next_patch_ver)
    $(MAKE) ${MODULE}/
    python check sdist upload # (legacy "upload" method)
    # twine upload dist/*  (preferred method)
    git push origin master --tags

The release target always increments the 3rd version digit, but you can use the next_minor_ver or next_major_ver to increment the other digits. The commands rely on the script that is checked into the root of the repo

"""An auto-increment tool for version strings."""

import sys
import unittest

import click
from click.testing import CliRunner  # type: ignore

__version__ = '0.1'


@click.option('--major', 'bump_idx', flag_value=0, help='Increment major number.')
@click.option('--minor', 'bump_idx', flag_value=1, help='Increment minor number.')
@click.option('--patch', 'bump_idx', flag_value=2, default=True, help='Increment patch number.')
def cli(version: str, bump_idx: int) -> None:
    """Bumps a MAJOR.MINOR.PATCH version string at the specified index location or 'patch' digit. An
    optional 'v' prefix is allowed and will be included in the output if found."""
    prefix = version[0] if version[0].isalpha() else ''
    digits = version.lower().lstrip('v').split('.')

    if len(digits) > MAX_DIGITS:
        click.secho('ERROR: Too many digits', fg='red', err=True)

    digits = (digits + ['0'] * MAX_DIGITS)[:MAX_DIGITS]  # Extend total digits to max.
    digits[bump_idx] = str(int(digits[bump_idx]) + 1)  # Increment the desired digit.

    # Zero rightmost digits after bump position.
    for i in range(bump_idx + 1, MAX_DIGITS):
        digits[i] = '0'
    digits = digits[:max(MIN_DIGITS, bump_idx + 1)]  # Trim rightmost digits.
    click.echo(prefix + '.'.join(digits), nl=False)

if __name__ == '__main__':
    cli()  # pylint: disable=no-value-for-parameter

This does the heavy lifting how to process and increment the version number from git.

The my_module/ file is imported into my_module/ Put any static install config here that you want distributed with your module.

from ._version import __version__
__author__ = ''
__email__ = ''

The last step is to read the version info from the my_module module.

from setuptools import setup, find_packages

pkg_vars  = {}

with open("{MODULE}/") as fp:
    exec(, pkg_vars)


Of course, for all of this to work you'll have to have at least one version tag in your repo to start.

git tag -a v0.0.1

Remove Top Line of Text File with PowerShell

Using variable notation, you can do it without a temporary file:

${C:\file.txt} = ${C:\file.txt} | select -skip 1

function Remove-Topline ( [string[]]$path, [int]$skip=1 ) {
  if ( -not (Test-Path $path -PathType Leaf) ) {
    throw "invalid filename"

  ls $path |
    % { iex "`${$($_.fullname)} = `${$($_.fullname)} | select -skip $skip" }

What is the difference between Double.parseDouble(String) and Double.valueOf(String)?

Documentation for parseDouble() says "Returns a new double initialized to the value represented by the specified String, as performed by the valueOf method of class Double.", so they should be identical.

Check that a variable is a number in UNIX shell

if [ `echo $a | tr -d [:digit:] | wc -w` -eq 0 ]
    echo numeric
    echo ng


if [ `echo $a | tr -d [:digit:] | wc -w` -eq 0 ]
    echo numeric
    echo ng


RESTful Authentication

How to handle authentication in a RESTful Client-Server architecture is a matter of debate.

Commonly, it can be achieved, in the SOA over HTTP world via:

  • HTTP basic auth over HTTPS;
  • Cookies and session management;
  • Token in HTTP headers (e.g. OAuth 2.0 + JWT);
  • Query Authentication with additional signature parameters.

You'll have to adapt, or even better mix those techniques, to match your software architecture at best.

Each authentication scheme has its own PROs and CONs, depending on the purpose of your security policy and software architecture.

HTTP basic auth over HTTPS

This first solution, based on the standard HTTPS protocol, is used by most web services.

GET /spec.html HTTP/1.1
Authorization: Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ==

It's easy to implement, available by default on all browsers, but has some known drawbacks, like the awful authentication window displayed on the Browser, which will persist (there is no LogOut-like feature here), some server-side additional CPU consumption, and the fact that the user-name and password are transmitted (over HTTPS) into the Server (it should be more secure to let the password stay only on the client side, during keyboard entry, and be stored as secure hash on the Server).

We may use Digest Authentication, but it requires also HTTPS, since it is vulnerable to MiM or Replay attacks, and is specific to HTTP.

Session via Cookies

To be honest, a session managed on the Server is not truly Stateless.

One possibility could be to maintain all data within the cookie content. And, by design, the cookie is handled on the Server side (Client, in fact, does even not try to interpret this cookie data: it just hands it back to the server on each successive request). But this cookie data is application state data, so the client should manage it, not the server, in a pure Stateless world.

GET /spec.html HTTP/1.1
Cookie: theme=light; sessionToken=abc123

The cookie technique itself is HTTP-linked, so it's not truly RESTful, which should be protocol-independent, IMHO. It is vulnerable to MiM or Replay attacks.

Granted via Token (OAuth2)

An alternative is to put a token within the HTTP headers so that the request is authenticated. This is what OAuth 2.0 does, for instance. See the RFC 6749:

 GET /resource/1 HTTP/1.1
 Authorization: Bearer mF_9.B5f-4.1JqM

In short, this is very similar to a cookie and suffers to the same issues: not stateless, relying on HTTP transmission details, and subject to a lot of security weaknesses - including MiM and Replay - so is to be used only over HTTPS. Typically, a JWT is used as a token.

Query Authentication

Query Authentication consists in signing each RESTful request via some additional parameters on the URI. See this reference article.

It was defined as such in this article:

All REST queries must be authenticated by signing the query parameters sorted in lower-case, alphabetical order using the private credential as the signing token. Signing should occur before URL encoding the query string.

This technique is perhaps the more compatible with a Stateless architecture, and can also be implemented with a light session management (using in-memory sessions instead of DB persistence).

For instance, here is a generic URI sample from the link above:

GET /object?apiKey=Qwerty2010

should be transmitted as such:

GET /object?timestamp=1261496500&apiKey=Qwerty2010&signature=abcdef0123456789

The string being signed is /object?apikey=Qwerty2010&timestamp=1261496500 and the signature is the SHA256 hash of that string using the private component of the API key.

Server-side data caching can be always available. For instance, in our framework, we cache the responses at the SQL level, not at the URI level. So adding this extra parameter doesn't break the cache mechanism.

See this article for some details about RESTful authentication in our client-server ORM/SOA/MVC framework, based on JSON and REST. Since we allow communication not only over HTTP/1.1, but also named pipes or GDI messages (locally), we tried to implement a truly RESTful authentication pattern, and not rely on HTTP specificity (like header or cookies).

Later Note: adding a signature in the URI can be seen as bad practice (since for instance it will appear in the http server logs) so it has to be mitigated, e.g. by a proper TTL to avoid replays. But if your http logs are compromised, you will certainly have bigger security problems.

In practice, the upcoming MAC Tokens Authentication for OAuth 2.0 may be a huge improvement in respect to the "Granted by Token" current scheme. But this is still a work in progress and is tied to HTTP transmission.


It's worth concluding that REST is not only HTTP-based, even if, in practice, it's also mostly implemented over HTTP. REST can use other communication layers. So a RESTful authentication is not just a synonym of HTTP authentication, whatever Google answers. It should even not use the HTTP mechanism at all but shall be abstracted from the communication layer. And if you use HTTP communication, thanks to the Let's Encrypt initiative there is no reason not to use proper HTTPS, which is required in addition to any authentication scheme.

Android Recyclerview GridLayoutManager column spacing

If you want to FIXED the size of your RecyclerView item in all devices. You can do like this

public class GridSpacingItemDecoration extends RecyclerView.ItemDecoration {

    private int mSpanCount;
    private float mItemSize;

    public GridSpacingItemDecoration(int spanCount, int itemSize) {
        this.mSpanCount = spanCount;
        mItemSize = itemSize;

    public void getItemOffsets(final Rect outRect, final View view, RecyclerView parent,
            RecyclerView.State state) {
        final int position = parent.getChildLayoutPosition(view);
        final int column = position % mSpanCount;
        final int parentWidth = parent.getWidth();
        int spacing = (int) (parentWidth - (mItemSize * mSpanCount)) / (mSpanCount + 1);
        outRect.left = spacing - column * spacing / mSpanCount;
        outRect.right = (column + 1) * spacing / mSpanCount;

        if (position < mSpanCount) {
   = spacing;
        outRect.bottom = spacing;




 <dimen name="recycler_view_item_width">60dp</dimen>


int numberOfColumns = 3;
mRecyclerView.setLayoutManager(new GridLayoutManager(this, numberOfColumns));
mRecyclerView.addItemDecoration(new GridSpacingItemDecoration(3,

enter image description here enter image description here

Time complexity of accessing a Python dict

My program seems to suffer from linear access to dictionaries, its run-time grows exponentially even though the algorithm is quadratic.

I use a dictionary to memoize values. That seems to be a bottleneck.

This is evidence of a bug in your memoization method.

Django DateField default options

date = models.DateTimeField(, blank=True)

C++ style cast from unsigned char * to const char *

char * and const unsigned char * are considered unrelated types. So you want to use reinterpret_cast.

But if you were going from const unsigned char* to a non const type you'd need to use const_cast first. reinterpret_cast cannot cast away a const or volatile qualification.

String concatenation in MySQL

MySQL is different from most DBMSs use of + or || for concatenation. It uses the CONCAT function:

SELECT CONCAT(first_name, " ", last_name) AS Name FROM test.student

As @eggyal pointed out in comments, you can enable string concatenation with the || operator in MySQL by setting the PIPES_AS_CONCAT SQL mode.

How do I convert a list of ascii values to a string in python?

l = [83, 84, 65, 67, 75]

s = "".join([chr(c) for c in l])

print s

How to Copy Contents of One Canvas to Another Canvas Locally

@robert-hurst has a cleaner approach.

However, this solution may also be used, in places when you actually want to have a copy of Data Url after copying. For example, when you are building a website that uses lots of image/canvas operations.

    // select canvas elements
    var sourceCanvas = document.getElementById("some-unique-id");
    var destCanvas = document.getElementsByClassName("some-class-selector")[0];

    //copy canvas by DataUrl
    var sourceImageData = sourceCanvas.toDataURL("image/png");
    var destCanvasContext = destCanvas.getContext('2d');

    var destinationImage = new Image;
    destinationImage.onload = function(){
    destinationImage.src = sourceImageData;

How do I add BundleConfig.cs to my project?

If you are using "MVC 5" you may not see the file, and you should follow these steps:

If you are using "ASP.NET 5" it has stopped using "bundling and minification" instead was replaced by gulp, bower, and npm. More information see

Try catch statements in C

C itself doesn't support exceptions but you can simulate them to a degree with setjmp and longjmp calls.

static jmp_buf s_jumpBuffer;

void Example() { 
  if (setjmp(s_jumpBuffer)) {
    // The longjmp was executed and returned control here
    printf("Exception happened here\n");
  } else {
    // Normal code execution starts here

void Test() {
  // Rough equivalent of `throw`
  longjmp(s_jumpBuffer, 42);

This website has a nice tutorial on how to simulate exceptions with setjmp and longjmp

Plot multiple lines in one graph

The answer by @Federico Giorgi was a very good answer. It helpt me. Therefore, I did the following, in order to produce multiple lines in the same plot from the data of a single dataset, I used a for loop. Legend can be added as well.

plot(tab[,1],type="b",col="red",lty=1,lwd=2, ylim=c( min( tab, na.rm=T ),max( tab, na.rm=T ) )  )
for( i in 1:length( tab )) { [enter image description here][1]

Cause of a process being a deadlock victim

Q1:Could the time it takes for a transaction to execute make the associated process more likely to be flagged as a deadlock victim.

No. The SELECT is the victim because it had only read data, therefore the transaction has a lower cost associated with it so is chosen as the victim:

By default, the Database Engine chooses as the deadlock victim the session running the transaction that is least expensive to roll back. Alternatively, a user can specify the priority of sessions in a deadlock situation using the SET DEADLOCK_PRIORITY statement. DEADLOCK_PRIORITY can be set to LOW, NORMAL, or HIGH, or alternatively can be set to any integer value in the range (-10 to 10).

Q2. If I execute the select with a NOLOCK hint, will this remove the problem?

No. For several reasons:

Q3. I suspect that a datetime field that is checked as part of the WHERE clause in the select statement is causing the slow lookup time. Can I create an index based on this field? Is it advisable?

Probably. The cause of the deadlock is almost very likely to be a poorly indexed database.10 minutes queries are acceptable in such narrow conditions, that I'm 100% certain in your case is not acceptable.

With 99% confidence I declare that your deadlock is cased by a large table scan conflicting with updates. Start by capturing the deadlock graph to analyze the cause. You will very likely have to optimize the schema of your database. Before you do any modification, read this topic Designing Indexes and the sub-articles.

.toLowerCase not working, replacement function?

var ans = 334 + '';
var temp = ans.toLowerCase();

"Eliminate render-blocking CSS in above-the-fold content"

A related question has been asked before: What is “above-the-fold content” in Google Pagespeed?

Firstly you have to notice that this is all about 'mobile pages'.
So when I interpreted your question and screenshot correctly, then this is not for your site!

On the contrary - doing some of the things advised by Google in their guidelines will things make worse than better for 'normal' websites.
And not everything that comes from Google is the "holy grail" just because it comes from Google. And they themselves are not a good role model if you have a look at their HTML markup.

The best advice I could give you is:

  • Set width and height on replaced elements in your CSS, so that the browser can layout the elements and doesn't have to wait for the replaced content!

Additionally why do you use different CSS files, rather than just one?
The additional request is worse than the small amount of data volume. And after the first request the CSS file is cached anyway.

The things one should always take care of are:

  • reduce the number of requests as much as possible
  • keep your overall page weight as low as possible

And don't puzzle your brain about how to get 100% of Google's PageSpeed Insights tool ...! ;-)

Addition 1: Here is the page on which Google shows us, what they recommend for Optimize CSS Delivery.

As said before, I don't think that this is neither realistic nor that it makes sense for a "normal" website! Because mainly when you have a responsive web design it is most certain that you use media queries and other layout styles. So if you are not gonna load your CSS first and in a blocking manner you'll get a FOUT (Flash Of Unstyled Text). I really do not believe that this is "better" than at least some more milliseconds to render the page!

Imho Google is starting a new "hype" (when I have a look at all the question about it here on Stackoverflow) ...!

Android: How to handle right to left swipe gestures

This question was asked many years ago. Now, there is a better solution: SmartSwipe:

code looks like this:

        .addConsumer(new StayConsumer()) //contentView stay while swiping with StayConsumer
        .enableAllDirections() //enable directions as needed
        .addListener(new SimpleSwipeListener() {
            public void onSwipeOpened(SmartSwipeWrapper wrapper, SwipeConsumer consumer, int direction) {
                //  1: left
                //  2: right
                //  4: top
                //  8: bottom

Swap DIV position with CSS only

In some cases you can just use the flex-box property order.

Very simple:

.flex-item {
    order: 2;


Include headers when using SELECT INTO OUTFILE?

I was writing my code in PHP, and I had a bit of trouble using concat and union functions, and also did not use SQL variables, any ways I got it to work, here is my code:

//first I connected to the information_scheme DB

$headercon=mysqli_connect("localhost", "USERNAME", "PASSWORD", "information_schema");

//took the healders out in a string (I could not get the concat function to work, so I wrote a loop for it)

    $headers = '';
    $sql = "SELECT column_name AS columns FROM `COLUMNS` WHERE table_schema = 'YOUR_DB_NAME' AND table_name = 'YOUR_TABLE_NAME'";
    $result = $headercon->query($sql);
    while($row = $result->fetch_row())
        $headers = $headers . "'" . $row[0] . "', ";
$headers = substr("$headers", 0, -2);

// connect to the DB of interest

$con=mysqli_connect("localhost", "USERNAME", "PASSWORD", "YOUR_DB_NAME");

// export the results to csv
$result4 = $con->query($sql4);

Call ASP.NET function from JavaScript?

You can do it asynchronously using .NET Ajax PageMethods. See here or here.

Merging two CSV files using Python

When I'm working with csv files, I often use the pandas library. It makes things like this very easy. For example:

import pandas as pd

a = pd.read_csv("filea.csv")
b = pd.read_csv("fileb.csv")
b = b.dropna(axis=1)
merged = a.merge(b, on='title')
merged.to_csv("output.csv", index=False)

Some explanation follows. First, we read in the csv files:

>>> a = pd.read_csv("filea.csv")
>>> b = pd.read_csv("fileb.csv")
>>> a
   title  stage    jan    feb
0   darn  3.001  0.421  0.532
1     ok  2.829  1.036  0.751
2  three  1.115  1.146  2.921
>>> b
   title    mar    apr    may       jun  Unnamed: 5
0   darn  0.631  1.321  0.951    1.7510         NaN
1     ok  1.001  0.247  2.456    0.3216         NaN
2  three  0.285  1.283  0.924  956.0000         NaN

and we see there's an extra column of data (note that the first line of fileb.csv -- title,mar,apr,may,jun, -- has an extra comma at the end). We can get rid of that easily enough:

>>> b = b.dropna(axis=1)
>>> b
   title    mar    apr    may       jun
0   darn  0.631  1.321  0.951    1.7510
1     ok  1.001  0.247  2.456    0.3216
2  three  0.285  1.283  0.924  956.0000

Now we can merge a and b on the title column:

>>> merged = a.merge(b, on='title')
>>> merged
   title  stage    jan    feb    mar    apr    may       jun
0   darn  3.001  0.421  0.532  0.631  1.321  0.951    1.7510
1     ok  2.829  1.036  0.751  1.001  0.247  2.456    0.3216
2  three  1.115  1.146  2.921  0.285  1.283  0.924  956.0000

and finally write this out:

>>> merged.to_csv("output.csv", index=False)



static const vs #define

Using a static const is like using any other const variables in your code. This means you can trace wherever the information comes from, as opposed to a #define that will simply be replaced in the code in the pre-compilation process.

You might want to take a look at the C++ FAQ Lite for this question:

How to create a scrollable Div Tag Vertically?

Well, your code worked for me (running Chrome 5.0.307.9 and Firefox 3.5.8 on Ubuntu 9.10), though I switched

overflow-y: scroll;


overflow-y: auto;

Demo page over at:

xhtml below:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "">

<html xmlns="" xml:lang="en" lang="en">

    <META http-equiv="Content-Type" content="text/html; charset=UTF-8">

    <title>Div in table</title>
    <link rel="stylesheet" type="text/css" href="css/stylesheet.css" />

        <style type="text/css" media="all">

        th      {border-bottom: 2px solid #ccc; }

        th,td       {padding: 0.5em 1em; 
                margin: 0;
                border-collapse: collapse;

        tr td:first-child
                {border-right: 2px solid #ccc; } 

        td > div    {width: 249px;
                height: 299px;
                overflow-y: auto;

    <script type="text/javascript" src="js/jquery.js"></script>

    <script type="text/javascript">






            <tr><th>This is column one</th><th>This is column two</th><th>This is column three</th>

            <tr><td>This is row one</td><td>data point 2.1</td><td>data point 3.1</td>
            <tr><td>This is row two</td><td>data point 2.2</td><td>data point 3.2</td>
            <tr><td>This is row three</td><td>data point 2.3</td><td>data point 3.3</td>
            <tr><td>This is row four</td><td><div><p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Vestibulum ultricies mattis dolor. Class aptent taciti sociosqu ad litora torquent per conubia nostra, per inceptos himenaeos. Vestibulum a accumsan purus. Vivamus semper tempus nisi et convallis. Aliquam pretium rutrum lacus sed auctor. Phasellus viverra elit vel neque lacinia ut dictum mauris aliquet. Etiam elementum iaculis lectus, laoreet tempor ligula aliquet non. Mauris ornare adipiscing feugiat. Vivamus condimentum luctus tortor venenatis fermentum. Maecenas eu risus nec leo vehicula mattis. In nisi nibh, fermentum vitae tincidunt non, mattis eu metus. Cum sociis natoque penatibus et magnis dis parturient montes, nascetur ridiculus mus. Nunc vel est purus. Ut accumsan, elit non lacinia porta, nibh magna pretium ligula, sed iaculis metus tortor aliquam urna. Duis commodo tincidunt aliquam. Maecenas in augue ut ligula sodales elementum quis vitae risus. Vivamus mollis blandit magna, eu fringilla velit auctor sed.</p></div></td><td>data point 3.4</td>
            <tr><td>This is row five</td><td>data point 2.5</td><td>data point 3.5</td>
            <tr><td>This is row six</td><td>data point 2.6</td><td>data point 3.6</td>
            <tr><td>This is row seven</td><td>data point 2.7</td><td>data point 3.7</td>





No module named Image

You can this query:

pip install image 

I had pillow installed, and still, I got the error that you mentioned. But after I executed the above command, the error vanished. And My program worked perfectly.

ArrayList filter

write your self a filter function

 public List<T> filter(Predicate<T> criteria, List<T> list) {

And then use

    list = new Test().filter(x -> x > 2, list);

This is the most neat version in Java, but needs JDK 1.8 to support lambda calculus

Reading integers from binary file in Python

An alternative method which does not make use of 'struct.unpack()' would be to use NumPy:

import numpy as np

f = open("file.bin", "r")
a = np.fromfile(f, dtype=np.uint32)

'dtype' represents the datatype and can be int#, uint#, float#, complex# or a user defined type. See numpy.fromfile.

Personally prefer using NumPy to work with array/matrix data as it is a lot faster than using Python lists.

getch and arrow codes

The keypad will allow the keyboard of the user's terminal to allow for function keys to be interpreted as a single value (i.e. no escape sequence).

As stated in the man page:

The keypad option enables the keypad of the user's terminal. If enabled (bf is TRUE), the user can press a function key (such as an arrow key) and wgetch returns a single value representing the function key, as in KEY_LEFT. If disabled (bf is FALSE), curses does not treat function keys specially and the program has to interpret the escape sequences itself. If the keypad in the terminal can be turned on (made to transmit) and off (made to work locally), turning on this option causes the terminal keypad to be turned on when wgetch is called. The default value for keypad is false.

How can I check if a string is null or empty in PowerShell?

I have a PowerShell script I have to run on a computer so out of date that it doesn't have [String]::IsNullOrWhiteSpace(), so I wrote my own.

function IsNullOrWhitespace($str)
    if ($str)
        return ($str -replace " ","" -replace "`t","").Length -eq 0
        return $TRUE

Reload an iframe with jQuery


Session state can only be used when enableSessionState is set to true either in a configuration

I want to let everyone know that sometimes this error just is a result of some weird memory error. Restart your pc and go back into visual studio and it will be gone!! Bizarre! Try that before you start playing around with your web config file etc like I did!!!! ;-)

Unable to create/open lock file: /data/mongod.lock errno:13 Permission denied

Fix: sudo mongod

I had the same problem, running mongod with sudo privileges fixed it. Coming from a windows environment, I used just mongod to start the daemon, well it looks like we need the superuser privileges to access /data/db.

You can also give non root users Read and Write permissions to that path. check answers above for a guide!

What is dtype('O'), in pandas?

'O' stands for object.

#Loading a csv file as a dataframe
import pandas as pd 
train_df = pd.read_csv('train.csv')
col_name = 'Name of Employee'

#Checking the datatype of column name

#Instead try printing the same thing
print train_df[col_name].dtype

The first line returns: dtype('O')

The line with the print statement returns the following: object

How to resolve "The requested URL was rejected. Please consult with your administrator." error?

I have faced the same issue using Google Chrome browser. Same website was opening normally using the incognito mode and different browsers. At first, I cleared cached files and cookies over the past 24 hours, but this didn't help.

I realized that my first visit to the website was during the past 10 days. So, I cleared cached files and cookies over the past 4 weeks and that resolved the problem.
Note: I didn't clear my browsing history data

How to check if a radiobutton is checked in a radiogroup in Android?

mRadioGroup.setOnCheckedChangeListener(new RadioGroup.OnCheckedChangeListener() {
        public void onCheckedChanged(RadioGroup radioGroup, int i) {
            if (mRadioButtonMale.isChecked()) {
                text = "male";
            } else {
                text = "female";


 mRadioGroup.setOnCheckedChangeListener(new RadioGroup.OnCheckedChangeListener() {
        public void onCheckedChanged(RadioGroup radioGroup, int i) {
            if (mRadioButtonMale.isChecked()) { text = "male"; }
            if(mRadioButtonFemale.isChecked()) { text = "female"; }

How to add a form load event (currently not working)

You got half of the answer! Now that you created the event handler, you need to hook it to the form so that it actually gets called when the form is loading. You can achieve that by doing the following:

 public class ProgramViwer : Form{
  public ProgramViwer()
       Load += new EventHandler(ProgramViwer_Load);
  private void ProgramViwer_Load(object sender, System.EventArgs e)

How to send file contents as body entity using cURL

In my case, @ caused some sort of encoding problem, I still prefer my old way:

curl -d "$(cat /path/to/file)"

How can I do a case insensitive string comparison?

I think you will find more information in this link:

Use the Compare static method on the String class to compare the two strings. Whether the comparison is case-insensitive is determined by the third parameter of one of its overloads. For example:

string lowerCase = "abc";
string upperCase = "AbC";
int caseInsensitiveResult = string.Compare(lowerCase, upperCase,
int caseSensitiveResult = string.Compare(lowerCase,

The caseSensitiveResult value is -1 (indicating that lowerCase is "less than" upperCase) and the caseInsensitiveResult is zero (indicating that lowerCase "equals" upperCase).

What are Aggregates and PODs and how/why are they special?

What changes for C++11?


The standard definition of an aggregate has changed slightly, but it's still pretty much the same:

An aggregate is an array or a class (Clause 9) with no user-provided constructors (12.1), no brace-or-equal-initializers for non-static data members (9.2), no private or protected non-static data members (Clause 11), no base classes (Clause 10), and no virtual functions (10.3).

Ok, what changed?

  1. Previously, an aggregate could have no user-declared constructors, but now it can't have user-provided constructors. Is there a difference? Yes, there is, because now you can declare constructors and default them:

    struct Aggregate {
        Aggregate() = default; // asks the compiler to generate the default implementation

    This is still an aggregate because a constructor (or any special member function) that is defaulted on the first declaration is not user-provided.

  2. Now an aggregate cannot have any brace-or-equal-initializers for non-static data members. What does this mean? Well, this is just because with this new standard, we can initialize members directly in the class like this:

    struct NotAggregate {
        int x = 5; // valid in C++11
        std::vector<int> s{1,2,3}; // also valid

    Using this feature makes the class no longer an aggregate because it's basically equivalent to providing your own default constructor.

So, what is an aggregate didn't change much at all. It's still the same basic idea, adapted to the new features.

What about PODs?

PODs went through a lot of changes. Lots of previous rules about PODs were relaxed in this new standard, and the way the definition is provided in the standard was radically changed.

The idea of a POD is to capture basically two distinct properties:

  1. It supports static initialization, and
  2. Compiling a POD in C++ gives you the same memory layout as a struct compiled in C.

Because of this, the definition has been split into two distinct concepts: trivial classes and standard-layout classes, because these are more useful than POD. The standard now rarely uses the term POD, preferring the more specific trivial and standard-layout concepts.

The new definition basically says that a POD is a class that is both trivial and has standard-layout, and this property must hold recursively for all non-static data members:

A POD struct is a non-union class that is both a trivial class and a standard-layout class, and has no non-static data members of type non-POD struct, non-POD union (or array of such types). Similarly, a POD union is a union that is both a trivial class and a standard layout class, and has no non-static data members of type non-POD struct, non-POD union (or array of such types). A POD class is a class that is either a POD struct or a POD union.

Let's go over each of these two properties in detail separately.

Trivial classes

Trivial is the first property mentioned above: trivial classes support static initialization. If a class is trivially copyable (a superset of trivial classes), it is ok to copy its representation over the place with things like memcpy and expect the result to be the same.

The standard defines a trivial class as follows:

A trivially copyable class is a class that:

— has no non-trivial copy constructors (12.8),

— has no non-trivial move constructors (12.8),

— has no non-trivial copy assignment operators (13.5.3, 12.8),

— has no non-trivial move assignment operators (13.5.3, 12.8), and

— has a trivial destructor (12.4).

A trivial class is a class that has a trivial default constructor (12.1) and is trivially copyable.

[ Note: In particular, a trivially copyable or trivial class does not have virtual functions or virtual base classes.—end note ]

So, what are all those trivial and non-trivial things?

A copy/move constructor for class X is trivial if it is not user-provided and if

— class X has no virtual functions (10.3) and no virtual base classes (10.1), and

— the constructor selected to copy/move each direct base class subobject is trivial, and

— for each non-static data member of X that is of class type (or array thereof), the constructor selected to copy/move that member is trivial;

otherwise the copy/move constructor is non-trivial.

Basically this means that a copy or move constructor is trivial if it is not user-provided, the class has nothing virtual in it, and this property holds recursively for all the members of the class and for the base class.

The definition of a trivial copy/move assignment operator is very similar, simply replacing the word "constructor" with "assignment operator".

A trivial destructor also has a similar definition, with the added constraint that it can't be virtual.

And yet another similar rule exists for trivial default constructors, with the addition that a default constructor is not-trivial if the class has non-static data members with brace-or-equal-initializers, which we've seen above.

Here are some examples to clear everything up:

// empty classes are trivial
struct Trivial1 {};

// all special members are implicit
struct Trivial2 {
    int x;

struct Trivial3 : Trivial2 { // base class is trivial
    Trivial3() = default; // not a user-provided ctor
    int y;

struct Trivial4 {
    int a;
private: // no restrictions on access modifiers
    int b;

struct Trivial5 {
    Trivial1 a;
    Trivial2 b;
    Trivial3 c;
    Trivial4 d;

struct Trivial6 {
    Trivial2 a[23];

struct Trivial7 {
    Trivial6 c;
    void f(); // it's okay to have non-virtual functions

struct Trivial8 {
     int x;
     static NonTrivial1 y; // no restrictions on static members

struct Trivial9 {
     Trivial9() = default; // not user-provided
      // a regular constructor is okay because we still have default ctor
     Trivial9(int x) : x(x) {};
     int x;

struct NonTrivial1 : Trivial3 {
    virtual void f(); // virtual members make non-trivial ctors

struct NonTrivial2 {
    NonTrivial2() : z(42) {} // user-provided ctor
    int z;

struct NonTrivial3 {
    NonTrivial3(); // user-provided ctor
    int w;
NonTrivial3::NonTrivial3() = default; // defaulted but not on first declaration
                                      // still counts as user-provided
struct NonTrivial5 {
    virtual ~NonTrivial5(); // virtual destructors are not trivial


Standard-layout is the second property. The standard mentions that these are useful for communicating with other languages, and that's because a standard-layout class has the same memory layout of the equivalent C struct or union.

This is another property that must hold recursively for members and all base classes. And as usual, no virtual functions or virtual base classes are allowed. That would make the layout incompatible with C.

A relaxed rule here is that standard-layout classes must have all non-static data members with the same access control. Previously these had to be all public, but now you can make them private or protected, as long as they are all private or all protected.

When using inheritance, only one class in the whole inheritance tree can have non-static data members, and the first non-static data member cannot be of a base class type (this could break aliasing rules), otherwise, it's not a standard-layout class.

This is how the definition goes in the standard text:

A standard-layout class is a class that:

— has no non-static data members of type non-standard-layout class (or array of such types) or reference,

— has no virtual functions (10.3) and no virtual base classes (10.1),

— has the same access control (Clause 11) for all non-static data members,

— has no non-standard-layout base classes,

— either has no non-static data members in the most derived class and at most one base class with non-static data members, or has no base classes with non-static data members, and

— has no base classes of the same type as the first non-static data member.

A standard-layout struct is a standard-layout class defined with the class-key struct or the class-key class.

A standard-layout union is a standard-layout class defined with the class-key union.

[ Note: Standard-layout classes are useful for communicating with code written in other programming languages. Their layout is specified in 9.2.—end note ]

And let's see a few examples.

// empty classes have standard-layout
struct StandardLayout1 {};

struct StandardLayout2 {
    int x;

struct StandardLayout3 {
private: // both are private, so it's ok
    int x;
    int y;

struct StandardLayout4 : StandardLayout1 {
    int x;
    int y;

    void f(); // perfectly fine to have non-virtual functions

struct StandardLayout5 : StandardLayout1 {
    int x;
    StandardLayout1 y; // can have members of base type if they're not the first

struct StandardLayout6 : StandardLayout1, StandardLayout5 {
    // can use multiple inheritance as long only
    // one class in the hierarchy has non-static data members

struct StandardLayout7 {
    int x;
    int y;
    StandardLayout7(int x, int y) : x(x), y(y) {} // user-provided ctors are ok

struct StandardLayout8 {
    StandardLayout8(int x) : x(x) {} // user-provided ctors are ok
// ok to have non-static data members and other members with different access
    int x;

struct StandardLayout9 {
    int x;
    static NonStandardLayout1 y; // no restrictions on static members

struct NonStandardLayout1 {
    virtual f(); // cannot have virtual functions

struct NonStandardLayout2 {
    NonStandardLayout1 X; // has non-standard-layout member

struct NonStandardLayout3 : StandardLayout1 {
    StandardLayout1 x; // first member cannot be of the same type as base

struct NonStandardLayout4 : StandardLayout3 {
    int z; // more than one class has non-static data members

struct NonStandardLayout5 : NonStandardLayout3 {}; // has a non-standard-layout base class


With these new rules a lot more types can be PODs now. And even if a type is not POD, we can take advantage of some of the POD properties separately (if it is only one of trivial or standard-layout).

The standard library has traits to test these properties in the header <type_traits>:

template <typename T>
struct std::is_pod;
template <typename T>
struct std::is_trivial;
template <typename T>
struct std::is_trivially_copyable;
template <typename T>
struct std::is_standard_layout;

How organize uploaded media in WP?

As of October 2015, WP 4.3.1 I have found only two plugins actually affecting image locations as in “folders & subfolders”:

  • Custom Upload Dir, but as the name says, just on upload. You can work from your %post_slug% or %categories%, upload your images in the context of these post/pages, and this tool will form subfolders from it. Which is great, SEO-wise.

    Or you just even ignore all that and mandate under “Build a path template” i.e. travels/france/paris-at-night to upload to that subdir of your WP-Uploads folder. (Of course you'd have to keep changing for the uploads to follow. Limiting my overall faith, that this is a stable long-term tool, despite 10.000+ active installs).

  • Media File Manager allows to move already uploaded images and changes the paths in posts and pages using them accordingly. Its interface reminds of “Norton Commander 1.0” but it does the job. (Except for folder renames and deletes. So if you want to rename, better move images to a newly namend folder, then manually deleting the old.)

All of the following do NOT do the job:

  • WP Media Folder is NOT changing actual direcory location, thus not actually changing paths to your images thus also not affecting image URLs. Despite its name, Folder is just their visualisation of yet-another-taxonomy. I invested $19 to learn that.

  • Enhance Media Library is big, free and very popular (wordpress counts 40.000 installs) but is also not changing physical location and (thus) URLs. ? Thus the accepted answer is in my opinion wrong.

  • Media File Manager advanced appears gone and is deemed dangerous!

SQL Server - find nth occurrence in a string

You can use the following function to split the values by a delimiter. It'll return a table and to find the nth occurrence just make a select on it! Or change it a little for it to return what you need instead of the table.

    @RowData nvarchar(2000),
    @SplitOn nvarchar(5)
RETURNS @RtnValue table 
    Id int identity(1,1),
    Data nvarchar(100)
    Declare @Cnt int
    Set @Cnt = 1

    While (Charindex(@SplitOn,@RowData)>0)
        Insert Into @RtnValue (data)
            Data = ltrim(rtrim(Substring(@RowData,1,Charindex(@SplitOn,@RowData)-1)))

        Set @RowData = Substring(@RowData,Charindex(@SplitOn,@RowData)+1,len(@RowData))
        Set @Cnt = @Cnt + 1

    Insert Into @RtnValue (data)
    Select Data = ltrim(rtrim(@RowData))


Intersect Two Lists in C#

public static List<T> ListCompare<T>(List<T> List1 , List<T> List2 , string key )
    return List1.Select(t => t.GetType().GetProperty(key).GetValue(t))
                .Intersect(List2.Select(t => t.GetType().GetProperty(key).GetValue(t))).ToList();

String to char array Java

A string to char array is as simple as

String str = "someString"; 
char[] charArray = str.toCharArray();

Can you explain a little more on what you are trying to do?

* Update *

if I am understanding your new comment, you can use a byte array and example is provided.

byte[] bytes = ByteBuffer.allocate(4).putInt(1695609641).array();

for (byte b : bytes) {
   System.out.format("0x%x ", b);

With the following output

0x65 0x10 0xf3 0x29

How to change to an older version of Node.js

I had node version 6.4.0 .

As i am need of the older version 6.3.0 , i just installed the 6.3.0 version again in my system. node version downgraded automatically.

So, to downgrade the node version , Just install the older version of node js . It will get downgraded automatically from the higher version.

I tried in osx . It works like a charm .

Traverse a list in reverse order in Python

An expressive way to achieve reverse(enumerate(collection)) in python 3:

zip(reversed(range(len(collection))), reversed(collection))

in python 2:

izip(reversed(xrange(len(collection))), reversed(collection))

I'm not sure why we don't have a shorthand for this, eg.:

def reversed_enumerate(collection):
    return zip(reversed(range(len(collection))), reversed(collection))

or why we don't have reversed_range()

Java generics - get class?

I'm not 100% sure if this works in all cases (needs at least Java 1.5):

import java.lang.reflect.Field;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.util.HashMap;
import java.util.Map;

public class Main 
    public class A

    public class B extends A

    public Map<A, B> map = new HashMap<Main.A, Main.B>();

    public static void main(String[] args) 

            Field field = Main.class.getField("map");           
            System.out.println("Field " + field.getName() + " is of type " + field.getType().getSimpleName());

            Type genericType = field.getGenericType();

            if(genericType instanceof ParameterizedType)
                ParameterizedType type = (ParameterizedType) genericType;               
                Type[] typeArguments = type.getActualTypeArguments();

                for(Type typeArgument : typeArguments) 
                    Class<?> classType = ((Class<?>)typeArgument);                  
                    System.out.println("Field " + field.getName() + " has a parameterized type of " + classType.getSimpleName());
        catch(Exception e)

This will output:

Field map is of type Map
Field map has a parameterized type of A
Field map has a parameterized type of B

Use curly braces to initialize a Set in Python

There are two obvious issues with the set literal syntax:

my_set = {'foo', 'bar', 'baz'}
  1. It's not available before Python 2.7

  2. There's no way to express an empty set using that syntax (using {} creates an empty dict)

Those may or may not be important to you.

The section of the docs outlining this syntax is here.

How to add Headers on RESTful call using Jersey Client API

ClientResponse response = webResource
                               .queryParams(queryParams) //
                               .header("Content-Type", "application/json") //
                               .header("id", "123") //
                               .get(ClientResponse.class) //

MVC razor form with multiple different submit buttons?

You could also try this:

<input type="submit" name="submitbutton1" value="submit1" />
<input type="submit" name="submitbutton2" value="submit2" />

Then in your default function you call the functions you want:

if( Request.Form["submitbutton1"] != null)
    // Code for function 1
else if(Request.Form["submitButton2"] != null )
    // code for function 2

SSL: error:0B080074:x509 certificate routines:X509_check_private_key:key values mismatch

I had the same problem and finally resolved it by changing the order of pem blocks in certificate file.

The cert block should be put in the beginning of the file, then intermediate blocks, then root block.

I realized this problem by comparing a problematic certificate file with a working certificate file.

Authentication issues with WWW-Authenticate: Negotiate

Putting this information here for future readers' benefit.

  • 401 (Unauthorized) response header -> Request authentication header

  • Here are several WWW-Authenticate response headers. (The full list is at IANA: HTTP Authentication Schemes.)

    • WWW-Authenticate: Basic-> Authorization: Basic + token - Use for basic authentication
    • WWW-Authenticate: NTLM-> Authorization: NTLM + token (2 challenges)
    • WWW-Authenticate: Negotiate -> Authorization: Negotiate + token - used for Kerberos authentication
      • By the way: IANA has this angry remark about Negotiate: This authentication scheme violates both HTTP semantics (being connection-oriented) and syntax (use of syntax incompatible with the WWW-Authenticate and Authorization header field syntax).

You can set the Authorization: Basic header only when you also have the WWW-Authenticate: Basic header on your 401 challenge.

But since you have WWW-Authenticate: Negotiate this should be the case for Kerberos based authentication.

Use of alloc init instead of new

Very old question, but I've written some example just for fun — maybe you'll find it useful ;)

#import "InitAllocNewTest.h"

@implementation InitAllocNewTest

    return [super alloc];

    return [super init];


In main function both statements:

[[InitAllocNewTest alloc] init];


[InitAllocNewTest new];

result in the same output:

2013-03-06 16:45:44.125 XMLTest[18370:207] Allocating...
2013-03-06 16:45:44.128 XMLTest[18370:207] Initializing...

XML Error: Extra content at the end of the document

I've found that this error is also generated if the document is empty. In this case it's also because there is no root element - but the error message "Extra content and the end of the document" is misleading in this situation.

proper way to sudo over ssh

NOPASS in the configuration on your target machine is the solution. Continue reading at

Get domain name

Why are you using WMI? Can't you use the standard .NET functionality?


align an image and some text on the same line without using div width?

U wrote an unnecessary div, just leave it like this

<div id="texts" style="white-space:nowrap;">
     <img src="tree.png"  align="left"/>
     A very long text(about 300 words) 

What u are looking for is white-space:nowrap; this code will do the trick.

TypeScript getting error TS2304: cannot find name ' require'

For TypeScript 2.x, there are now two steps:

  1. Install a package that defines require. For example:

    npm install @types/node --save-dev
  2. Tell TypeScript to include it globally in tsconfig.json:

        "compilerOptions": {
            "types": ["node"]

The second step is only important if you need access to globally available functions such as require. For most packages, you should just use the import package from 'package' pattern. There's no need to include every package in the tsconfig.json types array above.

Convert character to Date in R

You may be overcomplicating things, is there any reason you need the stringr package?

 df <- data.frame(Date = c("10/9/2009 0:00:00", "10/15/2009 0:00:00"))
 as.Date(df$Date, "%m/%d/%Y %H:%M:%S")

[1] "2009-10-09" "2009-10-15"

More generally and if you need the time component as well, use strptime:

strptime(df$Date, "%m/%d/%Y %H:%M:%S")

I'm guessing at what your actual data might look at from the partial results you give.

How to send value attribute from radio button in PHP

Should be :


<form method="post" action="">
    <input id="name" name="name" type="text" size="40"/>
    <input type="radio" name="radio" value="test"/>Test
    <input type="submit" name="submit" value="submit"/>

PHP Code :


    echo $radio_value = $_POST["radio"];

Add & delete view from Layout

Use ViewStub and specify the layout of the view you want to toggle. To view:

mViewStub.setVisibility(View.VISIBLE) or mViewStub.inflate();

To disappear:


Node.js global variables

I agree that using the global/GLOBAL namespace for setting anything global is bad practice and don't use it at all in theory (in theory being the operative word). However (yes, the operative) I do use it for setting custom Error classes:

// Some global/configuration file that gets called in initialisation

global.MyError = [Function of MyError];

Yes, it is taboo here, but if your site/project uses custom errors throughout the place, you would basically need to define it everywhere, or at least somewhere to:

  1. Define the Error class in the first place
  2. In the script where you're throwing it
  3. In the script where you're catching it

Defining my custom errors in the global namespace saves me the hassle of require'ing my customer error library. Imaging throwing a custom error where that custom error is undefined.

Truncate a SQLite table if it exists?

**It is Simple, just follow 2 steps. Step #1. Fire query "Delete from tableName", It will delete all records from table.

Step #2. There is table named "sqlite_sequence" in Sqlite Database, just browse it and you can set sequence table wise to "0" so it will start from auto id "1".** See the screenshot attached.

enter image description here

CMake unable to determine linker language with C++

I also got the error you mention:

CMake Error: CMake can not determine linker language for target:helloworld
CMake Error: Cannot determine link language for target "helloworld".

In my case this was due to having C++ files with the .cc extension.

If CMake is unable to determine the language of the code correctly you can use the following:

set_target_properties(hello PROPERTIES LINKER_LANGUAGE CXX)

The accepted answer that suggests appending the language to the project() statement simply adds more strict checking for what language is used (according to the documentation), but it wasn't helpful to me:

Optionally you can specify which languages your project supports. Example languages are CXX (i.e. C++), C, Fortran, etc. By default C and CXX are enabled. E.g. if you do not have a C++ compiler, you can disable the check for it by explicitly listing the languages you want to support, e.g. C. By using the special language "NONE" all checks for any language can be disabled. If a variable exists called CMAKE_PROJECT__INCLUDE_FILE, the file pointed to by that variable will be included as the last step of the project command.

Angular 4 img src is not found


<img ng-src="{{imagePath}}">


<img [src]="imagePath">

How can we store into an NSDictionary? What is the difference between NSDictionary and NSMutableDictionary?

The key difference: NSMutableDictionary can be modified in place, NSDictionary cannot. This is true for all the other NSMutable* classes in Cocoa. NSMutableDictionary is a subclass of NSDictionary, so everything you can do with NSDictionary you can do with both. However, NSMutableDictionary also adds complementary methods to modify things in place, such as the method setObject:forKey:.

You can convert between the two like this:

NSMutableDictionary *mutable = [[dict mutableCopy] autorelease];
NSDictionary *dict = [[mutable copy] autorelease]; 

Presumably you want to store data by writing it to a file. NSDictionary has a method to do this (which also works with NSMutableDictionary):

BOOL success = [dict writeToFile:@"/file/path" atomically:YES];

To read a dictionary from a file, there's a corresponding method:

NSDictionary *dict = [NSDictionary dictionaryWithContentsOfFile:@"/file/path"];

If you want to read the file as an NSMutableDictionary, simply use:

NSMutableDictionary *dict = [NSMutableDictionary dictionaryWithContentsOfFile:@"/file/path"];

Differences in boolean operators: & vs && and | vs ||

& and | provide the same outcome as the && and || operators. The difference is that they always evaluate both sides of the expression where as && and || stop evaluating if the first condition is enough to determine the outcome.

What is the difference between RTP or RTSP in a streaming server?

Some basics:

RTSP server can be used for dead source as well as for live source. RTSP protocols provides you commands (Like your VCR Remote), and functionality depends upon your implementation.

RTP is real time protocol used for transporting audio and video in real time. Transport used can be unicast, multicast or broadcast, depending upon transport address and port. Besides transporting RTP does lots of things for you like packetization, reordering, jitter control, QoS, support for Lip sync.....

In your case if you want broadcasting streaming server then you need both RTSP (for control) as well as RTP (broadcasting audio and video)

To start with you can go through sample code provided by live555

Use string in switch case in java

Here is a possible pre-1.7 way, which I can't recommend:

public class PoorSwitch
    final static public int poorHash (String s) {
        long l = 0L;
        for (char c: s.toCharArray ()) {
            l = 97*l + c;
        return (int) l;

    public static void main (String args[])
        String param = "foo";
        if (args.length == 1)
            param = args[0];
        // uncomment these lines, to evaluate your hash
        // test ("foo");
        // test ("bar");
        switch (poorHash (param)) {
            // this doesn't work, since you need a literal constant
            // so we have to evaluate our hash beforehand:
            // case poorHash ("foo"): {
            case 970596: {
                System.out.println ("Foo!");
            // case poorHash ("bar"): {
            case 931605: {
                System.out.println ("Bar!");
            default: {
                System.out.println ("unknown\t" + param);

    public static void test (String s)
        System.out.println ("Hash:\t " + s + " =\t" + poorHash (s));

Maybe you could work with such a trick in a generated code. Else I can't recommend it. Not so much that the possibility of a hash collision makes me worry, but if something is mixed up (cut and paste), it is hard to find the error. 931605 is not a good documentation.

Take it just as proof of concept, as curiosity.

What is the main difference between Inheritance and Polymorphism?

Inheritance is when a 'class' derives from an existing 'class'. So if you have a Person class, then you have a Student class that extends Person, Student inherits all the things that Person has. There are some details around the access modifiers you put on the fields/methods in Person, but that's the basic idea. For example, if you have a private field on Person, Student won't see it because its private, and private fields are not visible to subclasses.

Polymorphism deals with how the program decides which methods it should use, depending on what type of thing it has. If you have a Person, which has a read method, and you have a Student which extends Person, which has its own implementation of read, which method gets called is determined for you by the runtime, depending if you have a Person or a Student. It gets a bit tricky, but if you do something like

Person p = new Student();;

the read method on Student gets called. Thats the polymorphism in action. You can do that assignment because a Student is a Person, but the runtime is smart enough to know that the actual type of p is Student.

Note that details differ among languages. You can do inheritance in javascript for example, but its completely different than the way it works in Java.

How to lookup JNDI resources on WebLogic?

I had a similar problem to this one. It got solved by deleting the java:comp/env/ prefix and using jdbc/myDataSource in the context lookup. Just as someone pointed out in the comments.

PostgreSQL Autoincrement

You have to be careful not to insert directly into your SERIAL or sequence field, otherwise your write will fail when the sequence reaches the inserted value:

-- Table: "test"

-- DROP TABLE test;

  "Rank" integer NOT NULL,
  "GermanHeadword" "text" [] NOT NULL,
  "PartOfSpeech" "text" NOT NULL,
  "ExampleSentence" "text" NOT NULL,
  "EnglishGloss" "text"[] NOT NULL,
-- ALTER TABLE test OWNER TO postgres;
 INSERT INTO test("Rank", "GermanHeadword", "PartOfSpeech", "ExampleSentence", "EnglishGloss")
           VALUES (1, '{"der", "die", "das", "den", "dem", "des"}', 'art', 'Der Mann küsst die Frau und das Kind schaut zu', '{"the", "of the" }');

 INSERT INTO test("ID", "Rank", "GermanHeadword", "PartOfSpeech", "ExampleSentence", "EnglishGloss")
           VALUES (2, 1, '{"der", "die", "das"}', 'pron', 'Das ist mein Fahrrad', '{"that", "those"}');

 INSERT INTO test("Rank", "GermanHeadword", "PartOfSpeech", "ExampleSentence", "EnglishGloss")
           VALUES (1, '{"der", "die", "das"}', 'pron', 'Die Frau, die nebenen wohnt, heißt Renate', '{"that", "who"}');

SELECT * from test; 

React Hook "useState" is called in function "app" which is neither a React function component or a custom React Hook function

Do not use arrow function to create functional components.

Do as one of the examples below:

function MyComponent(props) {
  const [states, setStates] = React.useState({ value: '' });

  return (
      onChange={(event) => setStates({ value: })}


//IMPORTANT: Repeat the function name

const MyComponent = function MyComponent(props) { 
  const [states, setStates] = React.useState({ value: '' });

  return (
      onChange={(event) => setStates({ value: })}

If you have problems with "ref" (probably in loops), the solution is to use forwardRef():

// IMPORTANT: Repeat the function name
// Add the "ref" argument to the function, in case you need to use it.

const MyComponent = React.forwardRef( function MyComponent(props, ref) {
  const [states, setStates] = React.useState({ value: '' });

  return (
      onChange={(event) => setStates({ value: })}

Python Traceback (most recent call last)

In Python2, input is evaluated, input() is equivalent to eval(raw_input()). When you enter klj, Python tries to evaluate that name and raises an error because that name is not defined.

Use raw_input to get a string from the user in Python2.

Demo 1: klj is not defined:

>>> input()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<string>", line 1, in <module>
NameError: name 'klj' is not defined

Demo 2: klj is defined:

>>> klj = 'hi'
>>> input()

Demo 3: getting a string with raw_input:

>>> raw_input()

Why shouldn't I use mysql_* functions in PHP?

Speaking of technical reasons, there are only a few, extremely specific and rarely used. Most likely you will never ever use them in your life.
Maybe I am too ignorant, but I never had an opportunity to use them things like

  • non-blocking, asynchronous queries
  • stored procedures returning multiple resultsets
  • Encryption (SSL)
  • Compression

If you need them - these are no doubt technical reasons to move away from mysql extension toward something more stylish and modern-looking.

Nevertheless, there are also some non-technical issues, which can make your experience a bit harder

  • further use of these functions with modern PHP versions will raise deprecated-level notices. They simply can be turned off.
  • in a distant future, they can be possibly removed from the default PHP build. Not a big deal too, as mydsql ext will be moved into PECL and every hoster will be happy to compile PHP with it, as they don't want to lose clients whose sites were working for decades.
  • strong resistance from Stackoverflow community. ?verytime you mention these honest functions, you being told that they are under strict taboo.
  • being an average PHP user, most likely your idea of using these functions is error-prone and wrong. Just because of all these numerous tutorials and manuals which teach you the wrong way. Not the functions themselves - I have to emphasize it - but the way they are used.

This latter issue is a problem.
But, in my opinion, the proposed solution is no better either.
It seems to me too idealistic a dream that all those PHP users will learn how to handle SQL queries properly at once. Most likely they would just change mysql_* to mysqli_* mechanically, leaving the approach the same. Especially because mysqli makes prepared statements usage incredible painful and troublesome.
Not to mention that native prepared statements aren't enough to protect from SQL injections, and neither mysqli nor PDO offers a solution.

So, instead of fighting this honest extension, I'd prefer to fight wrong practices and educate people in the right ways.

Also, there are some false or non-significant reasons, like

  • Doesn't support Stored Procedures (we were using mysql_query("CALL my_proc"); for ages)
  • Doesn't support Transactions (same as above)
  • Doesn't support Multiple Statements (who need them?)
  • Not under active development (so what? does it affect you in any practical way?)
  • Lacks an OO interface (to create one is a matter of several hours)
  • Doesn't support Prepared Statements or Parametrized Queries

The last one is an interesting point. Although mysql ext do not support native prepared statements, they aren't required for the safety. We can easily fake prepared statements using manually handled placeholders (just like PDO does):

function paraQuery()
    $args  = func_get_args();
    $query = array_shift($args);
    $query = str_replace("%s","'%s'",$query); 

    foreach ($args as $key => $val)
        $args[$key] = mysql_real_escape_string($val);

    $query  = vsprintf($query, $args);
    $result = mysql_query($query);
    if (!$result)
        throw new Exception(mysql_error()." [$query]");
    return $result;

$query  = "SELECT * FROM table where a=%s AND b LIKE %s LIMIT %d";
$result = paraQuery($query, $a, "%$b%", $limit);

voila, everything is parameterized and safe.

But okay, if you don't like the red box in the manual, a problem of choice arises: mysqli or PDO?

Well, the answer would be as follows:

  • If you understand the necessity of using a database abstraction layer and looking for an API to create one, mysqli is a very good choice, as it indeed supports many mysql-specific features.
  • If, like vast majority of PHP folks, you are using raw API calls right in the application code (which is essentially wrong practice) - PDO is the only choice, as this extension pretends to be not just API but rather a semi-DAL, still incomplete but offers many important features, with two of them makes PDO critically distinguished from mysqli:

    • unlike mysqli, PDO can bind placeholders by value, which makes dynamically built queries feasible without several screens of quite messy code.
    • unlike mysqli, PDO can always return query result in a simple usual array, while mysqli can do it only on mysqlnd installations.

So, if you are an average PHP user and want to save yourself a ton of headaches when using native prepared statements, PDO - again - is the only choice.
However, PDO is not a silver bullet too and has its hardships.
So, I wrote solutions for all the common pitfalls and complex cases in the PDO tag wiki

Nevertheless, everyone talking about extensions always missing the 2 important facts about Mysqli and PDO:

  1. Prepared statement isn't a silver bullet. There are dynamical identifiers which cannot be bound using prepared statements. There are dynamical queries with an unknown number of parameters which makes query building a difficult task.

  2. Neither mysqli_* nor PDO functions should have appeared in the application code.
    There ought to be an abstraction layer between them and application code, which will do all the dirty job of binding, looping, error handling, etc. inside, making application code DRY and clean. Especially for the complex cases like dynamical query building.

So, just switching to PDO or mysqli is not enough. One has to use an ORM, or a query builder, or whatever database abstraction class instead of calling raw API functions in their code.
And contrary - if you have an abstraction layer between your application code and mysql API - it doesn't actually matter which engine is used. You can use mysql ext until it goes deprecated and then easily rewrite your abstraction class to another engine, having all the application code intact.

Here are some examples based on my safemysql class to show how such an abstraction class ought to be:

$city_ids = array(1,2,3);
$cities   = $db->getCol("SELECT name FROM cities WHERE is IN(?a)", $city_ids);

Compare this one single line with amount of code you will need with PDO.
Then compare with crazy amount of code you will need with raw Mysqli prepared statements. Note that error handling, profiling, query logging already built in and running.

$insert = array('name' => 'John', 'surname' => "O'Hara");
$db->query("INSERT INTO users SET ?u", $insert);

Compare it with usual PDO inserts, when every single field name being repeated six to ten times - in all these numerous named placeholders, bindings, and query definitions.

Another example:

$data = $db->getAll("SELECT * FROM goods ORDER BY ?n", $_GET['order']);

You can hardly find an example for PDO to handle such practical case.
And it will be too wordy and most likely unsafe.

So, once more - it is not just raw driver should be your concern but abstraction class, useful not only for silly examples from beginner's manual but to solve whatever real-life problems.

The type or namespace name 'Objects' does not exist in the namespace 'System.Data'

In my case for EF 6+, when using this:


As part of this command:

var sql = ((System.Data.Entity.Core.Objects.ObjectQuery)query).ToTraceString();

I got this error:

Cannot cast 'query' (which has an actual type of 'System.Data.Entity.Infrastructure.DbQuery<<>f__AnonymousType3<string,string,string,short,string>>') to 'System.Data.Entity.Core.Objects.ObjectQuery'

So I ended up having to use this:

var sql = ((System.Data.Entity.Infrastructure.DbQuery<<>f__AnonymousType3<string,string,string,short,string>>)query).ToString();    

Of course your anonymous type signature might be different.


How do you check if a variable is an array in JavaScript?

I personally like Peter's suggestion: (for ECMAScript 3. For ECMAScript 5, use Array.isArray())

Comments on the post indicate, however, that if toString() is changed at all, that way of checking an array will fail. If you really want to be specific and make sure toString() has not been changed, and there are no problems with the objects class attribute ([object Array] is the class attribute of an object that is an array), then I recommend doing something like this:

//see if toString returns proper class attributes of objects that are arrays
//returns -1 if it fails test
//returns true if it passes test and it's an array
//returns false if it passes test and it's not an array
function is_array(o)
    // make sure an array has a class attribute of [object Array]
    var check_class =[]);
    if(check_class === '[object Array]')
        // test passed, now check
        return === '[object Array]';
        // may want to change return value to something more desirable
        return -1; 

Note that in JavaScript The Definitive Guide 6th edition, 7.10, it says Array.isArray() is implemented using in ECMAScript 5. Also note that if you're going to worry about toString()'s implementation changing, you should also worry about every other built in method changing too. Why use push()? Someone can change it! Such an approach is silly. The above check is an offered solution to those worried about toString() changing, but I believe the check is unnecessary.

Javascript get Object property Name

I was searching to get a result for this either and I ended up with;

const MyObject = {
    SubObject: {
        'eu': [0, "asd", true, undefined],
        'us': [0, "asd", false, null],
        'aus': [0, "asd", false, 0]

For those who wanted the result as a string:


output: "eu,us,aus"

For those who wanted the result as an array:


output: Array ["eu", "us", "aus"]

For those who are looking for a "contains" type method: as numeric result:


output: -1


output: 0


output: 3

as boolean result:


output: true

In your case;

var myVar = { typeA: { option1: "one", option2: "two" } }_x000D_
    // Example 1_x000D_
    console.log(Object.keys(myVar.typeA).toString()); // Result: "option1, option2"_x000D_
    // Example 2_x000D_
    console.log(Array.from(Object.keys(myVar.typeA))); // Result: Array ["option1", "option2" ]_x000D_
    // Example 3 as numeric_x000D_
    console.log((Object.keys(myVar.typeA).indexOf("option1")>=0)?'Exist!':'Does not exist!'); // Result: Exist!_x000D_
    // Example 3 as boolean_x000D_
    console.log(Object.keys(myVar.typeA).includes("option2")); // Result: True!_x000D_
    // if you would like to know about SubObjects_x000D_
    for(var key in myVar){_x000D_
      // do smt with SubObject_x000D_
      console.log(key); // Result: typeA_x000D_
    // if you already know your "SubObject"_x000D_
    for(var key in myVar.typeA){_x000D_
      // do smt with option1, option2_x000D_
      console.log(key); // Result: option1 // Result: option2_x000D_

POST request send json data java HttpUrlConnection

Your JSON is not correct. Instead of

JSONObject cred = new JSONObject();
JSONObject auth=new JSONObject();
JSONObject parent=new JSONObject();
cred.put("password", "pwd");
auth.put("tenantName", "adm");
auth.put("passwordCredentials", cred.toString()); // <-- toString()
parent.put("auth", auth.toString());              // <-- toString()

OutputStreamWriter wr= new OutputStreamWriter(con.getOutputStream());


JSONObject cred = new JSONObject();
JSONObject auth=new JSONObject();
JSONObject parent=new JSONObject();
cred.put("password", "pwd");
auth.put("tenantName", "adm");
auth.put("passwordCredentials", cred);
parent.put("auth", auth);

OutputStreamWriter wr= new OutputStreamWriter(con.getOutputStream());

So, the JSONObject.toString() should be called only once for the outer object.

Another thing (most probably not your problem, but I'd like to mention it):

To be sure not to run into encoding problems, you should specify the encoding, if it is not UTF-8:

con.setRequestProperty("Content-Type", "application/json; charset=UTF-8");
con.setRequestProperty("Accept", "application/json");

// ...

OutputStream os = con.getOutputStream();

How to delete multiple pandas (python) dataframes from memory to save RAM?

del statement does not delete an instance, it merely deletes a name.

When you do del i, you are deleting just the name i - but the instance is still bound to some other name, so it won't be Garbage-Collected.

If you want to release memory, your dataframes has to be Garbage-Collected, i.e. delete all references to them.

If you created your dateframes dynamically to list, then removing that list will trigger Garbage Collection.

>>> lst = [pd.DataFrame(), pd.DataFrame(), pd.DataFrame()]
>>> del lst     # memory is released

If you created some variables, you have to delete them all.

>>> a, b, c = pd.DataFrame(), pd.DataFrame(), pd.DataFrame()
>>> lst = [a, b, c]
>>> del a, b, c # dfs still in list
>>> del lst     # memory release now

How to shuffle an ArrayList

Use this method and pass your array in parameter


This method return void so it will not give you a new list but as we know that array is passed as a reference type in Java so it will shuffle your array and save shuffled values in it. That's why you don't need any return type.

You can now use arraylist which is shuffled.

TypeError: 'str' object is not callable (Python)

An issue I just had was accidentally calling a string

"Foo" ("Bar" if bar else "Baz")

You can concatenate string by just putting them next to each other like so

"Foo" "Bar"

however because of the open brace in the first example it thought I was trying to call "Foo"

How can I increment a date by one day in Java?

Let's clarify the use case: You want to do calendar arithmetic and start/end with a java.util.Date.

Some approaches:

  1. Convert to string and back with SimpleDateFormat: This is an inefficient solution.
  2. Convert to LocalDate: You would lose any time-of-day information.
  3. Convert to LocalDateTime: This involves more steps and you need to worry about timezone.
  4. Convert to epoch with Date.getTime(): This is efficient but you are calculating with milliseconds.

Consider using java.time.Instant:

Date _now = new Date();
Instant _instant = _now.toInstant().minus(5, ChronoUnit.DAYS);
Date _newDate = Date.from(_instant);

Does height and width not apply to span?

As per comment from @Paul, If display: block is specified, span stops to be an inline element and an element after it appears on next line.

I came here to find solution to my span height problem and I got a solution of my own

Adding overflow:hidden; and keeing it inline will solve the problem just tested in IE8 Quirks mode

How to access a RowDataPacket object

Simpler way:

.then( resp=> {
  let resultFromDb= Object.values(resp)[0]

In my example I received an object in response. When I use Object.values I have the value of the property as a response, however it comes inside an array, using [0] access the first index of this array, now i have the value to use it where I need it.

How to use mod operator in bash?

for i in {1..600}

Get name of property as a string

it's how I implemented it , the reason behind is if the class that you want to get the name from it's member is not static then you need to create an instanse of that and then get the member's name. so generic here comes to help

public static string GetName<TClass>(Expression<Func<TClass, object>> exp)
    MemberExpression body = exp.Body as MemberExpression;

    if (body == null)
         UnaryExpression ubody = (UnaryExpression)exp.Body;
         body = ubody.Operand as MemberExpression;

     return body.Member.Name;

the usage is like this

var label = ClassExtension.GetName<SomeClass>(x => x.Label); //x is refering to 'SomeClass'

How to scroll to specific item using jQuery?

Not sure why no one says the obvious, as there's a built in javascript scrollTo function:

scrollTo( $('#element').position().top );


Regex Email validation

To validate your email ID, you can simply create such method and use it.

    public static bool IsValidEmail(string email)
        var r = new Regex(@"^([0-9a-zA-Z]([-\.\w]*[0-9a-zA-Z])*@([0-9a-zA-Z][-\w]*[0-9a-zA-Z]\.)+[a-zA-Z]{2,9})$");
        return !String.IsNullOrEmpty(email) && r.IsMatch(email);

This will return True / False. (Valid / Invalid Email Id)

How should the ViewModel close the form?

public partial class MyWindow: Window
    public ApplicationSelection()

      MyViewModel viewModel = new MyViewModel();

      DataContext = viewModel;

      viewModel.RequestClose += () => { Close(); };


public class MyViewModel

  //...Your code...

  public event Action RequestClose;

  public virtual void Close()
    if (RequestClose != null)

  public void SomeFunction()
     //...Do something...

How do I find out which computer is the domain controller in Windows programmatically?

In C#/.NET 3.5 you could write a little program to do:

using (PrincipalContext context = new PrincipalContext(ContextType.Domain))
    string controller = context.ConnectedServer;
    Console.WriteLine( "Domain Controller:" + controller );

This will list all the users in the current domain:

using (PrincipalContext context = new PrincipalContext(ContextType.Domain))
    using (UserPrincipal searchPrincipal = new UserPrincipal(context))
       using (PrincipalSearcher searcher = new PrincipalSearcher(searchPrincipal))
           foreach (UserPrincipal principal in searcher.FindAll())
               Console.WriteLine( principal.SamAccountName);

How to initialize a List<T> to a given size (as opposed to capacity)?

Use the constructor which takes an int ("capacity") as an argument:

List<string> = new List<string>(10);

EDIT: I should add that I agree with Frederik. You are using the List in a way that goes against the entire reasoning behind using it in the first place.


EDIT 2: What I'm currently writing is a base class offering default functionality as part of a bigger framework. In the default functionality I offer, the size of the List is known in advanced and therefore I could have used an array. However, I want to offer any base class the chance to dynamically extend it and therefore I opt for a list.

Why would anyone need to know the size of a List with all null values? If there are no real values in the list, I would expect the length to be 0. Anyhow, the fact that this is cludgy demonstrates that it is going against the intended use of the class.

Get month name from number

Some good answers already make use of calendar but the effect of setting the locale hasn't been mentioned yet.

Calendar set month names according to the current locale, for exemple in French:

import locale
import calendar

locale.setlocale(locale.LC_ALL, 'fr_FR')

assert calendar.month_name[1] == 'janvier'
assert calendar.month_abbr[1] == 'jan'

If you plan on using setlocale in your code, make sure to read the tips and caveats and extension writer sections from the documentation. The example shown here is not representative of how it should be used. In particular, from these two sections:

It is generally a bad idea to call setlocale() in some library routine, since as a side effect it affects the entire program […]

Extension modules should never call setlocale() […]

Unzip All Files In A Directory

This is a variant of Pedro Lobito answer using How to loop through a directory recursively to delete files with certain extensions teachings:

shopt -s globstar

for zip_file_name in **/*.{zip,sublime\-package}; do
    directory_name=`echo $zip_file_name | sed 's/\.\(zip\|sublime\-package\)$//'`
    printf "Unpacking zip file \`$root_directory/$zip_file_name\`...\n"

    if [ -f "$root_directory/$zip_file_name" ]; then
        mkdir -p "$root_directory/$directory_name"
        unzip -o -q "$root_directory/$zip_file_name" -d "$directory_name"

        # Some files have the executable flag and were not being deleted because of it.
        # chmod -x "$root_directory/$zip_file_name"
        # rm -f "$root_directory/$zip_file_name"

How to set index.html as root file in Nginx?

According to the documentation Checks the existence of files in the specified order and uses the first found file for request processing; the processing is performed in the current context. The path to a file is constructed from the file parameter according to the root and alias directives. It is possible to check directory’s existence by specifying a slash at the end of a name, e.g. “$uri/”. If none of the files were found, an internal redirect to the uri specified in the last parameter is made. Important

an internal redirect to the uri specified in the last parameter is made.

So in last parameter you should add your page or code if first two parameters returns false.

location / {
  try_files $uri $uri/index.html index.html;

jQuery scrollTop() doesn't seem to work in Safari or Chrome (Windows)

I my case, the button was working for two of 8 links. My solution was


This created a nice scroll effect as well

Mock a constructor with parameter

With mockito you can use withSettings(), for example if the CounterService required 2 dependencies, you can pass them as a mock:

UserService userService = Mockito.mock(UserService.class); SearchService searchService = Mockito.mock(SearchService.class); CounterService counterService = Mockito.mock(CounterService.class, withSettings().useConstructor(userService, searchService));

Does MS Access support "CASE WHEN" clause if connect with ODBC?

I have had to use a multiple IIF statement to create a similar result in ACCESS SQL.

IIf([refi type] Like "FHA ST*","F",IIf([refi type]="VA IRRL","V"))

All remaining will stay Null.

How to send a “multipart/form-data” POST in Android with Volley

Another solution, very light with high performance with payload large:

Android Asynchronous Http Client library:

private static AsyncHttpClient client = new AsyncHttpClient();

private void uploadFileExecute(File file) {

    RequestParams params = new RequestParams();

    try { params.put("photo", file); } catch (FileNotFoundException e) {}, params,

        new AsyncHttpResponseHandler() {

            public void onSuccess(String result) {

                Log.d(TAG,"uploadFile response: "+result);


            public void onFailure(Throwable arg0, String errorMsg) {

                Log.d(TAG,"uploadFile ERROR!");





How can I split a shell command over multiple lines when using an IF statement?

The line-continuation will fail if you have whitespace (spaces or tab characters[1]) after the backslash and before the newline. With no such whitespace, your example works fine for me:

$ cat
if ! fab --fabfile=.deploy/ \
   --forward-agent \
   --disable-known-hosts deploy:$target; then
     echo failed
     echo succeeded

$ alias fab=true; . ./
$ alias fab=false; . ./

Some detail promoted from the comments: the line-continuation backslash in the shell is not really a special case; it is simply an instance of the general rule that a backslash "quotes" the immediately-following character, preventing any special treatment it would normally be subject to. In this case, the next character is a newline, and the special treatment being prevented is terminating the command. Normally, a quoted character winds up included literally in the command; a backslashed newline is instead deleted entirely. But otherwise, the mechanism is the same. Most importantly, the backslash only quotes the immediately-following character; if that character is a space or tab, you just get a literal space or tab, and any subsequent newline remains unquoted.

[1] or carriage returns, for that matter, as Czechnology points out. Bash does not get along with Windows-formatted text files, not even in WSL. Or Cygwin, but at least their Bash port has added a set -o igncr option that you can set to make it carriage-return-tolerant.

Change collations of all columns of all tables in SQL Server

Fixed length problem nvarchar and added NULL/NOT NULL

DECLARE @collate nvarchar(100);
DECLARE @table nvarchar(255);
DECLARE @column_name nvarchar(255);
DECLARE @column_id int;
DECLARE @data_type nvarchar(255);
DECLARE @max_length int;
DECLARE @row_id int;
DECLARE @sql nvarchar(max);
DECLARE @sql_column nvarchar(max);
DECLARE @is_Nullable bit;
DECLARE @null nvarchar(25);

SET @collate = 'Latin1_General_CI_AS';

DECLARE local_table_cursor CURSOR FOR

SELECT [name]
FROM sysobjects

OPEN local_table_cursor
FETCH NEXT FROM local_table_cursor
INTO @table


    DECLARE local_change_cursor CURSOR FOR

    SELECT ROW_NUMBER() OVER (ORDER BY c.column_id) AS row_id
        , column_name
        , t.Name data_type
        , c.max_length
        , c.column_id
        , c.is_nullable
    FROM sys.columns c
    JOIN sys.types t ON c.system_type_id = t.system_type_id
    LEFT OUTER JOIN sys.index_columns ic ON ic.object_id = c.object_id AND ic.column_id = c.column_id
    LEFT OUTER JOIN sys.indexes i ON ic.object_id = i.object_id AND ic.index_id = i.index_id
    WHERE c.object_id = OBJECT_ID(@table)
    ORDER BY c.column_id

    OPEN local_change_cursor
    FETCH NEXT FROM local_change_cursor
    INTO @row_id, @column_name, @data_type, @max_length, @column_id, @is_nullable


        IF (@max_length = -1) SET @max_length = 4000;
        set @null=' NOT NULL'
        if (@is_nullable = 1) Set @null=' NULL'
        if (@Data_type='nvarchar') set @max_length=cast(@max_length/2 as bigint)
        IF (@data_type LIKE '%char%')
        BEGIN TRY
            SET @sql = 'ALTER TABLE ' + @table + ' ALTER COLUMN [' + rtrim(@column_name) + '] ' + @data_type + '(' + CAST(@max_length AS nvarchar(100)) +  ') COLLATE ' + @collate + @null
            PRINT @sql
            EXEC sp_executesql @sql
        END TRY
          PRINT 'ERROR: Some index or contraint rely on the column ' + @column_name + '. No conversion possible.'
          PRINT @sql
        END CATCH

        FETCH NEXT FROM local_change_cursor
        INTO @row_id, @column_name, @data_type, @max_length, @column_id, @is_Nullable


    CLOSE local_change_cursor
    DEALLOCATE local_change_cursor

    FETCH NEXT FROM local_table_cursor
    INTO @table


CLOSE local_table_cursor
DEALLOCATE local_table_cursor


How to deselect a selected UITableView cell?

This is a solution for Swift 4

 in tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath)

just add

tableView.deselectRow(at: indexPath, animated: true)

it works like a charm


func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
        tableView.deselectRow(at: indexPath, animated: true)
//some code

Make a directory and copy a file

Use the FileSystemObject object, namely, its CreateFolder and CopyFile methods. Basically, this is what your script will look like:

Dim oFSO
Set oFSO = CreateObject("Scripting.FileSystemObject")

' Create a new folder
oFSO.CreateFolder "C:\MyFolder"

' Copy a file into the new folder
' Note that the destination folder path must end with a path separator (\)
oFSO.CopyFile "\\server\folder\file.ext", "C:\MyFolder\"

You may also want to add additional logic, like checking whether the folder you want to create already exists (because CreateFolder raises an error in this case) or specifying whether or not to overwrite the file being copied. So, you can end up with this:

Const strFolder = "C:\MyFolder\", strFile = "\\server\folder\file.ext"
Const Overwrite = True
Dim oFSO

Set oFSO = CreateObject("Scripting.FileSystemObject")

If Not oFSO.FolderExists(strFolder) Then
  oFSO.CreateFolder strFolder
End If

oFSO.CopyFile strFile, strFolder, Overwrite

How to get row data by clicking a button in a row in an ASP.NET gridview

            <asp:Button  ID="btnEdit" Text="Edit" runat="server"  OnClick="btnEdit_Click" CssClass="CoolButtons"/>

protected void btnEdit_Click(object sender, EventArgs e)
       Button btnEdit = (Button)sender;
       GridViewRow Grow = (GridViewRow)btnEdit.NamingContainer;
      TextBox txtledName = (TextBox)Grow.FindControl("txtAccountName");
      HyperLink HplnkDr = (HyperLink)Grow.FindControl("HplnkDr");
      TextBox txtnarration = (TextBox)Grow.FindControl("txtnarration");
     //Get the gridview Row Details

And Same As for Delete button

What's the net::ERR_HTTP2_PROTOCOL_ERROR about?

In my case I have a kubernetes cluster with nginx ingress controller and nginx+php-fpm to handle drupal instance.

I notice this issue on one of my page, where my pictures was not loaded in chrome. After investigation I discovered that modsecurity module enabled in my nginx ingress somehow produce this issue. Not fully know why, but after disabling it, all pages are loaded fine.

Best Regards.

Make an image follow mouse pointer

Ok, here's a simple box that follows the cursor

Doing the rest is a simple case of remembering the last cursor position and applying a formula to get the box to move other than exactly where the cursor is. A timeout would also be handy if the box has a limited acceleration and must catch up to the cursor after it stops moving. Replacing the box with an image is simple CSS (which can replace most of the setup code for the box). I think the actual thinking code in the example is about 8 lines.

Select the right image (use a sprite) to orientate the rocket.

Yeah, annoying as hell. :-)

function getMouseCoords(e) {
  var e = e || window.event;
  document.getElementById('container').innerHTML = e.clientX + ', ' +
    e.clientY + '<br>' + e.screenX + ', ' + e.screenY;

var followCursor = (function() {
  var s = document.createElement('div'); = 'absolute'; = '0'; = '5px'; = '1px solid red';
  s.textContent = ""

  return {
    init: function() {

    run: function(e) {
      var e = e || window.event; = (e.clientX - 5) + 'px'; = (e.clientY - 5) + 'px';

window.onload = function() {
  document.body.onmousemove =;
#container {
  width: 1000px;
  height: 1000px;
  border: 1px solid blue;
<div id="container"></div>

SQL Server Format Date DD.MM.YYYY HH:MM:SS


How can I add a help method to a shell script?

For a quick single option solution, use if

If you only have a single option to check and it will always be the first option ($1) then the simplest solution is an if with a test ([). For example:

if [ "$1" == "-h" ] ; then
    echo "Usage: `basename $0` [-h]"
    exit 0

Note that for posix compatibility = will work as well as ==.

Why quote $1?

The reason the $1 needs to be enclosed in quotes is that if there is no $1 then the shell will try to run if [ == "-h" ] and fail because == has only been given a single argument when it was expecting two:

$ [ == "-h" ]
bash: [: ==: unary operator expected

For anything more complex use getopt or getopts

As suggested by others, if you have more than a single simple option, or need your option to accept an argument, then you should definitely go for the extra complexity of using getopts.

As a quick reference, I like The 60 second getopts tutorial.

You may also want to consider the getopt program instead of the built in shell getopts. It allows the use of long options, and options after non option arguments (e.g. foo a b c --verbose rather than just foo -v a b c). This Stackoverflow answer explains how to use GNU getopt.

jeffbyrnes mentioned that the original link died but thankfully the way back machine had archived it.

Reliable way to convert a file to a byte[]

looks good enough as a generic version. You can modify it to meet your needs, if they're specific enough.

also test for exceptions and error conditions, such as file doesn't exist or can't be read, etc.

you can also do the following to save some space:

 byte[] bytes = System.IO.File.ReadAllBytes(filename);

Printing reverse of any String without using any predefined function?

Here's a recursive solution that just prints the string in reverse order. It should be educational if you're trying to learn recursion. I've also made it "wrong" by actually having 2 print statements; one of them should be commented out. Try to figure out which mentally, or just run experiments. Either way, learn from it.

static void printReverse(String s) {
    if (!s.isEmpty()) {
        System.out.print(s.substring(0, 1));
        System.out.print(s.substring(0, 1));

Bonus points if you answer these questions:

What is the preferred syntax for defining enums in JavaScript?

Here's what we all want:

function Enum(constantsList) {
    for (var i in constantsList) {
        this[constantsList[i]] = i;

Now you can create your enums:

var YesNo = new Enum(['NO', 'YES']);
var Color = new Enum(['RED', 'GREEN', 'BLUE']);

By doing this, constants can be acessed in the usual way (YesNo.YES, Color.GREEN) and they get a sequential int value (NO = 0, YES = 1; RED = 0, GREEN = 1, BLUE = 2).

You can also add methods, by using Enum.prototype:

Enum.prototype.values = function() {
    return this.allValues;
    /* for the above to work, you'd need to do
            this.allValues = constantsList at the constructor */

Edit - small improvement - now with varargs: (unfortunately it doesn't work properly on IE :S... should stick with previous version then)

function Enum() {
    for (var i in arguments) {
        this[arguments[i]] = i;

var YesNo = new Enum('NO', 'YES');
var Color = new Enum('RED', 'GREEN', 'BLUE');

Margin-Top not working for span element?

Always remember one thing we can not apply margin vertically to inline elements ,if you want to apply then change its display type to block or inline block.for example span{display:inline-block;}

Command failed due to signal: Segmentation fault: 11

Read the debug message carefully.

in my case, I encountered this error because I used a single '=' instead of double '=' by mistake in if-statement.

if aString.characters.count = 2 {...}

What's the difference between echo, print, and print_r in PHP?

The difference between echo, print, print_r and var_dump is very simple.


echo is actually not a function but a language construct which is used to print output. It is marginally faster than the print.

echo "Hello World";    // this will print Hello World
echo "Hello ","World"; // Multiple arguments - this will print Hello World

echo "$var_1";               // this will print 55
echo "var_1=".$var_1;        // this will print var_1=55
echo 45+$var_1;              // this will print 100

echo "$var_2";                   // this will print PHP

$var_3=array(99,98,97)           // Arrays are not possible with echo (loop or index  value required)
$var_4=array("P"=>"3","J"=>"4"); // Arrays are not possible with echo (loop or index  value required)

You can also use echo statement with or without parenthese

echo ("Hello World");   // this will print Hello World


Just like echo construct print is also a language construct and not a real function. The differences between echo and print is that print only accepts a single argument and print always returns 1. Whereas echo has no return value. So print statement can be used in expressions.

print "Hello World";    // this will print Hello World
print "Hello ","World"; // Multiple arguments - NOT POSSIBLE with print
print "$var_1";               // this will print 55
print "var_1=".$var_1;        // this will print var_1=55
print 45+$var_1;              // this will print 100

print "$var_2";                   // this will print PHP

$var_3=array(99,98,97)           // Arrays are not possible with print (loop or index  value required)
$var_4=array("P"=>"3","J"=>"4"); // Arrays are not possible with print (loop or index  value required)

Just like echo, print can be used with or without parentheses.

print ("Hello World");   // this will print Hello World


The print_r() function is used to print human-readable information about a variable. If the argument is an array, print_r() function prints its keys and elements (same for objects).

print_r ("Hello World");    // this will print Hello World

print_r ("$var_1");               // this will print 55
print_r ("var_1=".$var_1);        // this will print var_1=55
print_r (45+$var_1);              // this will print 100

print_r ("$var_2");                // this will print PHP

$var_3=array(99,98,97)             // this will print Array ( [0] => 1 [1] => 2 [2] => 3 ) 
$var_4=array("P"=>"3","J"=>"4");   // this will print  Array ( [P] => 3 [J] => 4 ) 


var_dump function usually used for debugging and prints the information ( type and value) about a variable/array/object.

var_dump($var_1);     // this will print  int(5444) 
var_dump($var_2);     // this will print  string(5) "Hello" 
var_dump($var_3);     // this will print  array(3) { [0]=> int(1) [1]=> int(2) [2]=> int(3) } 
var_dump($var_4);     // this will print  array(2) { ["P"]=> string(1) "3" ["J"]=> string(1) "4" }

Best practices for Storyboard login screen, handling clearing of data upon logout

Here is what I ended up doing to accomplish everything. The only thing you need to consider in addition to this is (a) the login process and (b) where you are storing your app data (in this case, I used a singleton).

Storyboard showing login view controller and main tab controller

As you can see, the root view controller is my Main Tab Controller. I did this because after the user has logged in, I want the app to launch directly to the first tab. (This avoids any "flicker" where the login view shows temporarily.)


In this file, I check whether the user is already logged in. If not, I push the login view controller. I also handle the logout process, where I clear data and show the login view.

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions

    // Show login view if not logged in already
    if(![AppData isLoggedIn]) {
        [self showLoginScreen:NO];

    return YES;

-(void) showLoginScreen:(BOOL)animated

    // Get login screen from storyboard and present it
    UIStoryboard *storyboard = [UIStoryboard storyboardWithName:@"MainStoryboard" bundle:nil];
    LoginViewController *viewController = (LoginViewController *)[storyboard instantiateViewControllerWithIdentifier:@"loginScreen"];
    [self.window makeKeyAndVisible];
    [self.window.rootViewController presentViewController:viewController

-(void) logout
    // Remove data from singleton (where all my app data is stored)
    [AppData clearData];

   // Reset view controller (this will quickly clear all the views)
   UIStoryboard *storyboard = [UIStoryboard storyboardWithName:@"MainStoryboard" bundle:nil];
   MainTabControllerViewController *viewController = (MainTabControllerViewController *)[storyboard instantiateViewControllerWithIdentifier:@"mainView"];
   [self.window setRootViewController:viewController];

   // Show login screen
   [self showLoginScreen:NO];



Here, if the login is successful, I simply dismiss the view and send a notification.

-(void) loginWasSuccessful

     // Send notification
     [[NSNotificationCenter defaultCenter] postNotificationName:@"loginSuccessful" object:self];

     // Dismiss login screen
     [self dismissViewControllerAnimated:YES completion:nil];


Best JavaScript compressor


Kjscompress/csskompress is set of two applications (kjscompress a csscompress) to remove non-significant whitespaces and comments from files containing JavaScript and CSS. Both are command-line applications for GNU/Linux operating system.

Bootstrap 3 offset on right not left

<div class="row col-xs-12">            _x000D_
            <nav class="col-xs-12 col-xs-offset-7" aria-label="Page navigation">_x000D_
                <ul class="pagination mt-0">                   _x000D_
                    <li class="page-item">                        _x000D_
                        <div class="form-group">_x000D_
                            <div class="input-group">_x000D_
                                <input type="text" asp-for="search" class="form-control" placeholder="Search" aria-controls="order-listing" />_x000D_
                                <div class="input-group-prepend bg-info">_x000D_
                                    <input type="submit" value="Search" class="input-group-text bg-transparent">                                   _x000D_

Counting the number of non-NaN elements in a numpy ndarray in Python


~ inverts the boolean matrix returned from np.isnan.

np.count_nonzero counts values that is not 0\false. .sum should give the same result. But maybe more clearly to use count_nonzero

Testing speed:

In [23]: data = np.random.random((10000,10000))

In [24]: data[[np.random.random_integers(0,10000, 100)],:][:, [np.random.random_integers(0,99, 100)]] = np.nan

In [25]: %timeit data.size - np.count_nonzero(np.isnan(data))
1 loops, best of 3: 309 ms per loop

In [26]: %timeit np.count_nonzero(~np.isnan(data))
1 loops, best of 3: 345 ms per loop

In [27]: %timeit data.size - np.isnan(data).sum()
1 loops, best of 3: 339 ms per loop

data.size - np.count_nonzero(np.isnan(data)) seems to barely be the fastest here. other data might give different relative speed results.

How do I get the HTTP status code with jQuery?

I think you should also implement the error function of the $.ajax method.

error(XMLHttpRequest, textStatus, errorThrown)Function

A function to be called if the request fails. The function is passed three arguments: The XMLHttpRequest object, a string describing the type of error that occurred and an optional exception object, if one occurred. Possible values for the second argument (besides null) are "timeout", "error", "notmodified" and "parsererror".

    url: "http://my-ip/test/test.php",
    data: {},
    complete: function(xhr, statusText){
    error: function(xhr, statusText, err){
        alert("Error:" + xhr.status); 

Calling dynamic function with dynamic number of parameters

function a(a, b) {
    return a + b

function call_a() {
    return a.apply(a,, 0));

console.log(call_a(1, 2))

console: 3

Step-by-step debugging with IPython

What about ipdb.set_trace() ? In your code :

import ipdb; ipdb.set_trace()

update: now in Python 3.7, we can write breakpoint(). It works the same, but it also obeys to the PYTHONBREAKPOINT environment variable. This feature comes from this PEP.

This allows for full inspection of your code, and you have access to commands such as c (continue), n (execute next line), s (step into the method at point) and so on.

See the ipdb repo and a list of commands. IPython is now called (edit: part of) Jupyter.

ps: note that an ipdb command takes precedence over python code. So in order to write list(foo) you'd need print(list(foo)), or !list(foo) .

Also, if you like the ipython prompt (its emacs and vim modes, history, completions,…) it's easy to get the same for your project since it's based on the python prompt toolkit.

Can I extend a class using more than 1 class in PHP?

PHP does not allow multiple inheritance, but you can do with implementing multiple interfaces. If the implementation is "heavy", provide skeletal implementation for each interface in a seperate class. Then, you can delegate all interface class to these skeletal implementations via object containment.

Show div when radio button selected

Input elements should have value attributes. Add them and use this:

$("input[name='test']").click(function () {
    $('#show-me').css('display', ($(this).val() === 'a') ? 'block':'none');

jsFiddle example

Why doesn't Dijkstra's algorithm work for negative weight edges?

Correctness of Dijkstra's algorithm:

We have 2 sets of vertices at any step of the algorithm. Set A consists of the vertices to which we have computed the shortest paths. Set B consists of the remaining vertices.

Inductive Hypothesis: At each step we will assume that all previous iterations are correct.

Inductive Step: When we add a vertex V to the set A and set the distance to be dist[V], we must prove that this distance is optimal. If this is not optimal then there must be some other path to the vertex V that is of shorter length.

Suppose this some other path goes through some vertex X.

Now, since dist[V] <= dist[X] , therefore any other path to V will be atleast dist[V] length, unless the graph has negative edge lengths.

Thus for dijkstra's algorithm to work, the edge weights must be non negative.

Where's the DateTime 'Z' format specifier?

Maybe the "K" format specifier would be of some use. This is the only one that seems to mention the use of capital "Z".

"Z" is kind of a unique case for DateTimes. The literal "Z" is actually part of the ISO 8601 datetime standard for UTC times. When "Z" (Zulu) is tacked on the end of a time, it indicates that that time is UTC, so really the literal Z is part of the time. This probably creates a few problems for the date format library in .NET, since it's actually a literal, rather than a format specifier.

The Use of Multiple JFrames: Good or Bad Practice?

I'd like to counter the "not user friendly" argument with an example that I have just been involved with.

In our application we have a main window where the users run various 'programs' as separate tabs. As much as possible we have tried to keep our application to this single window.

One of the 'programs' they run presents a list of reports that have been generated by the system, and the user can click on an icon on each line to pop open a report viewer dialog. This viewer is showing the equivalent of the portrait/landscape A4 page(s) of the report, so the users like this window to be quite big, almost filling their screens.

A few months ago we started getting requests from our customers to make these report viewer windows modeless, so that they could have multiple reports open at the same time.

For some time I resisted this request as I did not think this was a good solution. However, my mind was changed when I found out how the users were getting around this 'deficiency' of our system.

They were opening a viewer, using the 'Save As' facility to save the report as a PDF to a specific directory, using Acrobat Reader to open the PDF file, and then they would do the same with the next report. They would have multiple Acrobat Readers running with the various report outputs that they wanted to look at.

So I relented and made the viewer modeless. This means that each viewer has a task-bar icon.

When the latest version was released to them last week, the overwhelming response from them is that they LOVE it. It's been one of our most popular recent enhancements to the system.

So you go ahead and tell your users that what they want is bad, but ultimately it won't do you any favours.


  • It seems to be best practice to use JDialog's for these modeless windows
  • Use the constructors that use the new ModalityType rather than the boolean modal argument. This is what gives these dialogs the task-bar icon.
  • For modeless dialogs, pass a null parent to the constructor, but locate them relative to their 'parent' window.
  • Version 6 of Java on Windows has a bug which means that your main window can become 'always on top' without you telling it. Upgrade to version 7 to fix this

How to add a list item to an existing unordered list?

This is the shortest way you can do that

list.push($('<li>', {text: blocks[i] }));

Where blocks in an array. and you need to loop through the array.

Stop an input field in a form from being submitted

I just wanted to add an additional option: In your input add the form tag and specify the name of a form that doesn't exist on your page:

<input form="fakeForm" type="text" readonly value="random value" />

Update just one gem with bundler

The way to do this is to run the following command:

bundle update --source gem-name

Creating the checkbox dynamically using JavaScript?

You can create a function:

function changeInputType(oldObj, oTyp, nValue) {
  var newObject = document.createElement('input');
  newObject.type = oTyp;
  if(oldObj.size) newObject.size = oldObj.size;
  if(oldObj.value) newObject.value = nValue;
  if( =;
  if( =;
  if(oldObj.className) newObject.className = oldObj.className;
  return newObject;

And you do a call like:

changeInputType(document.getElementById('DATE_RANGE_VALUE'), 'checkbox', 7);

Case-insensitive search

There are two ways for case insensitive comparison:

  1. Convert strings to upper case and then compare them using the strict operator (===). How strict operator treats operands read stuff at:

  2. Pattern matching using string methods:

    Use the "search" string method for case insensitive search. Read about search and other string methods at:

    <!doctype html>
            // 1st way
            var a = "apple";
            var b = "APPLE";  
            if (a.toUpperCase() === b.toUpperCase()) {
            //2nd way
            var a = " Null and void";

How to check for Is not Null And Is not Empty string in SQL server?

in basic way

FROM [TableName]
WHERE column_name!='' AND column_name IS NOT NULL

How to retrieve element value of XML using Java?

There are two general ways of doing that. You will either create a Domain Object Model of that XML file, take a look at this

and the second choice is using event driven parsing, which is an alternative to DOM xml representation. Imho you can find the best overall comparison of these two basic techniques here. Of course there are much more to know about processing xml, for instance if you are given XML schema definition (XSD), you could use JAXB.

TypeError: 'dict_keys' object does not support indexing

Why you need to implement shuffle when it already exists? Stay on the shoulders of giants.

import random

d1 = {0:'zero', 1:'one', 2:'two', 3:'three', 4:'four',
     5:'five', 6:'six', 7:'seven', 8:'eight', 9:'nine'}

keys = list(d1)

d2 = {}
for key in keys: d2[key] = d1[key]


How to convert a selection to lowercase or uppercase in Sublime Text

For Windows OS

For Uppercase CTRL + K + U

For Lowercase CTRL + K + L

How do I write a SQL query for a specific date range and date time using SQL Server 2008?

Remember that the US date format is different from the UK. Using the UK format, it needs to be, e.g.

--                                  dd/mm/ccyy hh:mm:ss     
dbo.no_time(at.date_stamp) between '22/05/2016 00:00:01' and '22/07/2016 23:59:59' 

How do I enable TODO/FIXME/XXX task tags in Eclipse?

For me, such tags are enabled by default. You can configure which task tags should be used in the workspace options: Java > Compiler > Task tags

alt text

Check if they are enabled in this location, and that should be enough to have them appear in the Task list (or the Markers view).

Extra note: reinstalling Eclipse won't change anything most of the time if you work on the same workspace. Most settings used by Eclipse are stored in the .metadata folder, in your workspace folder.

Declaring functions in JSP?

You need to enclose that in <%! %> as follows:


public String getQuarter(int i){
String quarter;
        case 1: quarter = "Winter";

        case 2: quarter = "Spring";

        case 3: quarter = "Summer I";

        case 4: quarter = "Summer II";

        case 5: quarter = "Fall";

        default: quarter = "ERROR";

return quarter;


You can then invoke the function within scriptlets or expressions:



<%= getQuarter(17) %>

Connection string using Windows Authentication

For the correct solution after many hours:

  1. Open the configuration file
  2. Change the connection string with the following

<add name="umbracoDbDSN" connectionString="data source=YOUR_SERVER_NAME;database=nrc;Integrated Security=SSPI;persist security info=True;" providerName="System.Data.SqlClient" />

  1. Change the YOUR_SERVER_NAME with your current server name and save
  2. Open the IIS Manager
  3. Find the name of the application pool that the website or web application is using
  4. Right-click and choose Advanced settings
  5. From Advanced settings under Process Model change the Identity to Custom account and add your Server Admin details, please see the attached images:

enter image description here

Hope this will help.

How set the android:gravity to TextView from Java side in Android

Solved this by doing a few things, first getting the height of my TextView and diving it by the text size to get the total amount of lines possible with the TextView.

int maxLines = (int) TextView.getHeight() / (int) TextView.getTextSize();

After you get this value you need to set your TextView maxLines to this new value.


Set the Gravity to Bottom once the maximum amount of lines has been exceeded and it will scroll down automatically.

if (TextView.getLineCount() >= maxLines) {

In order for this to work correctly, you must use append() to the TextView, If you setText() this will not work.

TextView.append("Your Text");

The benefit of this method is that this can be used dynamically regardless of the height of your TextView and the text size. If you decide to make modifications to your layout this code would still work.

MySQL limit from descending order

This way is comparatively more easy

SELECT doc_id,serial_number,status FROM date_time ORDER BY  date_time DESC LIMIT 0,1;

Override valueof() and toString() in Java enum

The following is a nice generic alternative to valueOf()

public static RandomEnum getEnum(String value) {
  for (RandomEnum re : RandomEnum.values()) {
    if (re.description.compareTo(value) == 0) {
      return re;
  throw new IllegalArgumentException("Invalid RandomEnum value: " + value);

Creating SolidColorBrush from hex color value

How to get Color from Hexadecimal color code using .NET?

This I think is what you are after, hope it answers your question.

To get your code to work use Convert.ToByte instead of Convert.ToInt...

string colour = "#ffaacc";


android pick images from gallery

If you are only looking for images and multiple selection.

Look @ once

It's helpful for future.I personally feel great by using MultipleImagePick.

How to validate an Email in PHP?

This is old post but I will share one my solution because noone mention here one problem before.

New email address can contain UTF-8 characters or special domain names like .live, .news etc.

Also I find that some email address can be on Cyrilic and on all cases standard regex or filter_var() will fail.

That's why I made an solution for it:

function valid_email($email) 
    if(is_array($email) || is_numeric($email) || is_bool($email) || is_float($email) || is_file($email) || is_dir($email) || is_int($email))
        return false;
        if(filter_var($email, FILTER_VALIDATE_EMAIL)!==false) return $email;
            $pattern = '/^(?!(?:(?:\\x22?\\x5C[\\x00-\\x7E]\\x22?)|(?:\\x22?[^\\x5C\\x22]\\x22?)){255,})(?!(?:(?:\\x22?\\x5C[\\x00-\\x7E]\\x22?)|(?:\\x22?[^\\x5C\\x22]\\x22?)){65,}@)(?:(?:[\\x21\\x23-\\x27\\x2A\\x2B\\x2D\\x2F-\\x39\\x3D\\x3F\\x5E-\\x7E]+)|(?:\\x22(?:[\\x01-\\x08\\x0B\\x0C\\x0E-\\x1F\\x21\\x23-\\x5B\\x5D-\\x7F]|(?:\\x5C[\\x00-\\x7F]))*\\x22))(?:\\.(?:(?:[\\x21\\x23-\\x27\\x2A\\x2B\\x2D\\x2F-\\x39\\x3D\\x3F\\x5E-\\x7E]+)|(?:\\x22(?:[\\x01-\\x08\\x0B\\x0C\\x0E-\\x1F\\x21\\x23-\\x5B\\x5D-\\x7F]|(?:\\x5C[\\x00-\\x7F]))*\\x22)))*@(?:(?:(?!.*[^.]{64,})(?:(?:(?:xn--)?[a-z0-9]+(?:-+[a-z0-9]+)*\\.){1,126}){1,}(?:(?:[a-z][a-z0-9]*)|(?:(?:xn--)[a-z0-9]+))(?:-+[a-z0-9]+)*)|(?:\\[(?:(?:IPv6:(?:(?:[a-f0-9]{1,4}(?::[a-f0-9]{1,4}){7})|(?:(?!(?:.*[a-f0-9][:\\]]){7,})(?:[a-f0-9]{1,4}(?::[a-f0-9]{1,4}){0,5})?::(?:[a-f0-9]{1,4}(?::[a-f0-9]{1,4}){0,5})?)))|(?:(?:IPv6:(?:(?:[a-f0-9]{1,4}(?::[a-f0-9]{1,4}){5}:)|(?:(?!(?:.*[a-f0-9]:){5,})(?:[a-f0-9]{1,4}(?::[a-f0-9]{1,4}){0,3})?::(?:[a-f0-9]{1,4}(?::[a-f0-9]{1,4}){0,3}:)?)))?(?:(?:25[0-5])|(?:2[0-4][0-9])|(?:1[0-9]{2})|(?:[1-9]?[0-9]))(?:\\.(?:(?:25[0-5])|(?:2[0-4][0-9])|(?:1[0-9]{2})|(?:[1-9]?[0-9]))){3}))\\]))$/iD';
            return (preg_match($pattern, $email) === 1) ? $email : false;

This function work perfectly for all cases and email formats.

WARNING in budgets, maximum exceeded for initial

What is Angular CLI Budgets? Budgets is one of the less known features of the Angular CLI. It’s a rather small but a very neat feature!

As applications grow in functionality, they also grow in size. Budgets is a feature in the Angular CLI which allows you to set budget thresholds in your configuration to ensure parts of your application stay within boundaries which you setOfficial Documentation

Or in other words, we can describe our Angular application as a set of compiled JavaScript files called bundles which are produced by the build process. Angular budgets allows us to configure expected sizes of these bundles. More so, we can configure thresholds for conditions when we want to receive a warning or even fail build with an error if the bundle size gets too out of control!

How To Define A Budget? Angular budgets are defined in the angular.json file. Budgets are defined per project which makes sense because every app in a workspace has different needs.

Thinking pragmatically, it only makes sense to define budgets for the production builds. Prod build creates bundles with “true size” after applying all optimizations like tree-shaking and code minimization.

Oops, a build error! The maximum bundle size was exceeded. This is a great signal that tells us that something went wrong…

  1. We might have experimented in our feature and didn’t clean up properly
  2. Our tooling can go wrong and perform a bad auto-import, or we pick bad item from the suggested list of imports
  3. We might import stuff from lazy modules in inappropriate locations
  4. Our new feature is just really big and doesn’t fit into existing budgets

First Approach: Are your files gzipped?

Generally speaking, gzipped file has only about 20% the size of the original file, which can drastically decrease the initial load time of your app. To check if you have gzipped your files, just open the network tab of developer console. In the “Response Headers”, if you should see “Content-Encoding: gzip”, you are good to go.

How to gzip? If you host your Angular app in most of the cloud platforms or CDN, you should not worry about this issue as they probably have handled this for you. However, if you have your own server (such as NodeJS + expressJS) serving your Angular app, definitely check if the files are gzipped. The following is an example to gzip your static assets in a NodeJS + expressJS app. You can hardly imagine this dead simple middleware “compression” would reduce your bundle size from 2.21MB to 495.13KB.

const compression = require('compression')
const express = require('express')
const app = express()

Second Approach:: Analyze your Angular bundle

If your bundle size does get too big you may want to analyze your bundle because you may have used an inappropriate large-sized third party package or you forgot to remove some package if you are not using it anymore. Webpack has an amazing feature to give us a visual idea of the composition of a webpack bundle.

enter image description here

It’s super easy to get this graph.

  1. npm install -g webpack-bundle-analyzer
  2. In your Angular app, run ng build --stats-json (don’t use flag --prod). By enabling --stats-json you will get an additional file stats.json
  3. Finally, run webpack-bundle-analyzer ./dist/stats.json and your browser will pop up the page at localhost:8888. Have fun with it.

ref 1: How Did Angular CLI Budgets Save My Day And How They Can Save Yours

ref 2: Optimize Angular bundle size in 4 steps

Unstage a deleted file in git

Assuming you're wanting to undo the effects of git rm <file> or rm <file> followed by git add -A or something similar:

# this restores the file status in the index
git reset -- <file>
# then check out a copy from the index
git checkout -- <file>

To undo git add <file>, the first line above suffices, assuming you haven't committed yet.

Warnings Your Apk Is Using Permissions That Require A Privacy Policy: (android.permission.READ_PHONE_STATE)

See steb by step and you will understood

public static String getVideoTitle(String youtubeVideoUrl) {
        Log.e(youtubeVideoUrl.toString() + " In GetVideoTitle Menu".toString() ,"hiii" );
        try {

            if (youtubeVideoUrl != null) {
                URL embededURL = new URL("" +
                        youtubeVideoUrl + "&format=json"
                Log.e(youtubeVideoUrl.toString() + " In EmbedJson Try Function ".toString() ,"hiii" );
                Log.e(embededURL.toString() + " In EmbedJson Retrn value ".toString() ,"hiii" );
                Log.e(new JSONObject(IOUtils.toString(embededURL)).getString("provider_name").toString() + " In EmbedJson Retrn value ".toString() ,"hiii" );

                return new JSONObject(IOUtils.toString(embededURL)).getString("provider_name").toString();
        } catch (Exception e) {
            Log.e(" In catch Function ".toString() ,"hiii" );

        return null;