Programs & Examples On #Multiple inheritance

A feature of some object-oriented computer programming languages in which a class can inherit behaviors and features from more than one superclass or base class.

Class extending more than one class Java?

In Java multiple inheritance is not permitted. It was excluded from the language as a design decision, primarily to avoid circular dependencies.

Scenario1: As you have learned the following is not possible in Java:

public class Dog extends Animal, Canine{


Scenario 2: However the following is possible:

public class Canine extends Animal{


public class Dog extends Canine{


The difference in these two approaches is that in the second approach there is a clearly defined parent or super class, while in the first approach the super class is ambiguous.

Consider if both Animal and Canine had a method drink(). Under the first scenario which parent method would be called if we called Dog.drink()? Under the second scenario, we know calling Dog.drink() would call the Canine classes drink method as long as Dog had not overridden it.

Can one class extend two classes?

Java doesn't support multiple inheritance. You can implement multiple interfaces, but not extend multiple classes.

Multiple Inheritance in C#

We all seem to be heading down the interface path with this, but the obvious other possibility, here, is to do what OOP is supposed to do, and build up your inheritance tree... (isn't this what class design is all about?)

class Program
    static void Main(string[] args)
        human me = new human();
        me.legs = 2;
        me.lfType = "Human"; = "Paul";

public abstract class lifeform
    public string lfType { get; set; }

public abstract class mammal : lifeform 
    public int legs { get; set; }

public class human : mammal
    public string name { get; set; }

This structure provides reusable blocks of code and, surely, is how OOP code should be written?

If this particular approach doesn't quite fit the bill the we simply create new classes based on the required objects...

class Program
    static void Main(string[] args)
        fish shark = new fish();
        shark.size = "large";
        shark.lfType = "Fish"; = "Jaws";
        human me = new human();
        me.legs = 2;
        me.lfType = "Human"; = "Paul";

public abstract class lifeform
    public string lfType { get; set; }

public abstract class mammal : lifeform 
    public int legs { get; set; }

public class human : mammal
    public string name { get; set; }

public class aquatic : lifeform
    public string size { get; set; }

public class fish : aquatic
    public string name { get; set; }

Can a normal Class implement multiple interfaces?

In a word - yes. Actually, many classes in the JDK implement multiple interfaces. E.g., ArrayList implements List, RandomAccess, Cloneable, and Serializable.

Java Multiple Inheritance

In Java 8, which is still in the development phase as of February 2014, you could use default methods to achieve a sort of C++-like multiple inheritance. You could also have a look at this tutorial which shows a few examples that should be easier to start working with than the official documentation.

Can an interface extend multiple interfaces in Java?

You can extend multiple Interfaces but you cannot extend multiple classes.

The reason that it is not possible in Java to extending multiple classes, is the bad experience from C++ where this is possible.

The alternative for multipe inheritance is that a class can implement multiple interfaces (or an Interface can extend multiple Interfaces)

Does C# support multiple inheritance?

Like Java (which is what C# was indirectly derived from), C# does not support multiple inhertance.

Which is to say that class data (member variables and properties) can only be inherited from a single parent base class. Class behavior (member methods), on the other hand, can be inherited from multiple parent base interfaces.

Some experts, notably Bertrand Meyer (considered by some to be one of the fathers of object-oreiented programming), think that this disqualifies C# (and Java, and all the rest) from being a "true" object-oriented language.

What does 'super' do in Python?

Doesn't all of this assume that the base class is a new-style class?

class A:
    def __init__(self):

class B(A):
    def __init__(self):
        super(B, self).__init__()

Will not work in Python 2. class A must be new-style, i.e: class A(object)

Multiple inheritance for an anonymous class

An anonymous class usually implements an interface:

new Runnable() { // implements Runnable!
   public void run() {}

JFrame.addWindowListener( new WindowAdapter() { // extends  class
} );

If you mean whether you can implement 2 or more interfaces, than I think that's not possible. You can then make a private interface which combines the two. Though I cannot easily imagine why you would want an anonymous class to have that:

 public class MyClass {
   private interface MyInterface extends Runnable, WindowListener { 

   Runnable r = new MyInterface() {
    // your anonymous class which implements 2 interaces


How does Python's super() work with multiple inheritance?

This is detailed with a reasonable amount of detail by Guido himself in his blog post Method Resolution Order (including two earlier attempts).

In your example, Third() will call First.__init__. Python looks for each attribute in the class's parents as they are listed left to right. In this case, we are looking for __init__. So, if you define

class Third(First, Second):

Python will start by looking at First, and, if First doesn't have the attribute, then it will look at Second.

This situation becomes more complex when inheritance starts crossing paths (for example if First inherited from Second). Read the link above for more details, but, in a nutshell, Python will try to maintain the order in which each class appears on the inheritance list, starting with the child class itself.

So, for instance, if you had:

class First(object):
    def __init__(self):
        print "first"

class Second(First):
    def __init__(self):
        print "second"

class Third(First):
    def __init__(self):
        print "third"

class Fourth(Second, Third):
    def __init__(self):
        super(Fourth, self).__init__()
        print "that's it"

the MRO would be [Fourth, Second, Third, First].

By the way: if Python cannot find a coherent method resolution order, it'll raise an exception, instead of falling back to behavior which might surprise the user.

Edited to add an example of an ambiguous MRO:

class First(object):
    def __init__(self):
        print "first"

class Second(First):
    def __init__(self):
        print "second"

class Third(First, Second):
    def __init__(self):
        print "third"

Should Third's MRO be [First, Second] or [Second, First]? There's no obvious expectation, and Python will raise an error:

TypeError: Error when calling the metaclass bases
    Cannot create a consistent method resolution order (MRO) for bases Second, First

Edit: I see several people arguing that the examples above lack super() calls, so let me explain: The point of the examples is to show how the MRO is constructed. They are not intended to print "first\nsecond\third" or whatever. You can – and should, of course, play around with the example, add super() calls, see what happens, and gain a deeper understanding of Python's inheritance model. But my goal here is to keep it simple and show how the MRO is built. And it is built as I explained:

>>> Fourth.__mro__
(<class '__main__.Fourth'>,
 <class '__main__.Second'>, <class '__main__.Third'>,
 <class '__main__.First'>,
 <type 'object'>)

What is a mixin, and why are they useful?

This answer aims to explain mixins with examples that are:

  • self-contained: short, with no need to know any libraries to understand the example.

  • in Python, not in other languages.

    It is understandable that there were examples from other languages such as Ruby since the term is much more common in those languages, but this is a Python thread.

It shall also consider the controversial question:

Is multiple inheritance necessary or not to characterize a mixin?


I have yet to see a citation from an "authoritative" source clearly saying what is a mixin in Python.

I have seen 2 possible definitions of a mixin (if they are to be considered as different from other similar concepts such as abstract base classes), and people don't entirely agree on which one is correct.

The consensus may vary between different languages.

Definition 1: no multiple inheritance

A mixin is a class such that some method of the class uses a method which is not defined in the class.

Therefore the class is not meant to be instantiated, but rather serve as a base class. Otherwise the instance would have methods that cannot be called without raising an exception.

A constraint which some sources add is that the class may not contain data, only methods, but I don't see why this is necessary. In practice however, many useful mixins don't have any data, and base classes without data are simpler to use.

A classic example is the implementation of all comparison operators from only <= and ==:

class ComparableMixin(object):
    """This class has methods which use `<=` and `==`,
    but this class does NOT implement those methods."""
    def __ne__(self, other):
        return not (self == other)
    def __lt__(self, other):
        return self <= other and (self != other)
    def __gt__(self, other):
        return not self <= other
    def __ge__(self, other):
        return self == other or self > other

class Integer(ComparableMixin):
    def __init__(self, i):
        self.i = i
    def __le__(self, other):
        return self.i <= other.i
    def __eq__(self, other):
        return self.i == other.i

assert Integer(0) <  Integer(1)
assert Integer(0) != Integer(1)
assert Integer(1) >  Integer(0)
assert Integer(1) >= Integer(1)

# It is possible to instantiate a mixin:
o = ComparableMixin()
# but one of its methods raise an exception:
#o != o 

This particular example could have been achieved via the functools.total_ordering() decorator, but the game here was to reinvent the wheel:

import functools

class Integer(object):
    def __init__(self, i):
        self.i = i
    def __le__(self, other):
        return self.i <= other.i
    def __eq__(self, other):
        return self.i == other.i

assert Integer(0) < Integer(1)
assert Integer(0) != Integer(1)
assert Integer(1) > Integer(0)
assert Integer(1) >= Integer(1)

Definition 2: multiple inheritance

A mixin is a design pattern in which some method of a base class uses a method it does not define, and that method is meant to be implemented by another base class, not by the derived like in Definition 1.

The term mixin class refers to base classes which are intended to be used in that design pattern (TODO those that use the method, or those that implement it?)

It is not easy to decide if a given class is a mixin or not: the method could be just implemented on the derived class, in which case we're back to Definition 1. You have to consider the author's intentions.

This pattern is interesting because it is possible to recombine functionalities with different choices of base classes:

class HasMethod1(object):
    def method(self):
        return 1

class HasMethod2(object):
    def method(self):
        return 2

class UsesMethod10(object):
    def usesMethod(self):
        return self.method() + 10

class UsesMethod20(object):
    def usesMethod(self):
        return self.method() + 20

class C1_10(HasMethod1, UsesMethod10): pass
class C1_20(HasMethod1, UsesMethod20): pass
class C2_10(HasMethod2, UsesMethod10): pass
class C2_20(HasMethod2, UsesMethod20): pass

assert C1_10().usesMethod() == 11
assert C1_20().usesMethod() == 21
assert C2_10().usesMethod() == 12
assert C2_20().usesMethod() == 22

# Nothing prevents implementing the method
# on the base class like in Definition 1:

class C3_10(UsesMethod10):
    def method(self):
        return 3

assert C3_10().usesMethod() == 13

Authoritative Python occurrences

At the official documentatiton for the documentation explicitly uses the term Mixin Methods.

It states that if a class:

  • implements __next__
  • inherits from a single class Iterator

then the class gets an __iter__ mixin method for free.

Therefore at least on this point of the documentation, mixin does not not require multiple inheritance, and is coherent with Definition 1.

The documentation could of course be contradictory at different points, and other important Python libraries might be using the other definition in their documentation.

This page also uses the term Set mixin, which clearly suggests that classes like Set and Iterator can be called Mixin classes.

In other languages

  • Ruby: Clearly does not require multiple inheritance for mixin, as mentioned in major reference books such as Programming Ruby and The Ruby programming Language

  • C++: A virtual method that is set =0 is a pure virtual method.

    Definition 1 coincides with the definition of an abstract class (a class that has a pure virtual method). That class cannot be instantiated.

    Definition 2 is possible with virtual inheritance: Multiple Inheritance from two derived classes

Appending items to a list of lists in python

Python lists are mutable objects and here:

plot_data = [[]] * len(positions) 

you are repeating the same list len(positions) times.

>>> plot_data = [[]] * 3
>>> plot_data
[[], [], []]
>>> plot_data[0].append(1)
>>> plot_data
[[1], [1], [1]]

Each list in your list is a reference to the same object. You modify one, you see the modification in all of them.

If you want different lists, you can do this way:

plot_data = [[] for _ in positions]

for example:

>>> pd = [[] for _ in range(3)]
>>> pd
[[], [], []]
>>> pd[0].append(1)
>>> pd
[[1], [], []]

- java.lang.NullPointerException - setText on null object reference

Here lies your problem:

private void fillTextView (int id, String text) {
    TextView tv = (TextView) findViewById(id);
    tv.setText(text); // tv is null

--> (TextView) findViewById(id); // returns null But from your code, I can't find why this method returns null. Try to track down, what id you give as a parameter and if this view with the specified id exists.

The error message is very clear and even tells you at what method. From the documentation:

public final View findViewById (int id)
    Look for a child view with the given id. If this view has the given id, return this view.
        id  The id to search for.
        The view that has the given id in the hierarchy or null

In other words: You have no view with the id you give as a parameter.

How can I get the value of a registry key from within a batch script?

For some reason Patrick Cuff's code doesn't work on my system (Windows 7) probably due to tryingToBeClever's comment. Modifying it a little did the trick:

@echo OFF

set KEY_NAME=HKEY_CURRENT_USER\Software\Microsoft\Command Processor
set VALUE_NAME=DefaultColor

FOR /F "tokens=1-3" %%A IN ('REG QUERY %KEY_NAME% /v %VALUE_NAME% 2^>nul') DO (
    set ValueName=%%A
    set ValueType=%%B
    set ValueValue=%%C

if defined ValueName (
    @echo Value Name = %ValueName%
    @echo Value Type = %ValueType%
    @echo Value Value = %ValueValue%
) else (
    @echo %KEY_NAME%\%VALUE_NAME% not found.

Python sys.argv lists and indexes

let's say on the command-line you have:

C:\> C:\Documents and Settings\fred\My Documents\Downloads\google-python-exercises
\google-python-exercises\ John

to make it easier to read, let's just shorten this to:

C:\> John

argv represents all the items that come along via the command-line input, but counting starts at zero (0) not one (1): in this case, "" is element 0, "John" is element 1

in other words, sys.argv[0] == '' and sys.argv[1] == 'John' ... but look, how many elements is this? 2, right! so even though the numbers are 0 and 1, there are 2 elements here.

len(sys.argv) >= 2 just checks whether you entered at least two elements. in this case, we entered exactly 2.

now let's translate your code into English:

define main() function:
    if there are at least 2 elements on the cmd-line:
        set 'name' to the second element located at index 1, e.g., John
    otherwise there is only 1 element... the program name, e.g.,
        set 'name' to "World" (since we did not get any useful user input)
    display 'Hello' followed by whatever i assigned to 'name'

so what does this mean? it means that if you enter:

  • "", the code outputs "Hello World" because you didn't give a name
  • " John", the code outputs "Hello John" because you did
  • " John Paul", the code still outputs "Hello John" because it does not save nor use sys.argv[2], which was "Paul" -- can you see in this case that len(sys.argv) == 3 because there are 3 elements in the sys.argv list?

Stylesheet not updating

First, try to Force reload or Clear cache and Empty chase and hard reload. You can do it by pressing F12 and then by right-clicking on it.

2nd Solution: Check your HTML base tag. You can learn more about it from here.

What do parentheses surrounding an object/function/class declaration mean?

Andy Hume pretty much gave the answer, I just want to add a few more details.

With this construct you are creating an anonymous function with its own evaluation environment or closure, and then you immediately evaluate it. The nice thing about this is that you can access the variables declared before the anonymous function, and you can use local variables inside this function without accidentally overwriting an existing variable.

The use of the var keyword is very important, because in JavaScript every variable is global by default, but with the keyword you create a new, lexically scoped variable, that is, it is visible by the code between the two braces. In your example, you are essentially creating short aliases to the objects in the YUI library, but it has more powerful uses.

I don't want to leave you without a code example, so I'll put here a simple example to illustrate a closure:

var add_gen = function(n) {
  return function(x) {
    return n + x;
var add2 = add_gen(2);
add2(3); // result is 5

What is going on here? In the function add_gen you are creating an another function which will simply add the number n to its argument. The trick is that in the variables defined in the function parameter list act as lexically scoped variables, like the ones defined with var.

The returned function is defined between the braces of the add_gen function so it will have access to the value of n even after add_gen function has finished executing, that is why you will get 5 when executing the last line of the example.

With the help of function parameters being lexically scoped, you can work around the "problems" arising from using loop variables in anonymous functions. Take a simple example:

for(var i=0; i<5; i++) {
  setTimeout(function(){alert(i)}, 10);

The "expected" result could be the numbers from zero to four, but you get four instances of fives instead. This happens because the anonymous function in setTimeout and the for loop are using the very same i variable, so by the time the functions get evaluated, i will be 5.

You can get the naively expected result by using the technique in your question and the fact, that function parameters are lexically scoped. (I've used this approach in an other answer)

for(var i=0; i<5; i++) {
     (function(j) {
       return function(){alert(j)};
     })(i), 10);

With the immediate evaluation of the outer function you are creating a completely independent variable named j in each iteration, and the current value of i will be copied in to this variable, so you will get the result what was naively expected from the first try.

I suggest you to try to understand the excellent tutorial at to understand closures better, that is where I learnt very-very much.

paint() and repaint() in Java

It's not necessary to call repaint unless you need to render something specific onto a component. "Something specific" meaning anything that isn't provided internally by the windowing toolkit you're using.

What are Bearer Tokens and token_type in OAuth 2?

Anyone can define "token_type" as an OAuth 2.0 extension, but currently "bearer" token type is the most common one.

Basically that's what Facebook is using. Their implementation is a bit behind from the latest spec though.

If you want to be more secure than Facebook (or as secure as OAuth 1.0 which has "signature"), you can use "mac" token type.

However, it will be hard way since the mac spec is still changing rapidly.

httpd Server not started: (13)Permission denied: make_sock: could not bind to address [::]:88

At terminal run this command with root permission:

sudo /etc/init.d/apache2 start

You must be root for starting a webserver otherwise you would get similar error.

Mapping a JDBC ResultSet to an object

Complete solution using @TEH-EMPRAH ideas and Generic casting from Cast Object to Generic Type for returning

import annotations.Column;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.sql.SQLException;
import java.util.*;

public class ObjectMapper<T> {

    private Class clazz;
    private Map<String, Field> fields = new HashMap<>();
    Map<String, String> errors = new HashMap<>();

    public DataMapper(Class clazz) {
        this.clazz = clazz;

        List<Field> fieldList = Arrays.asList(clazz.getDeclaredFields());
        for (Field field : fieldList) {
            Column col = field.getAnnotation(Column.class);
            if (col != null) {
                fields.put(, field);

    public T map(Map<String, Object> row) throws SQLException {
        try {
            T dto = (T) clazz.getConstructor().newInstance();
            for (Map.Entry<String, Object> entity : row.entrySet()) {
                if (entity.getValue() == null) {
                    continue;  // Don't set DBNULL
                String column = entity.getKey();
                Field field = fields.get(column);
                if (field != null) {
                    field.set(dto, convertInstanceOfObject(entity.getValue()));
            return dto;
        } catch (IllegalAccessException | InstantiationException | NoSuchMethodException | InvocationTargetException e) {
            throw new SQLException("Problem with data Mapping. See logs.");

    public List<T> map(List<Map<String, Object>> rows) throws SQLException {
        List<T> list = new LinkedList<>();

        for (Map<String, Object> row : rows) {

        return list;

    private T convertInstanceOfObject(Object o) {
        try {
            return (T) o;
        } catch (ClassCastException e) {
            return null;

and then in terms of how it ties in with the database, I have the following:

// connect to database (autocloses)
try (DataConnection conn = ds1.getConnection()) {

    // fetch rows
    List<Map<String, Object>> rows = conn.nativeSelect("SELECT * FROM products");

    // map rows to class
    ObjectMapper<Product> objectMapper = new ObjectMapper<>(Product.class);
    List<Product> products =;

    // display the rows

    // display it as products
    for (Product prod : products) {

} catch (Exception e) {

How to stop java process gracefully?

Similar Question Here

Finalizers in Java are bad. They add a lot of overhead to garbage collection. Avoid them whenever possible.

The shutdownHook will only get called when the VM is shutting down. I think it very well may do what you want.

Apply a function to every row of a matrix or a data frame

You simply use the apply() function:

R> M <- matrix(1:6, nrow=3, byrow=TRUE)
R> M
     [,1] [,2]
[1,]    1    2
[2,]    3    4
[3,]    5    6
R> apply(M, 1, function(x) 2*x[1]+x[2])
[1]  4 10 16

This takes a matrix and applies a (silly) function to each row. You pass extra arguments to the function as fourth, fifth, ... arguments to apply().

Can I do a max(count(*)) in SQL?

Thanks to the last answer

SELECT yr, COUNT(title)
FROM actor
JOIN casting ON = casting.actorid
JOIN movie ON casting.movieid =
WHERE name = 'John Travolta'
  (SELECT COUNT(title)
   FROM actor
   JOIN casting ON = casting.actorid
   JOIN movie ON casting.movieid =
   WHERE name = 'John Travolta'
   GROUP BY yr)

I had the same problem: I needed to know just the records which their count match the maximus count (it could be one or several records).

I have to learn more about "ALL clause", and this is exactly the kind of simple solution that I was looking for.

Tainted canvases may not be exported

I resolved the problem using useCORS: true option

 html2canvas(document.getElementsByClassName("droppable-area")[0], { useCORS:true}).then(function (canvas){
        var imgBase64 = canvas.toDataURL();
        // console.log("imgBase64:", imgBase64);
        var imgURL = "data:image/" + imgBase64;
        var triggerDownload = $("<a>").attr("href", imgURL).attr("download", "layout_"+new Date().getTime()+".jpeg").appendTo("body");

How do you add swap to an EC2 instance?

You can use the following script to add swap on Amazon Linux.

Download the script using wget:

wget -O

Then run the script with the following format:

sh 2G

For a complete tutorial you can visit:

Default session timeout for Apache Tomcat applications

Open $CATALINA_BASE/conf/web.xml and find this

<!-- ==================== Default Session Configuration ================= -->
<!-- You can set the default session timeout (in minutes) for all newly   -->
<!-- created sessions by modifying the value below.                       -->


all webapps implicitly inherit from this default web descriptor. You can override session-config as well as other settings defined there in your web.xml.

This is actually from my Tomcat 7 (Windows) but I think 5.5 conf is not very different

How to use a parameter in ExecStart command line?

Although systemd indeed does not provide way to pass command-line arguments for unit files, there are possibilities to write instances:

For example: /lib/systemd/system/[email protected] looks something like this:

Description=Serial Getty on %I
After=dev-%i.device systemd-user-sessions.service

ExecStart=-/sbin/agetty -s %I 115200,38400,9600

So, you may start it like:

$ systemctl start [email protected]
$ systemctl start [email protected]

For systemd it will different instances:

$ systemctl status [email protected]
[email protected] - Getty on ttyUSB0
      Loaded: loaded (/lib/systemd/system/[email protected]; static)
      Active: active (running) since Mon, 26 Sep 2011 04:20:44 +0200; 2s ago
    Main PID: 5443 (agetty)
      CGroup: name=systemd:/system/[email protected]/ttyUSB0
          + 5443 /sbin/agetty -s ttyUSB0 115200,38400,9600

It also mean great possibility enable and disable it separately.

Off course it lack much power of command line parsing, but in common way it is used as some sort of config files selection. For example you may look at Fedora [email protected]:[email protected]

How to use ConcurrentLinkedQueue?

No, the methods don't need to be synchronized, and you don't need to define any methods; they are already in ConcurrentLinkedQueue, just use them. ConcurrentLinkedQueue does all the locking and other operations you need internally; your producer(s) adds data into the queue, and your consumers poll for it.

First, create your queue:

Queue<YourObject> queue = new ConcurrentLinkedQueue<YourObject>();

Now, wherever you are creating your producer/consumer objects, pass in the queue so they have somewhere to put their objects (you could use a setter for this, instead, but I prefer to do this kind of thing in a constructor):

YourProducer producer = new YourProducer(queue);


YourConsumer consumer = new YourConsumer(queue);

and add stuff to it in your producer:


and take stuff out in your consumer (if the queue is empty, poll() will return null, so check it):

YourObject myObject = queue.poll();

For more info see the Javadoc


If you need to block waiting for the queue to not be empty, you probably want to use a LinkedBlockingQueue, and use the take() method. However, LinkedBlockingQueue has a maximum capacity (defaults to Integer.MAX_VALUE, which is over two billion) and thus may or may not be appropriate depending on your circumstances.

If you only have one thread putting stuff into the queue, and another thread taking stuff out of the queue, ConcurrentLinkedQueue is probably overkill. It's more for when you may have hundreds or even thousands of threads accessing the queue at the same time. Your needs will probably be met by using:

Queue<YourObject> queue = Collections.synchronizedList(new LinkedList<YourObject>());

A plus of this is that it locks on the instance (queue), so you can synchronize on queue to ensure atomicity of composite operations (as explained by Jared). You CANNOT do this with a ConcurrentLinkedQueue, as all operations are done WITHOUT locking on the instance (using java.util.concurrent.atomic variables). You will NOT need to do this if you want to block while the queue is empty, because poll() will simply return null while the queue is empty, and poll() is atomic. Check to see if poll() returns null. If it does, wait(), then try again. No need to lock.


Honestly, I'd just use a LinkedBlockingQueue. It is still overkill for your application, but odds are it will work fine. If it isn't performant enough (PROFILE!), you can always try something else, and it means you don't have to deal with ANY synchronized stuff:

BlockingQueue<YourObject> queue = new LinkedBlockingQueue<YourObject>();

queue.put(myObject); // Blocks until queue isn't full.

YourObject myObject = queue.take(); // Blocks until queue isn't empty.

Everything else is the same. Put probably won't block, because you aren't likely to put two billion objects into the queue.

Full screen background image in an activity

In lines with the answer of NoToast, you would need to have multiple versions of "your_image" in your res/drawable-ldpi,mdpi, hdpi, x-hdpi (for xtra large screens), remove match_parent and keep android: adjustViewBounds="true"

Text inset for UITextField?

To throw in another solution that has no need for subclassing:

UITextField *txtField = [UITextField new];
txtField.borderStyle = UITextBorderStyleRoundedRect;

// grab BG layer
CALayer *bgLayer = txtField.layer.sublayers.lastObject;
bgLayer.opacity = 0.f;

// add new bg view
UIView *bgView = [UIView new];
bgView.backgroundColor = [UIColor whiteColor];
bgView.autoresizingMask = UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth;
bgView.userInteractionEnabled = NO;

[txtField addSubview: bgView];
[txtField sendSubviewToBack: bgView];

Original UITextField Fixed UITextField

Tested with iOS 7 and iOS 8. Both working. Still there might be the chance of Apple modifying the UITextField's layer hierarchy screwing up things badly.

Access a function variable outside the function without using "global"

I've experienced the same problem. One of the responds to your question led me to the following idea (which worked eventually). I use Python 3.7.

    # just an example 
    def func(): # define a function
       func.y = 4 # here y is a local variable, which I want to access; func.y defines 
                  # a method for my example function which will allow me to access 
                  # function's local variable y
       x = func.y + 8 # this is the main task for the function: what it should do
       return x

    func() # now I'm calling the function
    a = func.y # I put it's local variable into my new variable
    print(a) # and print my new variable

Then I launch this program in Windows PowerShell and get the answer 4. Conclusion: to be able to access a local function's variable one might add the name of the function and a dot before the name of the local variable (and then, of course, use this construction for calling the variable both in the function's body and outside of it). I hope this will help.

Use of 'prototype' vs. 'this' in JavaScript?

What's the difference? => A lot.

I think, the this version is used to enable encapsulation, i.e. data hiding. It helps to manipulate private variables.

Let us look at the following example:

var AdultPerson = function() {

  var age;

  this.setAge = function(val) {
    // some housekeeping
    age = val >= 18 && val;

  this.getAge = function() {
    return age;

  this.isValid = function() {
    return !!age;

Now, the prototype structure can be applied as following:

Different adults have different ages, but all of the adults get the same rights.
So, we add it using prototype, rather than this.

AdultPerson.prototype.getRights = function() {
  // Should be valid
  return this.isValid() && ['Booze', 'Drive'];

Lets look at the implementation now.

var p1 = new AdultPerson;
p1.setAge(12); // ( age = false )
console.log(p1.getRights()); // false ( Kid alert! )
p1.setAge(19); // ( age = 19 )
console.log(p1.getRights()); // ['Booze', 'Drive'] ( Welcome AdultPerson )

var p2 = new AdultPerson;
console.log(p2.getRights()); // The same getRights() method, *** not a new copy of it ***

Hope this helps.

pandas how to check dtype for all columns in a dataframe?

The singular form dtype is used to check the data type for a single column. And the plural form dtypes is for data frame which returns data types for all columns. Essentially:

For a single column:


For all columns:



import pandas as pd
df = pd.DataFrame({'A': [1,2,3], 'B': [True, False, False], 'C': ['a', 'b', 'c']})

# dtype('int64')
# dtype('bool')
# dtype('O')

#A     int64
#B      bool
#C    object
#dtype: object

How can I add a new column and data to a datatable that already contains data?

Here is an alternate solution to reduce For/ForEach looping, this would reduce looping time and updates quickly :)

 dt.Columns.Add("MyRow", typeof(System.Int32));
 dt.Columns["MyRow"].Expression = "'0'";

How to reload .bashrc settings without logging out and back in again?

I noticed that pure exec bash command will preserve the environment variables, so you need to use exec -c bash to run bash in an empty environment.

For example, you login a bash, and export A=1, if you exec bash, the A == 1.

If you exec -cl bash, A is empty.

I think this is the best way to do your job.

python uninstall

If you still have files that are supposed to be deleted after re-installing a package, make sure the folder build is also deleted. Therefore, assuming that pkg is the package you want to delete:

rm -r $(python3 -c "import pkg; print(pkg.__path__[0] + '*' )") 
rm -rf build

Obove work out for python3 and delete the package and its *.egg-info file

A html space is showing as %2520 instead of %20

A bit of explaining as to what that %2520 is :

The common space character is encoded as %20 as you noted yourself. The % character is encoded as %25.

The way you get %2520 is when your url already has a %20 in it, and gets urlencoded again, which transforms the %20 to %2520.

Are you (or any framework you might be using) double encoding characters?

Edit: Expanding a bit on this, especially for LOCAL links. Assuming you want to link to the resource C:\my path\my file.html:

  • if you provide a local file path only, the browser is expected to encode and protect all characters given (in the above, you should give it with spaces as shown, since % is a valid filename character and as such it will be encoded) when converting to a proper URL (see next point).
  • if you provide a URL with the file:// protocol, you are basically stating that you have taken all precautions and encoded what needs encoding, the rest should be treated as special characters. In the above example, you should thus provide file:///c:/my%20path/my%20file.html. Aside from fixing slashes, clients should not encode characters here.


  • Slash direction - forward slashes / are used in URLs, reverse slashes \ in Windows paths, but most clients will work with both by converting them to the proper forward slash.
  • In addition, there are 3 slashes after the protocol name, since you are silently referring to the current machine instead of a remote host ( the full unabbreviated path would be file://localhost/c:/my%20path/my%file.html ), but again most clients will work without the host part (ie two slashes only) by assuming you mean the local machine and adding the third slash.

How to increase heap size of an android application?

Increasing Java Heap unfairly eats deficit mobile resurces. Sometimes it is sufficient to just wait for garbage collector and then resume your operations after heap space is reduced. Use this static method then.

How do I include a JavaScript script file in Angular and call a function from that script?

In order to include a global library, eg jquery.js file in the scripts array from angular-cli.json (angular.json when using angular 6+):

"scripts": [

After this, restart ng serve if it is already started.

How do I install the babel-polyfill library?

Like Babel says in the docs, for Babel > 7.4.0 the module @babel/polyfill is deprecated, so it's recommended to use directly core-js and regenerator-runtime libraries that before were included in @babel/polyfill.

So this worked for me:

npm install --save [email protected]
npm install regenerator-runtime

then add to the very top of your initial js file:

import 'core-js/stable';
import 'regenerator-runtime/runtime';

How can I generate a list of consecutive numbers?

Note :- Certainly in python-3x you need to use Range function It works to generate numbers on demand, standard method to use Range function to make a list of consecutive numbers is

print (x)
#Output_is_ [0,1,2,3,4,5,6,7,8,9]

Also if you want to make an function to generate a list of consecutive numbers by using Range function watch this code !

def  consecutive_numbers(n) :
    list=[i for i in range(n)]
    return (list)

Good Luck!

How to convert datetime format to date format in crystal report using C#?

In case the formatting needs to be done on Crystal Report side.

Simple way.

Crystal Report Design Window->Right click on the date field->format Field->Customize the date format per your need.

Works effectively.

How to change a TextView's style at runtime

Like Jonathan suggested, using textView.setTextTypeface works, I just used it in an app a few seconds ago.

textView.setTypeface(null, Typeface.BOLD); // Typeface.NORMAL, Typeface.ITALIC etc.

How to upload file using Selenium WebDriver in Java

I have tried to use the above robot there is a need to add a delay :( also you cannot debug or do something else because you lose the focus :(

//open upload window;

//put path to your image in a clipboard
StringSelection ss = new StringSelection(file.getAbsoluteFile());
Toolkit.getDefaultToolkit().getSystemClipboard().setContents(ss, null);

//imitate mouse events like ENTER, CTRL+C, CTRL+V
Robot robot = new Robot();

Setting a minimum/maximum character count for any character using a regular expression

If you want to set Min 1 count and no Max length,


How to search for occurrences of more than one space between words in a line

This regex selects all spaces, you can use this and replace it with a single space


example in python

result = re.sub('\s+',' ', data))

Python, Unicode, and the Windows console

Like Giampaolo Rodolà's answer, but even more dirty: I really, really intend to spend a long time (soon) understanding the whole subject of encodings and how they apply to Windoze consoles,

For the moment I just wanted sthg which would mean my program would NOT CRASH, and which I understood ... and also which didn't involve importing too many exotic modules (in particular I'm using Jython, so half the time a Python module turns out not in fact to be available).

def pr(s):
    except UnicodeEncodeError:
        for c in s:
                print( c, end='')
            except UnicodeEncodeError:
                print( '?', end='')

NB "pr" is shorter to type than "print" (and quite a bit shorter to type than "safeprint")...!

PowerShell The term is not recognized as cmdlet function script file or operable program

Yet another way this error message can occur...

If PowerShell is open in a directory other than the target file, e.g.:

If someScript.ps1 is located here: C:\SlowLearner\some_missing_path\someScript.ps1, then C:\SlowLearner>. ./someScript.ps1 wont work.

In that case, navigate to the path: cd some_missing_path then this would work:

C:\SlowLearner\some_missing_path>. ./someScript.ps1

CSS3 gradient background set on body doesn't stretch but instead repeats?

Regarding a previous answer, setting html and body to height: 100% doesn't seem to work if the content needs to scroll. Adding fixed to the background seems to fix that - no need for height: 100%;


body {_x000D_
  background: -webkit-gradient(linear, left top, left bottom, from(#fff), to(#cbccc8)) fixed;_x000D_

How do I count unique items in field in Access query?

Try this

SELECT Count(*) AS N

Read this for more info.

select2 onchange event only works once

Apparently the change event is not fired if a selection already exists when using data. I ended up updating the data manually on select to resolve the problem.

$("#search_code").on("select2-selecting", function(e) {

I know this is pretty late but hopefully this answer will save others time.

How to check the function's return value if true or false

you're comparing the result against a string ('false') not the built-in negative constant (false)

just use

if(ValidateForm() == false) {

or better yet

if(!ValidateForm()) {

also why are you calling validateForm twice?

Using Oracle to_date function for date string with milliseconds

An Oracle DATE does not store times with more precision than a second. You cannot store millisecond precision data in a DATE column.

Your two options are to either truncate the string of the milliseconds before converting it into a DATE, i.e.

to_date( substr('23.12.2011 13:01:001', 1, 19), 'DD.MM.YYYY HH24:MI:SS' )

or to convert the string into a TIMESTAMP that does support millisecond precision

to_timestamp( '23.12.2011 13:01:001', 'DD.MM.YYYY HH24:MI:SSFF3' )

Permanently adding a file path to sys.path in Python

There are a few ways. One of the simplest is to create a my-paths.pth file (as described here). This is just a file with the extension .pth that you put into your system site-packages directory. On each line of the file you put one directory name, so you can put a line in there with /path/to/the/ and it will add that directory to the path.

You could also use the PYTHONPATH environment variable, which is like the system PATH variable but contains directories that will be added to sys.path. See the documentation.

Note that no matter what you do, sys.path contains directories not files. You can't "add a file to sys.path". You always add its directory and then you can import the file.

Trigger standard HTML5 validation (form) without using submit button?

form.submit() doesn't work cause the HTML5 validation is performed before the form submition. When you click on a submit button, the HTML5 validation is trigerred and then the form is submited if validation was successfull.

What is the ideal data type to use when storing latitude / longitude in a MySQL database?

Depends on the precision that you require.

Datatype           Bytes       resolution
------------------ -----  --------------------------------
Deg*100 (SMALLINT)     4  1570 m    1.0 mi  Cities
DECIMAL(4,2)/(5,2)     5  1570 m    1.0 mi  Cities
SMALLINT scaled        4   682 m    0.4 mi  Cities
Deg*10000 (MEDIUMINT)  6    16 m     52 ft  Houses/Businesses
DECIMAL(6,4)/(7,4)     7    16 m     52 ft  Houses/Businesses
MEDIUMINT scaled       6   2.7 m    8.8 ft
FLOAT                  8   1.7 m    5.6 ft
DECIMAL(8,6)/(9,6)     9    16cm    1/2 ft  Friends in a mall
Deg*10000000 (INT)     8    16mm    5/8 in  Marbles
DOUBLE                16   3.5nm     ...    Fleas on a dog


To summarise:

  • The most precise available option is DOUBLE.
  • The most common seen type used is DECIMAL(8,6)/(9,6).

As of MySQL 5.7, consider using Spatial Data Types (SDT), specifically POINT for storing a single coordinate. Prior to 5.7, SDT does not support indexes (with exception of 5.6 when table type is MyISAM).


  • When using POINT class, the order of the arguments for storing coordinates must be POINT(latitude, longitude).
  • There is a special syntax for creating a spatial index.
  • The biggest benefit of using SDT is that you have access to Spatial Analyses Functions, e.g. calculating distance between two points (ST_Distance) and determining whether one point is contained within another area (ST_Contains).

How to get the body's content of an iframe in Javascript?

Chalkey is correct, you need to use the src attribute to specify the page to be contained in the iframe. Providing you do this, and the document in the iframe is in the same domain as the parent document, you can use this:

var e = document.getElementById("id_description_iframe");
if(e != null) {

Obviously you can then do something useful with the contents instead of just putting them in an alert.

Maven plugin not using Eclipse's proxy settings

Eclipse by default does not know about your external Maven installation and uses the embedded one. Therefore in order for Eclipse to use your global settings you need to set it in menu Settings ? Maven ? Installations.

Google Maps API v2: How to make markers clickable?

I added a mMap.setOnMarkerClickListener(this); in the onMapReady(GoogleMap googleMap) method. So every time you click a marker it displays the text name in the toast method.

public class DemoMapActivity extends AppCompatActivity implements NavigationView.OnNavigationItemSelectedListener,OnMapReadyCallback, GoogleMap.OnMarkerClickListener {

private GoogleMap mMap;

protected void onCreate(Bundle savedInstanceState) {
    Toolbar toolbar = findViewById(;
    SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager().findFragmentById(;

public void onMapReady(GoogleMap googleMap) {
    mMap = googleMap;
    double lat=0.34924212701428;
    double lng=32.616554024713;
    String venue = "Capital Shoppers City";
    LatLng location = new LatLng(lat, lng);
    mMap.addMarker(new MarkerOptions().position(location).title(venue)).setTag(0);
    CameraUpdate cameraUpdate = CameraUpdateFactory.newLatLng(location);
    CameraUpdate zoom = CameraUpdateFactory.zoomTo(16);

public boolean onMarkerClick(final Marker marker) {
    // Retrieve the data from the marker.
    Integer clickCount = (Integer) marker.getTag();

    // Check if a click count was set, then display the click count.
    if (clickCount != null) {
        clickCount = clickCount + 1;
                       marker.getTitle() +
                       " has been clicked ",
    // Return false to indicate that we have not consumed the event and that we wish
    // for the default behavior to occur (which is for the camera to move such that the
    // marker is centered and for the marker's info window to open, if it has one).
    return false;


You can check this link for reference Markers

What's is the difference between train, validation and test set, in neural networks?

Cross-validation set is used for model selection, for example, select the polynomial model with the least amount of errors for a given parameter set. The test set is then used to report the generalization error on the selected model. From here:

Prevent redirect after form is submitted

You can use as below


If this method is called, the default action of the event will not be triggered.

Also if I may suggest read this: .prop() vs .attr()

I hope it will help you,

code example:

    //do what you want

CSS/Javascript to force html table row on a single line

For those further interested:

Existing Dynamic Table Cells: ## Long text with NO SPACES i.e. email addresses ##

It appears a full replication of the MS (and others) use of text-overflow:ellipsis cannot be duped in FireFox so far as adding the internally appended to clipped text is concerned; especially without javascript which is often user switched off these days.

All ideas I have found to help me have failed to address dynamic resizing and long text without spaces.

However, I had a need for clipping in a dynamic width table in one of my progs admin windows. So with a little fiddling an acceptable all browser answer can be hacked from the supplied samples at “MSDN”.


<table width="20%" border="1" STYLE="position: absolute; top: 100;">

<td width="100%"><DIV STYLE="position: relative; height: 14px; top: 0px; width:100%;">
<DIV STYLE="position: absolute; left: 0px; top: 0px; color: black; width: 100%; height: 14px;
    font: 12px Verdana, Arial, Geneva, sans-serif; overflow: hidden; text-overflow:ellipsis;">
<NOBR>fasfasfasfasfsfsffsdafffsafsfsfsfsfasfsfsfsafsfsfsfWe hold these truths to be self-evident, that all people are created equal.</NOBR></DIV>


Only small shortcoming is Firefox users don’t see the “…” bit; which is summink I don’t really mind at this stage.

Future FF should, hopefully, resolve gracefully if implementing this very important useful option. So now I don’t need to rewrite using less favorable futuristic non tabled content either (don’t argue; there’s plenty of broken web sites around ’cause of it these days).

Thanks to:

Hope it helps some bod.

Find all matches in workbook using Excel VBA

You may use the Range.Find method:

This will get you the first cell which contains the search string. By repeating this with setting the "After" argument to the next cell you will get all other occurrences until you are back at the first occurrence.

This will likely be much faster.

How to play ringtone/alarm sound in Android

For the future googlers: use RingtoneManager.getActualDefaultRingtoneUri() instead of RingtoneManager.getDefaultUri(). According to its name, it would return the actual uri, so you can freely use it. From documentation of getActualDefaultRingtoneUri():

Gets the current default sound's Uri. This will give the actual sound Uri, instead of using this, most clients can use DEFAULT_RINGTONE_URI.

Meanwhile getDefaultUri() says this:

Returns the Uri for the default ringtone of a particular type. Rather than returning the actual ringtone's sound Uri, this will return the symbolic Uri which will resolved to the actual sound when played.

Execute php file from another php

This came across while working on a project on linux platform.

exec('wget http://<url to the php script>)

This runs as if you run the script from browser.

Hope this helps!!

Can't access RabbitMQ web management interface after fresh install

Something that just happened to me and caused me some headaches:

I have set up a new Linux RabbitMQ server and used a shell script to set up my own custom users (not guest!).

The script had several of those "code" blocks:

rabbitmqctl add_user test test
rabbitmqctl set_user_tags test administrator
rabbitmqctl set_permissions -p / test ".*" ".*" ".*"

Very similar to the one in Gabriele's answer, so I take his code and don't need to redact passwords.

Still I was not able to log in in the management console. Then I noticed that I had created the setup script in Windows (CR+LF line ending) and converted the file to Linux (LF only), then reran the setup script on my Linux server.

... and was still not able to log in, because it took another 15 minutes until I realized that calling add_user over and over again would not fix the broken passwords (which probably ended with a CR character). I had to call change_password for every user to fix my earlier mistake:

rabbitmqctl change_password test test

(Another solution would have been to delete all users and then call the script again)

How to set time zone in codeigniter?

Add this line to autoload.php in the application folder:

$autoload['time_zone'] = date_default_timezone_set('Asia/Kolkata');

Iterate through a C array

You can store the size somewhere, or you can have a struct with a special value set that you use as a sentinel, the same way that '\0' indicates the end of a string.

How to ensure a <select> form field is submitted when it is disabled?

Or use some JavaScript to change the name of the select and set it to disabled. This way the select is still submitted, but using a name you aren't checking.

Print array without brackets and commas

Basically, don't use ArrayList.toString() - build the string up for yourself. For example:

StringBuilder builder = new StringBuilder();
for (String value : publicArray) {
String text = builder.toString();

(Personally I wouldn't call the variable publicArray when it's not actually an array, by the way.)

chart.js load totally new data

With Chart.js V2.0 you can to do the following: = some_new_data;

IDEA: javac: source release 1.7 requires target release 1.7

You need to change Java compiler version in in build config.

enter image description here

How do I create a comma-separated list from an array in PHP?

I prefer to use an IF statement in the FOR loop that checks to make sure the current iteration isn't the last value in the array. If not, add a comma

$fruit = array("apple", "banana", "pear", "grape");

for($i = 0; $i < count($fruit); $i++){
    echo "$fruit[$i]";
    if($i < (count($fruit) -1)){
      echo ", ";

Flexbox not working in Internet Explorer 11

According to Flexbugs:

In IE 10-11, min-height declarations on flex containers work to size the containers themselves, but their flex item children do not seem to know the size of their parents. They act as if no height has been set at all.

Here are a couple of workarounds:

1. Always fill the viewport + scrollable <aside> and <section>:

html {
  height: 100%;

body {
  display: flex;
  flex-direction: column;
  height: 100%;
  margin: 0;

footer {
  background: #7092bf;

main {
  flex: 1;
  display: flex;

aside, section {
  overflow: auto;

aside {
  flex: 0 0 150px;
  background: #3e48cc;

section {
  flex: 1;
  background: #9ad9ea;



2. Fill the viewport initially + normal page scroll with more content:

html {
  height: 100%;

body {
  display: flex;
  flex-direction: column;
  height: 100%;
  margin: 0;

footer {
  background: #7092bf;

main {
  flex: 1 0 auto;
  display: flex;

aside {
  flex: 0 0 150px;
  background: #3e48cc;

section {
  flex: 1;
  background: #9ad9ea;



How do I get the directory of the PowerShell script I execute?

PowerShell 3 has the $PSScriptRoot automatic variable:

Contains the directory from which a script is being run.

In Windows PowerShell 2.0, this variable is valid only in script modules (.psm1). Beginning in Windows PowerShell 3.0, it is valid in all scripts.

Don't be fooled by the poor wording. PSScriptRoot is the directory of the current file.

In PowerShell 2, you can calculate the value of $PSScriptRoot yourself:

# PowerShell v2
$PSScriptRoot = Split-Path -Parent -Path $MyInvocation.MyCommand.Definition

Easiest way to parse a comma delimited string to some kind of object I can loop through to access the individual values?

there are gotchas with this - but ultimately the simplest way will be to use

string s = [yourlongstring];
string[] values = s.Split(',');

If the number of commas and entries isn't important, and you want to get rid of 'empty' values then you can use

string[] values = s.Split(",".ToCharArray(), StringSplitOptions.RemoveEmptyEntries);

One thing, though - this will keep any whitespace before and after your strings. You could use a bit of Linq magic to solve that:

string[] values = s.Split(',').Select(sValue => sValue.Trim()).ToArray();

That's if you're using .Net 3.5 and you have the using System.Linq declaration at the top of your source file.

Python `if x is not None` or `if not x is None`?

The answer is simpler than people are making it.

There's no technical advantage either way, and "x is not y" is what everybody else uses, which makes it the clear winner. It doesn't matter that it "looks more like English" or not; everyone uses it, which means every user of Python--even Chinese users, whose language Python looks nothing like--will understand it at a glance, where the slightly less common syntax will take a couple extra brain cycles to parse.

Don't be different just for the sake of being different, at least in this field.

Create two threads, one display odd & other even numbers

Below is the code which uses lock on a shared object which has the number to be printed. It guarantees the sequence also unlike the above solution.

public class MultiThreadPrintNumber {
  int i = 1;

  public synchronized void printNumber(String threadNm) throws InterruptedException{

        if(i%2 == 1){
          System.out.println(Thread.currentThread().getName()+"--"+ i++);
        } else {
      } else if(threadNm.equals("t2")){
        if(i%2 == 0){
          System.out.println(Thread.currentThread().getName()+"--"+ i++);
        } else {


  public static void main(String[] args) {
    final MultiThreadPrintNumber obj = new MultiThreadPrintNumber();
    Thread t1 = new Thread(new Runnable() {

      public void run() {
        try {
          while(obj.i <= 10){

        } catch (InterruptedException e) {
          // TODO Auto-generated catch block
        System.out.println("done t1");
    Thread t2 = new Thread(new Runnable() {

      public void run() {
        try {
          while(obj.i <=10){
        } catch (InterruptedException e) {
          // TODO Auto-generated catch block
        System.out.println("done t2");


The output will look like: t1--1 t2--2 t1--3 t2--4 t1--5 t2--6 t1--7 t2--8 t1--9 t2--10 done t2 done t1

How to convert float number to Binary?

Keep multiplying the number after decimal by 2 till it becomes 1.0:

0.25*2 = 0.50
0.50*2 = 1.00

and the result is in reverse order being .01

Socket.IO - how do I get a list of connected sockets/clients?

I think we can access the socket object from the server, and you can assign the nickname, and point its socket id,

    io.sockets.sockets['nickname'] =;
    client.on("chat", function(data) {      
        var sock_id = io.sockets.sockets['nickname']
        io.sockets.sockets[sock_id].emit("private", "message");

On disconnect please remove the nickname from io.sockets.sockets.

How is VIP swapping + CNAMEs better than IP swapping + A records?

A VIP swap is an internal change to Azure's routers/load balancers, not an external DNS change. They're just routing traffic to go from one internal [set of] server[s] to another instead. Therefore the DNS info for doesn't change at all. Therefore the change for people accessing via the IP bound to (and CNAME'd by you) will see the change as soon as the VIP swap is complete.

What is the correct way to write HTML using Javascript?

  1. DOM methods, as outlined by Tom.

  2. innerHTML, as mentioned by iHunger.

DOM methods are highly preferable to strings for setting attributes and content. If you ever find yourself writing innerHTML= '<a href="'+path+'">'+text+'</a>' you're actually creating new cross-site-scripting security holes on the client side, which is a bit sad if you've spent any time securing your server-side.

DOM methods are traditionally described as ‘slow’ compared to innerHTML. But this isn't really the whole story. What is slow is inserting a lot of child nodes:

 for (var i= 0; i<1000; i++)
     div.parentNode.insertBefore(document.createElement('div'), div);

This translates to a load of work for the DOM finding the right place in its nodelist to insert the element, moving the other child nodes up, inserting the new node, updating the pointers, and so on.

Setting an existing attribute's value, or a text node's data, on the other hand, is very fast; you just change a string pointer and that's it. This is going to be much faster than serialising the parent with innerHTML, changing it, and parsing it back in (and won't lose your unserialisable data like event handlers, JS references and form values).

There are techniques to do DOM manipulations without so much slow childNodes walking. In particular, be aware of the possibilities of cloneNode, and using DocumentFragment. But sometimes innerHTML really is quicker. You can still get the best of both worlds by using innerHTML to write your basic structure with placeholders for attribute values and text content, which you then fill in afterwards using DOM. This saves you having to write your own escapehtml() function to get around the escaping/security problems mentioned above.

Platform.runLater and Task in JavaFX

One reason to use an explicite Platform.runLater() could be that you bound a property in the ui to a service (result) property. So if you update the bound service property, you have to do this via runLater():

In UI thread also known as the JavaFX Application thread:


in Service implementation (background worker):

Platform.runLater(() -> result.add("Element " + finalI));

What primitive data type is time_t?

Unfortunately, it's not completely portable. It's usually integral, but it can be any "integer or real-floating type".

Exclude Blank and NA in R

Don't know exactly what kind of dataset you have, so I provide general answer.

x <- c(1,2,NA,3,4,5)
y <- c(1,2,3,NA,6,8) <- data.frame(x, y)
   x  y
1  1  1
2  2  2
3 NA  3
4  3 NA
5  4  6
6  5  8
# Exclude rows with NA values[complete.cases(,]
  x y
1 1 1
2 2 2
5 4 6
6 5 8

ReCaptcha API v2 Styling

With the integration of the invisible reCAPTCHA you can do the following:

To enable the Invisible reCAPTCHA, rather than put the parameters in a div, you can add them directly to an html button.

a. data-callback=””. This works just like the checkbox captcha, but is required for invisible.

b. data-badge: This allows you to reposition the reCAPTCHA badge (i.e. logo and ‘protected by reCAPTCHA’ text) . Valid options as ‘bottomright’ (the default), ‘bottomleft’ or ‘inline’ which will put the badge directly above the button. If you make the badge inline, you can control the CSS of the badge directly.

Why doesn't indexOf work on an array IE8?

You can use this to replace the function if it doesn't exist:

if (!Array.prototype.indexOf) {
    Array.prototype.indexOf = function(elt /*, from*/) {
        var len = this.length >>> 0;

        var from = Number(arguments[1]) || 0;
        from = (from < 0) ? Math.ceil(from) : Math.floor(from);
        if (from < 0)
            from += len;

        for (; from < len; from++) {
            if (from in this && this[from] === elt)
                return from;
        return -1;

How do I clear the std::queue efficiently?

Assuming your m_Queue contains integers:


Otherwise, if it contains e.g. pointers to Job objects, then:


This way you swap an empty queue with your m_Queue, thus m_Queue becomes empty.

How To Inject AuthenticationManager using Java Configuration in a Custom Filter

Override method authenticationManagerBean in WebSecurityConfigurerAdapter to expose the AuthenticationManager built using configure(AuthenticationManagerBuilder) as a Spring bean:

For example:

   public AuthenticationManager authenticationManagerBean() throws Exception {
       return super.authenticationManagerBean();

How to delete and recreate from scratch an existing EF Code First database

There re many ways to drop a database or update existing database, simply you can switched to previous migrations.

dotnet ef database update previousMigraionName    

But some databases have limitations like not allow to modify after create relationships, means you have not allow privileges to drop columns from ef core database providers but most of time in ef core drop database is you can drop DB using drop command and then you use previous migration again.

dotnet ef database drop
PMC command 
PM> drop-database

OR you can do manually deleting database and do a migration.

How to convert a byte array to its numeric value (Java)?

Complete java converter code for all primitive types to/from arrays

git pull remote branch cannot find remote ref

I had this issue when after rebooted and the last copy of VSCode reopened. The above fix did not work, but when I closed and reopened VSCode via explorer it worked. Here are the steps I did:

//received fatal error_x000D_
git remote remove origin_x000D_
git init_x000D_
git remote add origin git@github:<yoursite>/<your project>.git_x000D_
// still received an err _x000D_
//restarted VSCode and folder via IE _x000D_
//updated one char and resaved the index.html  _x000D_
git add ._x000D_
git commit -m "blah"_x000D_
git push origin master

JQuery get all elements by class name

Maybe not as clean or efficient as the already posted solutions, but how about the .each() function? E.g:

var mvar = "";
$(".mbox").each(function() {
    mvar += $(this).html();

Like Operator in Entity Framework?

Update: In EF 6.2 there is a like operator

Where(obj => DbFunctions.Like(obj.Column , "%expression%")

Accessing a property in a parent Component

There are different way:

export class Profile implements OnInit {
constructor(@Host() parent: App) {
  parent.userStatus ...
  • data-binding
export class Profile implements OnInit {
  @Input() userStatus:UserStatus;

<profile [userStatus]="userStatus">

JSONDecodeError: Expecting value: line 1 column 1 (char 0)

I was having the same problem with requests (the python library). It happened to be the accept-encoding header.

It was set this way: 'accept-encoding': 'gzip, deflate, br'

I simply removed it from the request and stopped getting the error.

Replacing NULL and empty string within Select statement

For an example data in your table such as combinations of

'', null and as well as actual value than if you want to only actual value and replace to '' and null value by # symbol than execute this query

SELECT Column_Name = (CASE WHEN (Column_Name IS NULL OR Column_Name = '') THEN '#' ELSE Column_Name END) FROM Table_Name

and another way you can use it but this is little bit lengthy and instead of this you can also use IsNull function but here only i am mentioning IIF function

SELECT IIF(Column_Name IS NULL, '#', Column_Name) FROM Table_Name  
SELECT IIF(Column_Name  = '', '#', Column_Name) FROM Table_Name  
-- and syntax of this query
SELECT IIF(Column_Name IS NULL, 'True Value', 'False Value') FROM Table_Name

How do I get a YouTube video thumbnail from the YouTube API?

public const string tubeThumb = "[id]/hqdefault.jpg";
vid.Thumbnail = tubeThumb.Replace("[id]", vid.VideoID);

C++ How do I convert a std::chrono::time_point to long and back

I would also note there are two ways to get the number of ms in the time point. I'm not sure which one is better, I've benchmarked them and they both have the same performance, so I guess it's a matter of preference. Perhaps Howard could chime in:

auto now = system_clock::now();

//Cast the time point to ms, then get its duration, then get the duration's count.
auto ms = time_point_cast<milliseconds>(now).time_since_epoch().count();

//Get the time point's duration, then cast to ms, then get its count.
auto ms = duration_cast<milliseconds>(tpBid.time_since_epoch()).count();

The first one reads more clearly in my mind going from left to right.

Combination of async function + await + setTimeout

The following code works in Chrome and Firefox and maybe other browsers.

function timeout(ms) {
    return new Promise(resolve => setTimeout(resolve, ms));
async function sleep(fn, ...args) {
    await timeout(3000);
    return fn(...args);

But in Internet Explorer I get a Syntax Error for the "(resolve **=>** setTimeout..."

Detect change to selected date with bootstrap-datepicker

$(function() {_x000D_
    defaultDate: new Date()_x000D_
    $('#newDateSpan').html("New Date: " +'lll'));_x000D_
    $('#oldDateSpan').html("Old Date: " + event.oldDate.format('lll'));_x000D_
<link href="" rel="stylesheet"/>_x000D_
<link href="" rel="stylesheet"/>_x000D_
<script src=""></script>_x000D_
<script src=""></script>_x000D_
<script src=""></script>_x000D_
<script src=""></script>_x000D_
<div class="container">_x000D_
  <div class="col-xs-12">_x000D_
    <input name="datetimepicker" />_x000D_
    <p><span id="newDateSpan"></span><br><span id="oldDateSpan"></span></p>_x000D_

How to add jQuery code into HTML Page

for latest Jquery. Simply:

<script src=""></script>

How to Get XML Node from XDocument

The .Elements operation returns a LIST of XElements - but what you really want is a SINGLE element. Add this:

XElement Contacts = (from xml2 in XMLDoc.Elements("Contacts").Elements("Node")
                    where xml2.Element("ID").Value == variable
                    select xml2).FirstOrDefault();

This way, you tell LINQ to give you the first (or NULL, if none are there) from that LIST of XElements you're selecting.


Removing NA in dplyr pipe

I don't think desc takes an na.rm argument... I'm actually surprised it doesn't throw an error when you give it one. If you just want to remove NAs, use na.omit (base) or tidyr::drop_na:

outcome.df %>%
  na.omit() %>%
  group_by(Hospital, State) %>%
  arrange(desc(HeartAttackDeath)) %>%

outcome.df %>%
  drop_na() %>%
  group_by(Hospital, State) %>%
  arrange(desc(HeartAttackDeath)) %>%

If you only want to remove NAs from the HeartAttackDeath column, filter with, or use tidyr::drop_na:

outcome.df %>%
  filter(! %>%
  group_by(Hospital, State) %>%
  arrange(desc(HeartAttackDeath)) %>%

outcome.df %>%
  drop_na(HeartAttackDeath) %>%
  group_by(Hospital, State) %>%
  arrange(desc(HeartAttackDeath)) %>%

As pointed out at the dupe, complete.cases can also be used, but it's a bit trickier to put in a chain because it takes a data frame as an argument but returns an index vector. So you could use it like this:

outcome.df %>%
  filter(complete.cases(.)) %>%
  group_by(Hospital, State) %>%
  arrange(desc(HeartAttackDeath)) %>%

Update TextView Every Second

Add following code in your onCreate() method:

Thread thread = new Thread() {

  public void run() {
    try {
      while (!thread.isInterrupted()) {
        runOnUiThread(new Runnable() {
          public void run() {
            // update TextView here!
    } catch (InterruptedException e) {


This code starts an thread which sleeps 1000 milliseconds every round.

jQuery - replace all instances of a character in a string

You need to use a regular expression, so that you can specify the global (g) flag:

var s = 'some+multi+word+string'.replace(/\+/g, ' ');

(I removed the $() around the string, as replace is not a jQuery method, so that won't work at all.)

Editing dictionary values in a foreach loop

If you're feeling creative you could do something like this. Loop backwards through the dictionary to make your changes.

Dictionary<string, int> collection = new Dictionary<string, int>();
collection.Add("value1", 9);
collection.Add("value2", 7);
collection.Add("value3", 5);
collection.Add("value4", 3);
collection.Add("value5", 1);

for (int i = collection.Keys.Count; i-- > 0; ) {
    if (collection.Values.ElementAt(i) < 5) {
        collection.Remove(collection.Keys.ElementAt(i)); ;


Certainly not identical, but you might be interested anyways...

SQL permissions for roles

Unless the role was made dbo, db_owner or db_datawriter, it won't have permission to edit any data. If you want to grant full edit permissions to a single table, do this:

GRANT ALL ON table1 TO doctor 

Users in that role will have no permissions whatsoever to other tables (not even read).

Creating watermark using html and css

I would recommend everyone look into CSS grids. It has been supported by most browsers now since about 2017. Here is a link to some documentation: . It is so much easier to keep your page elements where you want them, especially when it comes to responsiveness. It took me all of 20 minutes to learn how to do it, and I'm a newbie!

<div class="grid-div">
    <p class="hello">Hello</p>
    <p class="world">World</p>

//begin css//

.grid-div {
    display: grid;
    grid-template-columns: 50% 50%;
    grid-template-rows: 50% 50%;

.hello {
    grid-column-start: 2;
    grid-row-start: 2;

.world {
    grid-column-start: 1;
    grid-row-start: 2;

This code will split the page into 4 equal quadrants, placing the "Hello" in the bottom right, and the "World" in the bottom left without having to change their positioning or playing with margins.

This can be extrapolated into very complex grid layouts with overlapping, infinite grids of all sizes, and even grids nested inside grids, without losing control of your elements every time something changes (MS Word I'm looking at you).

Hope this helps whoever still needs it!

What are the differences between ArrayList and Vector?

Vector is a broken class that is not threadsafe, despite it being "synchronized" and is only used by students and other inexperienced programmers.

ArrayList is the go-to List implementation used by professionals and experienced programmers.

Professionals wanting a threadsafe List implementation use a CopyOnWriteArrayList.

'dict' object has no attribute 'has_key'

In python3, has_key(key) is replaced by __contains__(key)

Tested in python3.7:

a = {'a':1, 'b':2, 'c':3}

ITextSharp insert text to an existing pdf

I found a way to do it (dont know if it is the best but it works)

string oldFile = "oldFile.pdf";
string newFile = "newFile.pdf";

// open the reader
PdfReader reader = new PdfReader(oldFile);
Rectangle size = reader.GetPageSizeWithRotation(1);
Document document = new Document(size);

// open the writer
FileStream fs = new FileStream(newFile, FileMode.Create, FileAccess.Write);
PdfWriter writer = PdfWriter.GetInstance(document, fs);

// the pdf content
PdfContentByte cb = writer.DirectContent;

// select the font properties
BaseFont bf = BaseFont.CreateFont(BaseFont.HELVETICA, BaseFont.CP1252,BaseFont.NOT_EMBEDDED);
cb.SetFontAndSize(bf, 8);

// write the text in the pdf content
string text = "Some random blablablabla...";
// put the alignment and coordinates here
cb.ShowTextAligned(1, text, 520, 640, 0);
text = "Other random blabla...";
// put the alignment and coordinates here
cb.ShowTextAligned(2, text, 100, 200, 0);

// create the new page and add it to the pdf
PdfImportedPage page = writer.GetImportedPage(reader, 1);
cb.AddTemplate(page, 0, 0);

// close the streams and voilá the file should be changed :)

I hope this can be usefull for someone =) (and post here any errors)

How to implement a tree data-structure in Java?

You can use TreeSet class in java.util.*. It is working like Binary search tree, so it is already sorted. TreeSet class implements Iterable, Collection and Set interfaces. You can traverse through the tree with iterator like a set.

TreeSet<String> treeSet = new TreeSet<String>();
Iterator<String> it  = treeSet.Iterator();

You can check, Java Doc and some other .

Invert "if" statement to reduce nesting

Performance is in two parts. You have performance when the software is in production, but you also want to have performance while developing and debugging. The last thing a developer wants is to "wait" for something trivial. In the end, compiling this with optimization enabled will result in similar code. So it's good to know these little tricks that pay off in both scenarios.

The case in the question is clear, ReSharper is correct. Rather than nesting if statements, and creating new scope in code, you're setting a clear rule at the start of your method. It increases readability, it will be easier to maintain, and it reduces the amount of rules one has to sift through to find where they want to go.

How to fix 'android.os.NetworkOnMainThreadException'?

This exception occurs due to any heavy task performed on the main thread if that performing task takes too much time.

To avoid this, we can handle it using threads or executers

Executors.newSingleThreadExecutor().submit(new Runnable() {
    public void run() {
        // You can perform your task here.

how to refresh my datagridview after I add new data

reload the form

Form1_Load(sender, e)

How to search a string in a single column (A) in excel using VBA

Below are two methods that are superior to looping. Both handle a "no-find" case.

  1. The VBA equivalent of a normal function VLOOKUP with error-handling if the variable doesn't exist (INDEX/MATCH may be a better route than VLOOKUP, ie if your two columns A and B were in reverse order, or were far apart)
  2. VBAs FIND method (matching a whole string in column A given I use the xlWhole argument)

    Sub Method1()
    Dim strSearch As String
    Dim strOut As String
    Dim bFailed As Boolean
    strSearch = "trees"
    On Error Resume Next
    strOut = Application.WorksheetFunction.VLookup(strSearch, Range("A:B"), 2, False)
    If Err.Number <> 0 Then bFailed = True
    On Error GoTo 0
    If Not bFailed Then
    MsgBox "corresponding value is " & vbNewLine & strOut
    MsgBox strSearch & " not found"
    End If
    End Sub
    Sub Method2()
        Dim rng1 As Range
        Dim strSearch As String
        strSearch = "trees"
        Set rng1 = Range("A:A").Find(strSearch, , xlValues, xlWhole)
        If Not rng1 Is Nothing Then
            MsgBox "Find has matched " & strSearch & vbNewLine & "corresponding cell is " & rng1.Offset(0, 1)
            MsgBox strSearch & " not found"
        End If
    End Sub

jquery clear input default value

Try that:

  var defaultEmailNews = "Email address";
  $('input[name=email]').focus(function() {
    if($(this).val() == defaultEmailNews) $(this).val("");

  $('input[name=email]').focusout(function() {
    if($(this).val() == "") $(this).val(defaultEmailNews);

moment.js - UTC gives wrong date

Both Date and moment will parse the input string in the local time zone of the browser by default. However Date is sometimes inconsistent with this regard. If the string is specifically YYYY-MM-DD, using hyphens, or if it is YYYY-MM-DD HH:mm:ss, it will interpret it as local time. Unlike Date, moment will always be consistent about how it parses.

The correct way to parse an input moment as UTC in the format you provided would be like this:

moment.utc('07-18-2013', 'MM-DD-YYYY')

Refer to this documentation.

If you want to then format it differently for output, you would do this:

moment.utc('07-18-2013', 'MM-DD-YYYY').format('YYYY-MM-DD')

You do not need to call toString explicitly.

Note that it is very important to provide the input format. Without it, a date like 01-04-2013 might get processed as either Jan 4th or Apr 1st, depending on the culture settings of the browser.

Getting the first character of a string with $str[0]

In case of multibyte (unicode) strings using str[0] can cause a trouble. mb_substr() is a better solution. For example:

$first_char = mb_substr($title, 0, 1);

Some details here: Get first character of UTF-8 string

Creating a fixed sidebar alongside a centered Bootstrap 3 grid

As drew_w said, you can find a good example here.


<div id="wrapper">
    <div id="sidebar-wrapper">
        <ul class="sidebar-nav">
            <li class="sidebar-brand"><a href="#">Home</a></li>
            <li><a href="#">Another link</a></li>
            <li><a href="#">Next link</a></li>
            <li><a href="#">Last link</a></li>
    <div id="page-content-wrapper">
        <div class="page-content">
            <div class="container">
                <div class="row">
                    <div class="col-md-12">
                        <!-- content of page -->


#wrapper {
  padding-left: 250px;
  transition: all 0.4s ease 0s;

#sidebar-wrapper {
  margin-left: -250px;
  left: 250px;
  width: 250px;
  background: #CCC;
  position: fixed;
  height: 100%;
  overflow-y: auto;
  z-index: 1000;
  transition: all 0.4s ease 0s;

#page-content-wrapper {
  width: 100%;

.sidebar-nav {
  position: absolute;
  top: 0;
  width: 250px;
  list-style: none;
  margin: 0;
  padding: 0;

@media (max-width:767px) {

    #wrapper {
      padding-left: 0;

    #sidebar-wrapper {
      left: 0;
    } {
      position: relative;
      left: 250px;
    } #sidebar-wrapper {
      left: 250px;
      width: 250px;
      transition: all 0.4s ease 0s;



How can I kill all sessions connecting to my oracle database?


startup force;

Brutal, yet elegant.

finding and replacing elements in a list

I know this is a very old question and there's a myriad of ways to do it. The simpler one I found is using numpy package.

import numpy

arr = numpy.asarray([1, 6, 1, 9, 8])
arr[ arr == 8 ] = 0 # change all occurrences of 8 by 0

Determine what attributes were changed in Rails after_save callback?

To anyone seeing this later on, as it currently (Aug. 2017) tops google: It is worth mentioning, that this behavior will be altered in Rails 5.2, and has deprecation warnings as of Rails 5.1, as ActiveModel::Dirty changed a bit.

What do I change?

If you're using attribute_changed? method in the after_*-callbacks, you'll see a warning like:

DEPRECATION WARNING: The behavior of attribute_changed? inside of after callbacks will be changing in the next version of Rails. The new return value will reflect the behavior of calling the method after save returned (e.g. the opposite of what it returns now). To maintain the current behavior, use saved_change_to_attribute? instead. (called from some_callback at /PATH_TO/app/models/user.rb:15)

As it mentions, you could fix this easily by replacing the function with saved_change_to_attribute?. So for example, name_changed? becomes saved_change_to_name?.

Likewise, if you're using the attribute_change to get the before-after values, this changes as well and throws the following:

DEPRECATION WARNING: The behavior of attribute_change inside of after callbacks will be changing in the next version of Rails. The new return value will reflect the behavior of calling the method after save returned (e.g. the opposite of what it returns now). To maintain the current behavior, use saved_change_to_attribute instead. (called from some_callback at /PATH_TO/app/models/user.rb:20)

Again, as it mentions, the method changes name to saved_change_to_attribute which returns ["old", "new"]. or use saved_changes, which returns all the changes, and these can be accessed as saved_changes['attribute'].

What does the servlet <load-on-startup> value signify

  1. If value is same for two servlet than they will be loaded in an order on which they are declared inside web.xml file.
  2. if is 0 or negative integer than Servlet will be loaded when Container feels to load them.
  3. guarantees loading, initialization and call to init() method of servlet by web container.
  4. If there is no element for any servlet than they will be loaded when web container decides to load them.

Find if listA contains any elements not in listB

listA.Any(_ => listB.Contains(_))


Count the number of commits on a Git branch

To count the commits for the branch you are on:

git rev-list --count HEAD

for a branch

git rev-list --count <branch-name>

If you want to count the commits on a branch that are made since you created the branch

git rev-list --count HEAD ^<branch-name>

This will count all commits ever made that are not on the branch-name as well.


git checkout master
git checkout -b test
<We do 3 commits>
git rev-list --count HEAD ^master

Result: 3

If your branch comes of a branch called develop:

git checkout develop
git checkout -b test
<We do 3 commits>
git rev-list --count HEAD ^develop

Result: 3

Ignoring Merges

If you merge another branch into the current branch without fast forward and you do the above, the merge is also counted. This is because for git a merge is a commit.

If you don't want to count these commits add --no-merges:

git rev-list --no-merges --count HEAD ^develop

Padding between ActionBar's home icon and title

Using titleMarginStart works for me. Xamarin example:


Set the logo like so:

mToolbar = FindViewById<SupportToolbar>(Resource.Id.toolbar);
SupportActionBar.Title = "App title";

How to check list A contains any value from list B?

If you didn't care about performance, you could try:

a.Any(item => b.Contains(item))
// or, as in the column using a method group

But I would try this first:


jQuery Validate Plugin - How to create a simple custom rule?

Step 1 Included the cdn like

     <script src=""></script>

     <script src=""></script>

Step 2 Code Like

        $("#submit").click(function () {
              $('#myform').validate({ // initialize the plugin
                rules: {
                    id: {
                        required: true,
                        email: true
                    password: {
                        required: true,
                        minlength: 1
                messages: {
                    id: {
                        required: "Enter Email Id"

                    password: {
                        required: "Enter Email Password"

                submitHandler: function (form) { // for demo
                    alert('valid form submitted'); // for demo
                    return false; // for demo

String Concatenation in EL

With EL 2 you can do the following:

#{'this'.concat(' is').concat(' a').concat(' test!')}

ASP.NET MVC - Set custom IIdentity or IPrincipal

Here's how I do it.

I decided to use IPrincipal instead of IIdentity because it means I don't have to implement both IIdentity and IPrincipal.

  1. Create the interface

    interface ICustomPrincipal : IPrincipal
        int Id { get; set; }
        string FirstName { get; set; }
        string LastName { get; set; }
  2. CustomPrincipal

    public class CustomPrincipal : ICustomPrincipal
        public IIdentity Identity { get; private set; }
        public bool IsInRole(string role) { return false; }
        public CustomPrincipal(string email)
            this.Identity = new GenericIdentity(email);
        public int Id { get; set; }
        public string FirstName { get; set; }
        public string LastName { get; set; }
  3. CustomPrincipalSerializeModel - for serializing custom information into userdata field in FormsAuthenticationTicket object.

    public class CustomPrincipalSerializeModel
        public int Id { get; set; }
        public string FirstName { get; set; }
        public string LastName { get; set; }
  4. LogIn method - setting up a cookie with custom information

    if (Membership.ValidateUser(viewModel.Email, viewModel.Password))
        var user = userRepository.Users.Where(u => u.Email == viewModel.Email).First();
        CustomPrincipalSerializeModel serializeModel = new CustomPrincipalSerializeModel();
        serializeModel.Id = user.Id;
        serializeModel.FirstName = user.FirstName;
        serializeModel.LastName = user.LastName;
        JavaScriptSerializer serializer = new JavaScriptSerializer();
        string userData = serializer.Serialize(serializeModel);
        FormsAuthenticationTicket authTicket = new FormsAuthenticationTicket(
        string encTicket = FormsAuthentication.Encrypt(authTicket);
        HttpCookie faCookie = new HttpCookie(FormsAuthentication.FormsCookieName, encTicket);
        return RedirectToAction("Index", "Home");
  5. Global.asax.cs - Reading cookie and replacing HttpContext.User object, this is done by overriding PostAuthenticateRequest

    protected void Application_PostAuthenticateRequest(Object sender, EventArgs e)
        HttpCookie authCookie = Request.Cookies[FormsAuthentication.FormsCookieName];
        if (authCookie != null)
            FormsAuthenticationTicket authTicket = FormsAuthentication.Decrypt(authCookie.Value);
            JavaScriptSerializer serializer = new JavaScriptSerializer();
            CustomPrincipalSerializeModel serializeModel = serializer.Deserialize<CustomPrincipalSerializeModel>(authTicket.UserData);
            CustomPrincipal newUser = new CustomPrincipal(authTicket.Name);
            newUser.Id = serializeModel.Id;
            newUser.FirstName = serializeModel.FirstName;
            newUser.LastName = serializeModel.LastName;
            HttpContext.Current.User = newUser;
  6. Access in Razor views

    @((User as CustomPrincipal).Id)
    @((User as CustomPrincipal).FirstName)
    @((User as CustomPrincipal).LastName)

and in code:

    (User as CustomPrincipal).Id
    (User as CustomPrincipal).FirstName
    (User as CustomPrincipal).LastName

I think the code is self-explanatory. If it isn't, let me know.

Additionally to make the access even easier you can create a base controller and override the returned User object (HttpContext.User):

public class BaseController : Controller
    protected virtual new CustomPrincipal User
        get { return HttpContext.User as CustomPrincipal; }

and then, for each controller:

public class AccountController : BaseController
    // ...

which will allow you to access custom fields in code like this:


But this will not work inside views. For that you would need to create a custom WebViewPage implementation:

public abstract class BaseViewPage : WebViewPage
    public virtual new CustomPrincipal User
        get { return base.User as CustomPrincipal; }

public abstract class BaseViewPage<TModel> : WebViewPage<TModel>
    public virtual new CustomPrincipal User
        get { return base.User as CustomPrincipal; }

Make it a default page type in Views/web.config:

<pages pageBaseType="Your.Namespace.BaseViewPage">
    <add namespace="System.Web.Mvc" />
    <add namespace="System.Web.Mvc.Ajax" />
    <add namespace="System.Web.Mvc.Html" />
    <add namespace="System.Web.Routing" />

and in views, you can access it like this:


Can IntelliJ IDEA encapsulate all of the functionality of WebStorm and PHPStorm through plugins?

But here's the rub, sometimes you can't or don't want to wait. For example I want to use the new support for RubyMotion which includes RubyMotion project structure support, setup of rake files, setup of configurations that are hooked to iOS Simulator etc.

RubyMine has all of these now, IDEA does not. So I would have to generate a RubyMotion project outside of IDEA, then setup an IDEA project and hook up to that source folder etc and God knows what else.

What JetBrains should do is have a licensing model that would allow me, with the purchase of IDEA to use any of other IDEs, as opposed to just relying on IDEAs plugins.

I would be willing to pay more for that i.e. say 50 bucks more for said flexibility.

The funny thing is, I was originally a RubyMine customer that upgraded to IDEA, because I did want that polyglot setup. Now I'm contemplating paying for the upgrade of RubyMine, just because I need to do RubyMotion now. Also there are other potential areas where this out of sync issue might bite me again . For example torque box workflow / deployment support.

JetBrains has good IDEs but I guess I'm a bit annoyed.

Python: Split a list into sub-lists based on index ranges

In python, it's called slicing. Here is an example of python's slice notation:

>>> list1 = ['a','b','c','d','e','f','g','h', 'i', 'j', 'k', 'l']
>>> print list1[:5]
['a', 'b', 'c', 'd', 'e']
>>> print list1[-7:]
['f', 'g', 'h', 'i', 'j', 'k', 'l']

Note how you can slice either positively or negatively. When you use a negative number, it means we slice from right to left.

How to detect browser using angularjs?

Why not use document.documentMode only available under IE:

var doc = $window.document;
if (!!doc.documentMode)
  if (doc.documentMode === 10)
    doc.documentElement.className += ' isIE isIE10';
  else if (doc.documentMode === 11)
    doc.documentElement.className += ' isIE isIE11';
  // etc.

How do I upload a file with the JS fetch API?

The accepted answer here is a bit dated. As of April 2020, a recommended approach seen on the MDN website suggests using FormData and also does not ask to set the content type.

I'm quoting the code snippet for convenience:

const formData = new FormData();
const fileField = document.querySelector('input[type="file"]');

formData.append('username', 'abc123');
formData.append('avatar', fileField.files[0]);

fetch('', {
  method: 'PUT',
  body: formData
.then((response) => response.json())
.then((result) => {
  console.log('Success:', result);
.catch((error) => {
  console.error('Error:', error);

Set a Fixed div to 100% width of the parent container

You can use margin for .wrap container instead of padding for .wrapper:

body{ height:20000px }
#wrapper { padding: 0%; }
    float: left;
    position: relative;
    margin: 10%;
    width: 40%; 


Reset ID autoincrement ? phpmyadmin

I agree with rpd, this is the answer and can be done on a regular basis to clean up your id column that is getting bigger with only a few hundred rows of data, but maybe an id of 34444543!, as the data is deleted out regularly but id is incremented automatically.


The above sql can be run via sql query or as php. This will delete the id column.

Then re add it again, via the code below:


Place this in a piece of code that may get run maybe in an admin panel, so when anyone enters that page it will run this script that auto cleans your database, and tidys it.

Using column alias in WHERE clause of MySQL query produces an error

Maybe my answer is too late but this can help others.

You can enclose it with another select statement and use where clause to it.

SELECT * FROM (Select col1, col2,...) as t WHERE t.calcAlias > 0

calcAlias is the alias column that was calculated.

OS X Framework Library not loaded: 'Image not found'

Xcode 11 :

in Xcode 11 add framework into General->Frameworks, Libraries And Embedded Content

after adding make sure you select Embed & Sign option

enter image description here

How to bind WPF button to a command in ViewModelBase?

 <Grid >
        <ColumnDefinition Width="*"/>
    <Button Command="{Binding ClickCommand}" Width="100" Height="100" Content="wefwfwef"/>

the code behind for the window:

public partial class MainWindow : Window
    public MainWindow()
        DataContext = new ViewModelBase();

The ViewModel:

public class ViewModelBase
    private ICommand _clickCommand;
    public ICommand ClickCommand
            return _clickCommand ?? (_clickCommand = new CommandHandler(() => MyAction(), ()=> CanExecute));
     public bool CanExecute
            // check if executing is allowed, i.e., validate, check if a process is running, etc. 
            return true/false;

    public void MyAction()


Command Handler:

 public class CommandHandler : ICommand
    private Action _action;
    private Func<bool> _canExecute;

    /// <summary>
    /// Creates instance of the command handler
    /// </summary>
    /// <param name="action">Action to be executed by the command</param>
    /// <param name="canExecute">A bolean property to containing current permissions to execute the command</param>
    public CommandHandler(Action action, Func<bool> canExecute)
        _action = action;
        _canExecute = canExecute;

    /// <summary>
    /// Wires CanExecuteChanged event 
    /// </summary>
    public event EventHandler CanExecuteChanged
        add { CommandManager.RequerySuggested += value; }
        remove { CommandManager.RequerySuggested -= value; }

    /// <summary>
    /// Forcess checking if execute is allowed
    /// </summary>
    /// <param name="parameter"></param>
    /// <returns></returns>
    public bool CanExecute(object parameter)
        return _canExecute.Invoke();

    public void Execute(object parameter)

I hope this will give you the idea.

jackson deserialization json to java-objects

It looks like you are trying to read an object from JSON that actually describes an array. Java objects are mapped to JSON objects with curly braces {} but your JSON actually starts with square brackets [] designating an array.

What you actually have is a List<product> To describe generic types, due to Java's type erasure, you must use a TypeReference. Your deserialization could read: myProduct = objectMapper.readValue(productJson, new TypeReference<List<product>>() {});

A couple of other notes: your classes should always be PascalCased. Your main method can just be public static void main(String[] args) throws Exception which saves you all the useless catch blocks.

How do I add a library project to Android Studio?

Here is the visual guide:

Update for Android Studio 0.8.2:

In Android Studio 0.8.2, go to Project Structure -> under Modules just hit the plus button and select Import Existing Project and import actionbarsherlock. Then synchronise your Gradle files.

If you face the error

Error: The SDK Build Tools revision (xx.x.x) is too low. Minimum required is yy.y.y

just open the build.gradle file in actionbarsherlock directory and update the buildToolsVersion to the suggested one.

android {
  compileSdkVersion 19
  buildToolsVersion 'yy.y.y'

Android Studio 0.8.2

Menu File -> Project Structure...:


Module -> Import Module


After importing the library module, select your project module and add the dependency:


And then select the imported module:


JavaScript: Alert.Show(message) From ASP.NET Code-behind

string script = "<script type="text/javascript">alert('" + cleanMessage + "');</script>"; 

You should use string.Format in this case. This is better coding style. For you it would be:

string script = string.Format(@"<script type='text/javascript'>alert('{0}');</script>");

Also note that when you should escape " symbol or use apostroph instead.

Why not inherit from List<T>?

Prefer Interfaces over Classes

Classes should avoid deriving from classes and instead implement the minimal interfaces necessary.

Inheritance breaks Encapsulation

Deriving from classes breaks encapsulation:

  • exposes internal details about how your collection is implemented
  • declares an interface (set of public functions and properties) that may not be appropriate

Among other things this makes it harder to refactor your code.

Classes are an Implementation Detail

Classes are an implementation detail that should be hidden from other parts of your code. In short a System.List is a specific implementation of an abstract data type, that may or may not be appropriate now and in the future.

Conceptually the fact that the System.List data type is called "list" is a bit of a red-herring. A System.List<T> is a mutable ordered collection that supports amortized O(1) operations for adding, inserting, and removing elements, and O(1) operations for retrieving the number of elements or getting and setting element by index.

The Smaller the Interface the more Flexible the Code

When designing a data structure, the simpler the interface is, the more flexible the code is. Just look at how powerful LINQ is for a demonstration of this.

How to Choose Interfaces

When you think "list" you should start by saying to yourself, "I need to represent a collection of baseball players". So let's say you decide to model this with a class. What you should do first is decide what the minimal amount of interfaces that this class will need to expose.

Some questions that can help guide this process:

  • Do I need to have the count? If not consider implementing IEnumerable<T>
  • Is this collection going to change after it has been initialized? If not consider IReadonlyList<T>.
  • Is it important that I can access items by index? Consider ICollection<T>
  • Is the order in which I add items to the collection important? Maybe it is an ISet<T>?
  • If you indeed want these thing then go ahead and implement IList<T>.

This way you will not be coupling other parts of the code to implementation details of your baseball players collection and will be free to change how it is implemented as long as you respect the interface.

By taking this approach you will find that code becomes easier to read, refactor, and reuse.

Notes about Avoiding Boilerplate

Implementing interfaces in a modern IDE should be easy. Right click and choose "Implement Interface". Then forward all of the implementations to a member class if you need to.

That said, if you find you are writing lots of boilerplate, it is potentially because you are exposing more functions than you should be. It is the same reason you shouldn't inherit from a class.

You can also design smaller interfaces that make sense for your application, and maybe just a couple of helper extension functions to map those interfaces to any others that you need. This is the approach I took in my own IArray interface for the LinqArray library.

How to declare Global Variables in Excel VBA to be visible across the Workbook

You can do the following to learn/test the concept:

  1. Open new Excel Workbook and in Excel VBA editor right-click on Modules->Insert->Module

  2. In newly added Module1 add the declaration; Public Global1 As String

  3. in Worksheet VBA Module Sheet1(Sheet1) put the code snippet:

Sub setMe()
      Global1 = "Hello"
End Sub
  1. in Worksheet VBA Module Sheet2(Sheet2) put the code snippet:
Sub showMe()
    Debug.Print (Global1)
End Sub
  1. Run in sequence Sub setMe() and then Sub showMe() to test the global visibility/accessibility of the var Global1

Hope this will help.

How to directly initialize a HashMap (in a literal way)?

All Versions

In case you happen to need just a single entry: There is Collections.singletonMap("key", "value").

For Java Version 9 or higher:

Yes, this is possible now. In Java 9 a couple of factory methods have been added that simplify the creation of maps :

// this works for up to 10 elements:
Map<String, String> test1 = Map.of(
    "a", "b",
    "c", "d"

// this works for any number of elements:
import static java.util.Map.entry;    
Map<String, String> test2 = Map.ofEntries(
    entry("a", "b"),
    entry("c", "d")

In the example above both test and test2 will be the same, just with different ways of expressing the Map. The Map.of method is defined for up to ten elements in the map, while the Map.ofEntries method will have no such limit.

Note that in this case the resulting map will be an immutable map. If you want the map to be mutable, you could copy it again, e.g. using mutableMap = new HashMap<>(Map.of("a", "b"));

(See also JEP 269 and the Javadoc)

For up to Java Version 8:

No, you will have to add all the elements manually. You can use an initializer in an anonymous subclass to make the syntax a little bit shorter:

Map<String, String> myMap = new HashMap<String, String>() {{
        put("a", "b");
        put("c", "d");

However, the anonymous subclass might introduce unwanted behavior in some cases. This includes for example:

  • It generates an additional class which increases memory consumption, disk space consumption and startup-time
  • In case of a non-static method: It holds a reference to the object the creating method was called upon. That means the object of the outer class cannot be garbage collected while the created map object is still referenced, thus blocking additional memory

Using a function for initialization will also enable you to generate a map in an initializer, but avoids nasty side-effects:

Map<String, String> myMap = createMap();

private static Map<String, String> createMap() {
    Map<String,String> myMap = new HashMap<String,String>();
    myMap.put("a", "b");
    myMap.put("c", "d");
    return myMap;

return value after a promise

Use a pattern along these lines:

function getValue(file) {
  return lookupValue(file);

getValue('myFile.txt').then(function(res) {
  // do whatever with res here

(although this is a bit redundant, I'm sure your actual code is more complicated)

cmake and libpthread

@Manuel was part way there. You can add the compiler option as well, like this:

If you have CMake 3.1.0+, this becomes even easier:

find_package(Threads REQUIRED)
target_link_libraries(my_app PRIVATE Threads::Threads)

If you are using CMake 2.8.12+, you can simplify this to:

find_package(Threads REQUIRED)
  target_compile_options(my_app PUBLIC "-pthread")
  target_link_libraries(my_app "${CMAKE_THREAD_LIBS_INIT}")

Older CMake versions may require:

find_package(Threads REQUIRED)
  set_property(TARGET my_app PROPERTY COMPILE_OPTIONS "-pthread")
  set_property(TARGET my_app PROPERTY INTERFACE_COMPILE_OPTIONS "-pthread")
  target_link_libraries(my_app "${CMAKE_THREAD_LIBS_INIT}")

If you want to use one of the first two methods with CMake 3.1+, you will need set(THREADS_PREFER_PTHREAD_FLAG ON) there too.

How do I raise an exception in Rails so it behaves like other Rails exceptions?

If you need an easier way to do it, and don't want much fuss, a simple execution could be:

raise'something bad happened!')

This will raise an exception, say e with e.message = something bad happened!

and then you can rescue it as you are rescuing all other exceptions in general.

Is it ok to run docker from inside docker?

Running Docker inside Docker (a.k.a. dind), while possible, should be avoided, if at all possible. (Source provided below.) Instead, you want to set up a way for your main container to produce and communicate with sibling containers.

Jérôme Petazzoni — the author of the feature that made it possible for Docker to run inside a Docker container — actually wrote a blog post saying not to do it. The use case he describes matches the OP's exact use case of a CI Docker container that needs to run jobs inside other Docker containers.

Petazzoni lists two reasons why dind is troublesome:

  1. It does not cooperate well with Linux Security Modules (LSM).
  2. It creates a mismatch in file systems that creates problems for the containers created inside parent containers.

From that blog post, he describes the following alternative,

[The] simplest way is to just expose the Docker socket to your CI container, by bind-mounting it with the -v flag.

Simply put, when you start your CI container (Jenkins or other), instead of hacking something together with Docker-in-Docker, start it with:

docker run -v /var/run/docker.sock:/var/run/docker.sock ...

Now this container will have access to the Docker socket, and will therefore be able to start containers. Except that instead of starting "child" containers, it will start "sibling" containers.

How to read a text file in project's root directory?

In this code you access to root directory project:

 string _filePath = Path.GetDirectoryName(System.AppDomain.CurrentDomain.BaseDirectory);


StreamReader r = new StreamReader(_filePath + "/cities2.json"))

Server.MapPath("."), Server.MapPath("~"), Server.MapPath(@"\"), Server.MapPath("/"). What is the difference?

Server.MapPath specifies the relative or virtual path to map to a physical directory.

  • Server.MapPath(".")1 returns the current physical directory of the file (e.g. aspx) being executed
  • Server.MapPath("..") returns the parent directory
  • Server.MapPath("~") returns the physical path to the root of the application
  • Server.MapPath("/") returns the physical path to the root of the domain name (is not necessarily the same as the root of the application)

An example:

Let's say you pointed a web site application ( to


and installed your shop application (sub web as virtual directory in IIS, marked as application) in


For example, if you call Server.MapPath() in following request:


  • Server.MapPath(".")1 returns D:\WebApps\shop\products
  • Server.MapPath("..") returns D:\WebApps\shop
  • Server.MapPath("~") returns D:\WebApps\shop
  • Server.MapPath("/") returns C:\Inetpub\wwwroot
  • Server.MapPath("/shop") returns D:\WebApps\shop

If Path starts with either a forward slash (/) or backward slash (\), the MapPath() returns a path as if Path was a full, virtual path.

If Path doesn't start with a slash, the MapPath() returns a path relative to the directory of the request being processed.

Note: in C#, @ is the verbatim literal string operator meaning that the string should be used "as is" and not be processed for escape sequences.


  1. Server.MapPath(null) and Server.MapPath("") will produce this effect too.

How do I get a list of folders and sub folders without the files?

I don't have enough reputation to comment on any answer. In one of the comments, someone has asked how to ignore the hidden folders in the list. Below is how you can do this.

dir /b /AD-H

How to select first and last TD in a row?

You can use the following snippet:

  tr td:first-child {text-decoration: underline;}
  tr td:last-child {color: red;}

Using the following pseudo classes:

:first-child means "select this element if it is the first child of its parent".

:last-child means "select this element if it is the last child of its parent".

Only element nodes (HTML tags) are affected, these pseudo-classes ignore text nodes.

What is the difference between Cloud Computing and Grid Computing?

Cloud Computing is For Service Oriented where as Grid Computing is for Application Oriented. Grid computing is used to build Virtual supercomputer using a middler ware to achieve a common task that can be shared among several resources. most probably this task will be kind of computing or data storage.

Cloud computing is providing services over the internet through several servers uses Virtualization.In cloud computing either you can provide service in three types Iaas , Paas, Saas . This will give you solution when you don't have any resources for a short time Business service over the Internet.

AlertDialog.Builder with custom layout and EditText; cannot access view

You can write:

AlertDialog.Builder dialogBuilder = new AlertDialog.Builder(this);

 // ...Irrelevant code for customizing the buttons and title

LayoutInflater inflater = this.getLayoutInflater(); 

View dialogView= inflater.inflate(R.layout.alert_label_editor, null);                    

Button button = (Button)dialogView.findViewById(;

   button.setOnClickListener(new View.OnClickListener() {
       public void onClick(View view) {

         //Commond here......


EditText editText = (EditText)

editText.setText("test label"); 


Memcache Vs. Memcached

They are not identical. Memcache is older but it has some limitations. I was using just fine in my application until I realized you can't store literal FALSE in cache. Value FALSE returned from the cache is the same as FALSE returned when a value is not found in the cache. There is no way to check which is which. Memcached has additional method (among others) Memcached::getResultCode that will tell you whether key was found.

Because of this limitation I switched to storing empty arrays instead of FALSE in cache. I am still using Memcache, but I just wanted to put this info out there for people who are deciding.

Combine a list of data frames into one data frame by row

For the purpose of completeness, I thought the answers to this question required an update. "My guess is that using"rbind", ...) is going to be the fastest approach that you will find..." It was probably true for May 2010 and some time after, but in about Sep 2011 a new function rbindlist was introduced in the data.table package version 1.8.2, with a remark that "This does the same as"rbind",l), but much faster". How much faster?

benchmark( ="rbind", listOfDataFrames),
  plyr_rbind.fill = plyr::rbind.fill(listOfDataFrames), 
  plyr_ldply = plyr::ldply(listOfDataFrames, data.frame),
  data.table_rbindlist =,
  replications = 100, order = "relative", 
  columns=c('test','replications', 'elapsed','relative')

                  test replications elapsed relative
4 data.table_rbindlist          100    0.11    1.000
1              100    9.39   85.364
2      plyr_rbind.fill          100   12.08  109.818
3           plyr_ldply          100   15.14  137.636

Java array assignment (multiple values)

int a[] = { 2, 6, 8, 5, 4, 3 }; 
int b[] = { 2, 3, 4, 7 };

if you take float number then you take float and it's your choice

this is very good way to show array elements.

How can I create Min stl priority_queue?

In C++11 you could also create an alias for convenience:

template<class T> using min_heap = priority_queue<T, std::vector<T>, std::greater<T>>;

And use it like this:

min_heap<int> my_heap;

How to write a CSS hack for IE 11?

You can use the following code inside the style tag:

@media screen and (-ms-high-contrast: active), (-ms-high-contrast: none) {  
/* IE10+ specific styles go here */  

Below is an example that worked for me:

<style type="text/css">

@media screen and (-ms-high-contrast: active), (-ms-high-contrast: none) {  
   /* IE10+ specific styles go here */  
   #flashvideo {
        margin:-240px 0 0 350px;

    #googleMap {
        margin:-515px 0 0 350px;

#nav li {

#nav a {

Please note that since (#nav li) and (#nav a) are outside of the @media screen ..., they are general styles.

Parsing a JSON string in Ruby

This looks like JavaScript Object Notation (JSON). You can parse JSON that resides in some variable, e.g. json_string, like so:

require 'json'

If you’re using an older Ruby, you may need to install the json gem.

There are also other implementations of JSON for Ruby that may fit some use-cases better:

How do I get the offset().top value of an element without using jQuery?

For Angular 2+ to get the offset of the current element (this.el.nativeElement is equvalent of $(this) in jquery):

export class MyComponent implements  OnInit {

constructor(private el: ElementRef) {}

    ngOnInit() {
      //This is the important line you can use in your function in the code
        let offset = this.el.nativeElement.getBoundingClientRect().top;



LINQ: Select an object and change some properties without creating a new object

There shouldn't be any LINQ magic keeping you from doing this. Don't use projection though that'll return an anonymous type.

User u = UserCollection.FirstOrDefault(u => u.Id == 1);
u.FirstName = "Bob"

That will modify the real object, as well as:

foreach (User u in UserCollection.Where(u => u.Id > 10)
    u.Property = SomeValue;

What is the use of the @ symbol in PHP?

It suppresses errors.

See Error Control Operators in the manual:

PHP supports one error control operator: the at sign (@). When prepended to an expression in PHP, any error messages that might be generated by that expression will be ignored.

If you have set a custom error handler function with set_error_handler() then it will still get called, but this custom error handler can (and should) call error_reporting() which will return 0 when the call that triggered the error was preceded by an @...

Check if year is leap year in javascript

A faster solution is provided by Kevin P. Rice here: So here's the code:

function leapYear(year)
    return (year & 3) == 0 && ((year % 25) != 0 || (year & 15) == 0);

Authentication failed for

After struggling with git authentication and azure devops server and trying other answers this tip here worked for me.

Using Visual Studio? Team Explorer handles authentication with Azure Repos for you.

Once I connected to the repo using Team Explorer I could use command line to execute git commands.

How to use Utilities.sleep() function

Serge is right - my workaround:

function mySleep (sec)

Correctly ignore all files recursively under a specific folder except for a specific file type

This might look stupid, but check if you haven't already added the folder/files you are trying to ignore to the index before. If you did, it does not matter what you put in your .gitignore file, the folders/files will still be staged.

Get file size before uploading

Please do not use ActiveX as chances are that it will display a scary warning message in Internet Explorer and scare your users away.

ActiveX warning

If anyone wants to implement this check, they should only rely on the FileList object available in modern browsers and rely on server side checks only for older browsers (progressive enhancement).

function getFileSize(fileInputElement){
    if (!fileInputElement.value ||
        typeof fileInputElement.files === 'undefined' ||
        typeof fileInputElement.files[0] === 'undefined' ||
        typeof fileInputElement.files[0].size !== 'number'
    ) {
        // File size is undefined.
        return undefined;

    return fileInputElement.files[0].size;

Convert List<T> to ObservableCollection<T> in WP7

The answer provided by Zin Min solved my problem with a single line of code. Excellent!

I was having the same issue of converting a generic List to a generic ObservableCollection to use the values from my List to populate a ComboBox that is participating in binding via a factory class for a WPF Window.

_expediteStatuses = new ObservableCollection<ExpediteStatus>(_db.getExpediteStatuses());

Here is the signature for the getExpediteStatuses method:

public List<ExpediteStatus> getExpediteStatuses()

What is the use of verbose in Keras while validating the model?

The order of details provided with verbose flag are as

Less details.... More details

0 < 2 < 1

Default is 1

For production environment, 2 is recommended

How to use boolean datatype in C?

C99 has a boolean datatype, actually, but if you must use older versions, just define a type:

typedef enum {false=0, true=1} bool;

How do I include a path to libraries in g++

In your MakeFile or CMakeLists.txt you can set CMAKE_CXX_FLAGS as below:

set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -I/path/to/your/folder")

SQL - Create view from multiple tables

This works too and you dont have to use join or anything:


    SELECT table1.column1, 
table1, table2 
WHERE table1.column1 = table2.column1;

Android center view in FrameLayout doesn't work

To center a view in Framelayout, there are some available tricks. The simplest one I used for my Webview and Progressbar(very similar to your two object layout), I just added android:layout_gravity="center"

Here is complete XML in case if someone else needs the same thing to do

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android=""




Here is my output


Matplotlib - How to plot a high resolution graph?

At the end of your for() loop, you can use the savefig() function instead of and set the name, dpi and format of your figure.

E.g. 1000 dpi and eps format are quite a good quality, and if you want to save every picture at folder ./ with names 'Sample1.eps', 'Sample2.eps', etc. you can just add the following code:

for fname in glob("./*.txt"):
    # Your previous code goes here

    plt.savefig("./{}.eps".format(fname), bbox_inches='tight', format='eps', dpi=1000)

ggplot2, change title size

+ theme(plot.title = element_text(size=22))

Here is the full set of things you can change in element_text:

element_text(family = NULL, face = NULL, colour = NULL, size = NULL,
  hjust = NULL, vjust = NULL, angle = NULL, lineheight = NULL,
  color = NULL)

Convert numpy array to tuple

I was not satisfied, so I finally used this:

>>> a=numpy.array([[1,2,3],[4,5,6]])
>>> a
array([[1, 2, 3],
       [4, 5, 6]])

>>> tuple(a.reshape(1, -1)[0])
(1, 2, 3, 4, 5, 6)

I don't know if it's quicker, but it looks more effective ;)

Finding all possible permutations of a given string in python

The itertools module has a useful method called permutations(). The documentation says:

itertools.permutations(iterable[, r])

Return successive r length permutations of elements in the iterable.

If r is not specified or is None, then r defaults to the length of the iterable and all possible full-length permutations are generated.

Permutations are emitted in lexicographic sort order. So, if the input iterable is sorted, the permutation tuples will be produced in sorted order.

You'll have to join your permuted letters as strings though.

>>> from itertools import permutations
>>> perms = [''.join(p) for p in permutations('stack')]
>>> perms

['stack', 'stakc', 'stcak', 'stcka', 'stkac', 'stkca', 'satck', 'satkc', 'sactk', 'sackt', 'saktc', 'sakct', 'sctak', 'sctka', 'scatk', 'scakt', 'sckta', 'sckat', 'sktac', 'sktca', 'skatc', 'skact', 'skcta', 'skcat', 'tsack', 'tsakc', 'tscak', 'tscka', 'tskac', 'tskca', 'tasck', 'taskc', 'tacsk', 'tacks', 'taksc', 'takcs', 'tcsak', 'tcska', 'tcask', 'tcaks', 'tcksa', 'tckas', 'tksac', 'tksca', 'tkasc', 'tkacs', 'tkcsa', 'tkcas', 'astck', 'astkc', 'asctk', 'asckt', 'asktc', 'askct', 'atsck', 'atskc', 'atcsk', 'atcks', 'atksc', 'atkcs', 'acstk', 'acskt', 'actsk', 'actks', 'ackst', 'ackts', 'akstc', 'aksct', 'aktsc', 'aktcs', 'akcst', 'akcts', 'cstak', 'cstka', 'csatk', 'csakt', 'cskta', 'cskat', 'ctsak', 'ctska', 'ctask', 'ctaks', 'ctksa', 'ctkas', 'castk', 'caskt', 'catsk', 'catks', 'cakst', 'cakts', 'cksta', 'cksat', 'cktsa', 'cktas', 'ckast', 'ckats', 'kstac', 'kstca', 'ksatc', 'ksact', 'kscta', 'kscat', 'ktsac', 'ktsca', 'ktasc', 'ktacs', 'ktcsa', 'ktcas', 'kastc', 'kasct', 'katsc', 'katcs', 'kacst', 'kacts', 'kcsta', 'kcsat', 'kctsa', 'kctas', 'kcast', 'kcats']

If you find yourself troubled by duplicates, try fitting your data into a structure with no duplicates like a set:

>>> perms = [''.join(p) for p in permutations('stacks')]
>>> len(perms)
>>> len(set(perms))

Thanks to @pst for pointing out that this is not what we'd traditionally think of as a type cast, but more of a call to the set() constructor.

fill an array in C#

public static void Fill<T>(this IList<T> col, T value, int fromIndex, int toIndex)
    if (fromIndex > toIndex)
        throw new ArgumentOutOfRangeException("fromIndex");

    for (var i = fromIndex; i <= toIndex; i++)
        col[i] = value;

Something that works for all IList<T>s.

How to keep a VMWare VM's clock in sync?

If your host time is correct, you can set the following .vmx configuration file option to enable periodic synchronization:

tools.syncTime = true

By default, this synchronizes the time every minute. To change the periodic rate, set the following option to the desired synch time in seconds:

tools.syncTime.period = 60

For this to work you need to have VMWare tools installed in your guest OS.

See for more information

Post order traversal of binary tree without recursion

This is what I've come up for post order iterator:

    class PostOrderIterator
    implements Iterator<T> {

        private Stack<Node<T>> stack;
        private Node<T> prev;

        PostOrderIterator(Node<T> root) {
            this.stack = new Stack<>();
            this.prev = this.stack.peek();

        private void recurse(Node<T> node) {
            if(node == null) {

            while(node != null) {
                node = node.left;

        public boolean hasNext() {
            return !stack.isEmpty();

        public T next() {
            if(stack.peek().right != this.prev) {

            Node<T> next = stack.pop();
            this.prev = next;
            return next.value;

Basically, the main idea is that you should think how the initialization process puts the first item to print on the top of the stack, while the rest of the stack follow the nodes that would have been touched by the recursion. The rest would just then become a lot easier to nail.

Also, from design perspective, PostOrderIterator is an internal class exposed via some factory method of the tree class as an Iterator<T>.

MySQL user DB does not have password columns - Installing MySQL on OSX

Use the ALTER USER command rather than trying to update a USER row. Keep in mind that there may be more than one 'root' user, because user entities are qualified also by the machine from which they connect

For example.

ALTER USER 'root'@'localhost' IDENTIFIED BY 'new-password' 
ALTER USER 'root'@'*' IDENTIFIED BY 'new-password' 

What is the difference between require() and library()?

You can use require() if you want to install packages if and only if necessary, such as:

if (!require(package, character.only=T, quietly=T)) {
    library(package, character.only=T)

For multiple packages you can use

for (package in c('<package1>', '<package2>')) {
    if (!require(package, character.only=T, quietly=T)) {
        library(package, character.only=T)

Pro tips:

  • When used inside the script, you can avoid a dialog screen by specifying the repos parameter of install.packages(), such as

    install.packages(package, repos="")
  • You can wrap require() and library() in suppressPackageStartupMessages() to, well, suppress package startup messages, and also use the parameters require(..., quietly=T, warn.conflicts=F) if needed to keep the installs quiet.

Less aggressive compilation with CSS3 calc

There's a tidier way to include variables inside the escaped calc, as explained in this post: CSS3 calc() function doesn't work with Less #974

@variable: 2em;

body{ width: calc(~"100% - @{variable} * 2");}

By using the curly brackets you don't need to close and reopen the escaping quotes.

Switching to a TabBar tab view programmatically?

I tried what Disco S2 suggested, it was close but this is what ended up working for me. This was called after completing an action inside another tab.

for (UINavigationController *controller in self.tabBarController.viewControllers)
    if ([controller isKindOfClass:[MyViewController class]])
        [self.tabBarController setSelectedViewController:controller];

How do I draw a set of vertical lines in gnuplot?

alternatively you can also do this:

p '< echo "x y"' w impulse

x and y are the coordinates of the point to which you draw a vertical bar

Iterating through list of list in Python

This can also be achieved with itertools.chain.from_iterable which will flatten the consecutive iterables:

import itertools
for item in itertools.chain.from_iterable(iterables):
    # do something with item    

T-test in Pandas

I simplify the code a little bit.

from scipy.stats import ttest_ind
ttest_ind(*my_data.groupby('Category')['value'].apply(lambda x:list(x)))

Common elements comparison between 2 lists

You can also use sets and get the commonalities in one line: subtract the set containing the differences from one of the sets.

A = [1,2,3,4]
B = [2,4,7,8]
commonalities = set(A) - (set(A) - set(B))

Check to see if cURL is installed locally?

Assuming you want curl installed: just execute the install command and see what happens.

$ sudo yum install curl

Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
 * base:
 * epel:
 * extras:
 * remi-php72:
 * remi-safe:
 * updates:
Package curl-7.29.0-54.el7_7.1.x86_64 already installed and latest version
Nothing to do

jquery multiple checkboxes array

A global function that can be reused:

function getCheckedGroupBoxes(groupName) {

    var checkedAry= [];
    $.each($("input[name='" + groupName + "']:checked"), function () {

     return checkedAry;


where the groupName is the name of the group of the checkboxes, in you example :'options[]'

Angular - res.json() is not a function

Don't need to use this method:

 .map((res: Response) => res.json() );

Just use this simple method instead of the previous method. hopefully you'll get your result:

.map(res => res );

Difference between a Seq and a List in Scala

In Java terms, Scala's Seq would be Java's List, and Scala's List would be Java's LinkedList.

Note that Seq is a trait, which is equivalent to Java's interface, but with the equivalent of up-and-coming defender methods. Scala's List is an abstract class that is extended by Nil and ::, which are the concrete implementations of List.

So, where Java's List is an interface, Scala's List is an implementation.

Beyond that, Scala's List is immutable, which is not the case of LinkedList. In fact, Java has no equivalent to immutable collections (the read only thing only guarantees the new object cannot be changed, but you still can change the old one, and, therefore, the "read only" one).

Scala's List is highly optimized by compiler and libraries, and it's a fundamental data type in functional programming. However, it has limitations and it's inadequate for parallel programming. These days, Vector is a better choice than List, but habit is hard to break.

Seq is a good generalization for sequences, so if you program to interfaces, you should use that. Note that there are actually three of them: collection.Seq, collection.mutable.Seq and collection.immutable.Seq, and it is the latter one that is the "default" imported into scope.

There's also GenSeq and ParSeq. The latter methods run in parallel where possible, while the former is parent to both Seq and ParSeq, being a suitable generalization for when parallelism of a code doesn't matter. They are both relatively newly introduced, so people doesn't use them much yet.

React.js create loop through Array

In CurrentGame component you need to change initial state because you are trying use loop for participants but this property is undefined that's why you get error.,

getInitialState: function(){
    return {
       data: {
          participants: [] 

also, as player in .map is Object you should get properties from it {
   return <li key={player.championId}>{player.summonerName}</li>
   // -------------------^^^^^^^^^^^---------^^^^^^^^^^^^^^


How can I get the baseurl of site?

I go with


How to set initial value and auto increment in MySQL?

First you need to add column for auto increment

alter table users add column id int(5) NOT NULL AUTO_INCREMENT FIRST

This query for add column at first. Now you have to reset auto increment initial value. So use this query

alter table users AUTO_INCREMENT=1001

Now your table started with 1001

How to add more than one machine to the trusted hosts list using winrm

winrm set winrm/config/client '@{TrustedHosts="machineA,machineB"}'

Simple way to find if two different lists contain exactly the same elements?

If you're using (or are happy to use) Apache Commons Collections, you can use CollectionUtils.isEqualCollection which "returns true iff the given Collections contain exactly the same elements with exactly the same cardinalities."

How do I run a VBScript in 32-bit mode on a 64-bit machine?

We can force vbscript always run with 32 bit mode by changing "system32" to "sysWOW64" in default value of key "Computer\HKLM\SOFTWARE]\Classes\VBSFile\Shell\Open\Command"

SQL Server Express 2008 Install Side-by-side w/ SQL 2005 Express Fails

Although you should have no problem running a 2005 instance of the database engine beside a 2008 instance, The tools are installed into a shared directory, so you can't have two versions of the tools installed. Fortunately, the 2008 tools are backwards-compatible. As we speak, I'm using SSMS 2008 and Profiler 2008 to manage my 2005 Express instances. Works great.

Before installing the 2008 tools, you need to remove any and all "shared" components from 2005. Try going to your Add/Remove programs control panel, find Microsoft SQL Server 2005, and click "Change." Then choose "Workstation Components" and remove everything there (this will not remove your database engine).

I believe the 2008 installer also has an option to upgrade shared components only. You might try that. Good luck!

What is the difference between NULL, '\0' and 0?

"NUL" is not 0, but refers to the ASCII NUL character. At least, that's how I've seen it used. The null pointer is often defined as 0, but this depends on the environment you are running in, and the specification of whatever operating system or language you are using.

In ANSI C, the null pointer is specified as the integer value 0. So any world where that's not true is not ANSI C compliant.

Dynamic tabs with user-click chosen components

there is component ready to use (rc5 compatible) ng2-steps which uses Compiler to inject component to step container and service for wiring everything together (data sync)

    import { Directive , Input, OnInit, Compiler , ViewContainerRef } from '@angular/core';

import { StepsService } from './ng2-steps';

export class StepDirective implements OnInit{

  @Input('content') content:any;
  @Input('index') index:string;
  public instance;

    private compiler:Compiler,
    private viewContainerRef:ViewContainerRef,
    private sds:StepsService

      const injector = this.viewContainerRef.injector;
      this.viewContainerRef.createComponent(cmpFactory, 0,  injector);


Escaping backslash in string - javascript

For security reasons, it is not possible to get the real, full path of a file, referred through an <input type="file" /> element.

This question already mentions, and links to other Stack Overflow questions regarding this topic.

Previous answer, kept as a reference for future visitors who reach this page through the title, tags and question.
The backslash has to be escaped.

string = string.split("\\");

In JavaScript, the backslash is used to escape special characters, such as newlines (\n). If you want to use a literal backslash, a double backslash has to be used.

So, if you want to match two backslashes, four backslashes has to be used. For example,alert("\\\\") will show a dialog containing two backslashes.

get basic SQL Server table structure information

For total columns information use below syntax : Use "DBName" go Exec SP_Columns "TableName"

For total table information use below syntax : Use "DBName" go Exec SP_help "Table Name"