Programs & Examples On #Dynamic values

Get filename from file pointer

You can get the path via Example:

>>> f = open('foo/bar.txt')

You might need os.path.basename if you want only the file name:

>>> import os
>>> f = open('foo/bar.txt')
>>> os.path.basename(

File object docs (for Python 2) here.

How does C#'s random number generator work?

You can use Random.Next(int maxValue):

Return: A 32-bit signed integer greater than or equal to zero, and less than maxValue; that is, the range of return values ordinarily includes zero but not maxValue. However, if maxValue equals zero, maxValue is returned.

var r = new Random();
// print random integer >= 0 and  < 100

For this case however you could use Random.Next(int minValue, int maxValue), like this:

// print random integer >= 1 and < 101
Console.WriteLine(r.Next(1, 101);)
// or perhaps (if you have this specific case)
Console.WriteLine(r.Next(100) + 1);

Max tcp/ip connections on Windows Server 2008

There is a limit on the number of half-open connections, but afaik not for active connections. Although it appears to depend on the type of Windows 2008 server, at least according to this MSFT employee:

It depends on the edition, Web and Foundation editions have connection limits while Standard, Enterprise, and Datacenter do not.

Git - Won't add files?

I am still a beginner at git, and it was just a stupid mistake I made, long story in one sentence. I was not in a subfolder as @gaoagong reported, but the other way round, in a parent folder. Strange enough, I did not get the idea from that answer, instead, the idea came up when I tested git add --all, see the long story below.

Example in details. Actual repo:

enter image description here

The Parent folder that I had opened mistakenly on parent level (vscode_git in my case):

enter image description here

I had cloned a repo, but I had a parent folder above this repo which I had opened instead, and then I tried adding a file of the subfolder's repo with git add 'd:\Stack Overflow\vscode_git\vscode-java\.github\', which simply did nothing, no warning message, and the git status afterwards said:

nothing added to commit but untracked files present (use "git add" to track)

enter image description here

Running git add --all gave me the yellow notes:

warning: adding embedded git repository: vscode-java the embedded repository and will not know how to obtain it.

hint: If you meant to add a submodule, use: git submodule add vscode-java

hint: If you added this path by mistake, you can remove it from the index with git rm --cached vscode-java

See "git help submodule" for more information.git

enter image description here

To fix this, I reverted the git add --all with git rm --cached -r -f -- "d:\Stack Overflow\vscode_git\vscode-java" rm 'vscode-java':

enter image description here

Then, by simply opening the actual repo folder instead,

enter image description here

the git worked as expected again. Of course the ".git" folder of the parent folder could be deleted then:

enter image description here

Control the dashed border stroke length and distance between strokes

Stroke length depends on stroke width. You can increase length by increasing width and hide part of border by inner element.

EDIT: added pointer-events: none; thanks to benJ.

.thin {
    background: #F4FFF3;
    border: 2px dashed #3FA535;  
    position: relative;

.thin:after {
    content: '';
    position: absolute;
    left: -1px;
    top: -1px;
    right: -1px;
    bottom: -1px;
    border: 1px solid #F4FFF3;
    pointer-events: none;

How to compare two dates along with time in java

Since Date implements Comparable<Date>, it is as easy as:


As the Comparable contract stipulates, it will return a negative integer/zero/positive integer if date1 is considered less than/the same as/greater than date2 respectively (ie, before/same/after in this case).

Note that Date has also .after() and .before() methods which will return booleans instead.

center a row using Bootstrap 3

Why not using the grid system?

The bootstrap grid system consist of 12 columns, so if you use the "Medium" columns it will have a 970px width size.

Then you can divide it to 3 columns (12/3=4) so use 3 divs with "col-md-4" class:

<div class="col-md-4"></div>
<div class="col-md-4"></div>
<div class="col-md-4"></div>

Each one will have 323px max width size. Keep the first and the last empty and use the middle one to get your content centerd:

<div class="col-md-4"></div>
<div class="col-md-4">
   <p>Centered content.</p>
<div class="col-md-4"></div>

docker: executable file not found in $PATH

When you use the exec format for a command (e.g. CMD ["grunt"], a JSON array with double quotes) it will be executed without a shell. This means that most environment variables will not be present.

If you specify your command as a regular string (e.g. CMD grunt) then the string after CMD will be executed with /bin/sh -c.

More info on this is available in the CMD section of the Dockerfile reference.

How can I generate a list of files with their absolute path in Linux?

You can do

ls -1 |xargs realpath

If you need to specify an absolute path or relative path You can do that as well

 ls -1 $FILEPATH |xargs realpath

Distribution certificate / private key not installed

In my case Xcode was not accessing certificates from the keychain, I followed these steps:

  1. delete certificates from the keychain.
  2. restart the mac.
  3. generate new certificates.
  4. install new certificates.
  5. clean build folder.
  6. build project.
  7. again clean build folder.
  8. archive now. It works That's it.

How to create a file name with the current date & time in Python?

This one is much more human readable.

from datetime import datetime"%Y_%m_%d-%I_%M_%S_%p")

How to write unit testing for Angular / TypeScript for private methods with Jasmine

I'm with you, even though it's a good goal to "only unit test the public API" there are times when it doesn't seem that simple and you feel you are choosing between compromising either the API or the unit-tests. You know this already, since that's exactly what you're asking to do, so I won't get into it. :)

In TypeScript I've discovered a few ways you can access private members for the sake of unit-testing. Consider this class:

class MyThing {

    private _name:string;
    private _count:number;

    constructor() {
        this.init("Test", 123);

    private init(name:string, count:number){
        this._name = name;
        this._count = count;

    public get name(){ return this._name; }

    public get count(){ return this._count; }


Even though TS restricts access to class members using private, protected, public, the compiled JS has no private members, since this isn't a thing in JS. It's purely used for the TS compiler. Therefor:

  1. You can assert to any and escape the compiler from warning you about access restrictions:

    (thing as any)._name = "Unit Test";
    (thing as any)._count = 123;
    (thing as any).init("Unit Test", 123);

    The problem with this approach is that the compiler simply has no idea what you are doing right of the any, so you don't get desired type errors:

    (thing as any)._name = 123; // wrong, but no error
    (thing as any)._count = "Unit Test"; // wrong, but no error
    (thing as any).init(0, "123"); // wrong, but no error

    This will obviously make refactoring more difficult.

  2. You can use array access ([]) to get at the private members:

    thing["_name"] = "Unit Test";
    thing["_count"] = 123;
    thing["init"]("Unit Test", 123);

    While it looks funky, TSC will actually validate the types as if you accessed them directly:

    thing["_name"] = 123; // type error
    thing["_count"] = "Unit Test"; // type error
    thing["init"](0, "123"); // argument error

    To be honest I don't know why this works. This is apparently an intentional "escape hatch" to give you access to private members without losing type safety. This is exactly what I think you want for your unit-testing.

Here is a working example in the TypeScript Playground.

Edit for TypeScript 2.6

Another option that some like is to use // @ts-ignore (added in TS 2.6) which simply suppresses all errors on the following line:

// @ts-ignore
thing._name = "Unit Test";

The problem with this is, well, it suppresses all errors on the following line:

// @ts-ignore
thing._name(123).this.should.NOT.beAllowed("but it is") = window / {};

I personally consider @ts-ignore a code-smell, and as the docs say:

we recommend you use this comments very sparingly. [emphasis original]

MySQL Select Query - Get only first 10 characters of a value

Have a look at either Left or Substring if you need to chop it up even more.

Google and the MySQL docs are a good place to start - you'll usually not get such a warm response if you've not even tried to help yourself before asking a question.

Get value when selected ng-option changes

You will get selected option's value and text from list/array by using filter.

<select name="statusSelect"
      ng-options="option.Value as option.KeyName for option in EmployeeStatus"

PHP random string generator

This creates a 20 character long hexadecimal string:

$string = bin2hex(openssl_random_pseudo_bytes(10)); // 20 chars

In PHP 7 (random_bytes()):

$string = base64_encode(random_bytes(10)); // ~14 characters, includes /=+
// or
$string = substr(str_replace(['+', '/', '='], '', base64_encode(random_bytes(32))), 0, 32); // 32 characters, without /=+
// or
$string = bin2hex(random_bytes(10)); // 20 characters, only 0-9a-f

PHP move_uploaded_file() error?

Please check that your form tag have this attribute:


Android - Handle "Enter" in an EditText

This will give you a callable function when the user presses the return key.

fun EditText.setLineBreakListener(onLineBreak: () -> Unit) {
    val lineBreak = "\n"
    doOnTextChanged { text, _, _, _ ->
        val currentText = text.toString()

        // Check if text contains a line break
        if (currentText.contains(lineBreak)) {

            // Uncommenting the lines below will remove the line break from the string
            // and set the cursor back to the end of the line

            // val cleanedString = currentText.replace(lineBreak, "")
            // setText(cleanedString)
            // setSelection(cleanedString.length)



editText.setLineBreakListener {

Shared folder between MacOSX and Windows on Virtual Box

You should map your virtual network drive in Windows.

  1. Open command prompt in Windows (VirtualBox)
  2. Execute: net use x: \\vboxsvr\<your_shared_folder_name>
  3. You should see new drive X: in My Computer

In your case execute net use x: \\vboxsvr\win7

Parsing JSON array with PHP foreach

You maybe wanted to do the following:

foreach($user->data as $mydata)

         echo $mydata->name . "\n";
         foreach($mydata->values as $values)
              echo $values->value . "\n";

Can I use an HTML input type "date" to collect only a year?

No, you can't, it doesn't support only year, so to do that you need a script, like jQuery or the webshim link you have, which shows year only.

If jQuery would be an option, here is one, borrowed from Sibu:


$(function() {
    $( "#datepicker" ).datepicker({dateFormat: 'yy'});


.ui-datepicker-calendar {
   display: none;


Src fiddle:

Here is an updated fiddle, without the month and prev/next buttons

If bootstrap is an option, check this link, they have a layout how you want.

Connecting client to server using

You need to make sure that you add forward slash before your link to

<script src="/"></script>

Then in the view/controller just do:

var socket = io.connect()

That should solve your problem.

Android: Cancel Async Task

FOUND THE SOLUTION: I added an action listener before like this:

    uploadingDialog.setOnCancelListener(new DialogInterface.OnCancelListener(){
          public void onCancel(DialogInterface dialog) {

That way when I press the back button, the above OnCancelListener cancels both dialog and task. Also you can add finish() if you want to finish the whole activity on back pressed. Remember to declare your async task as a variable like this:

    MyAsyncTask myTask=null;

and execute your async task like this:

    myTask = new MyAsyncTask();

How to change the port number for Asp.Net core app?

Use following one line of code .UseUrls("http://*:80") in Program.cs

Thus changing .UseStartup<Startup>()


.UseStartup<Startup>() .UseUrls("http://*:80")

How to initialize a struct in accordance with C programming language standards

In (ANSI) C99, you can use a designated initializer to initialize a structure:

MY_TYPE a = { .flag = true, .value = 123, .stuff = 0.456 };

Edit: Other members are initialized as zero: "Omitted field members are implicitly initialized the same as objects that have static storage duration." (

Expression must have class type

Summary: Instead of a.f(); it should be a->f();

In main you have defined a as a pointer to object of A, so you can access functions using the -> operator.

An alternate, but less readable way is (*a).f()

a.f() could have been used to access f(), if a was declared as: A a;

Returning a file to View/Download in ASP.NET MVC

To view file (txt for example):

return File("~/TextFileInRootDir.txt", MediaTypeNames.Text.Plain);

To download file (txt for example):

return File("~/TextFileInRootDir.txt", MediaTypeNames.Text.Plain, "TextFile.txt");

note: to download file we should pass fileDownloadName argument

How to configure PHP to send e-mail?

You won't be able to send a message through other people mail servers. Check with your host provider how to send emails. Try to send an email from your server without PHP, you can use any email client like Outook. Just after it works, try to configure PHP.ini with your email client SMTP (sending e-mail) configuration.

CSS Flex Box Layout: full-width row and columns

Just use another container to wrap last two divs. Don't forget to use CSS prefixes.

#productShowcaseContainer {_x000D_
   display: flex;_x000D_
   flex-direction: column;_x000D_
   height: 600px;_x000D_
   width: 580px;_x000D_
   background-color: rgb(240, 240, 240);_x000D_
#productShowcaseTitle {_x000D_
   height: 100px;_x000D_
   background-color: rgb(200, 200, 200);_x000D_
   display: flex;_x000D_
   height: 100%;_x000D_
#productShowcaseDetail {_x000D_
   background-color: red;_x000D_
   flex: 4;_x000D_
#productShowcaseThumbnailContainer {_x000D_
   background-color: blue;_x000D_
   flex: 1;_x000D_
<div id="productShowcaseContainer">_x000D_
   <div id="productShowcaseTitle">1</div>_x000D_
   <div id="anotherContainer">_x000D_
      <div id="productShowcaseDetail">2</div>_x000D_
      <div id="productShowcaseThumbnailContainer">3</div>_x000D_

C++ Returning reference to local variable

This code snippet:

int& func1()
    int i;
    i = 1;
    return i;

will not work because you're returning an alias (a reference) to an object with a lifetime limited to the scope of the function call. That means once func1() returns, int i dies, making the reference returned from the function worthless because it now refers to an object that doesn't exist.

int main()
    int& p = func1();
    /* p is garbage */

The second version does work because the variable is allocated on the free store, which is not bound to the lifetime of the function call. However, you are responsible for deleteing the allocated int.

int* func2()
    int* p;
    p = new int;
    *p = 1;
    return p;

int main()
    int* p = func2();
    /* pointee still exists */
    delete p; // get rid of it

Typically you would wrap the pointer in some RAII class and/or a factory function so you don't have to delete it yourself.

In either case, you can just return the value itself (although I realize the example you provided was probably contrived):

int func3()
    return 1;

int main()
    int v = func3();
    // do whatever you want with the returned value

Note that it's perfectly fine to return big objects the same way func3() returns primitive values because just about every compiler nowadays implements some form of return value optimization:

class big_object 
    big_object(/* constructor arguments */);
    big_object(const big_object& rhs);
    big_object& operator=(const big_object& rhs);
    /* public methods */
    /* data members */

big_object func4()
    return big_object(/* constructor arguments */);

int main()
     // no copy is actually made, if your compiler supports RVO
    big_object o = func4();    

Interestingly, binding a temporary to a const reference is perfectly legal C++.

int main()
    // This works! The returned temporary will last as long as the reference exists
    const big_object& o = func4();    
    // This does *not* work! It's not legal C++ because reference is not const.
    // big_object& o = func4();  

Eclipse copy/paste entire line keyboard shortcut

I am using Windows 7. To disable that all I did is to Right click on the Windows desktop and select "Graphics Properties" ->Options. Then selected "Off" at the left side on the resulting screen. This disabled all hotkey combination. I think there is no way to disable only some them, its all or none. Anyway I didn't need them. So now crtl+Alt+Up and Crtl+Alt+down works for me in Eclipse and my screen stays same :) I think similar option also exist in other versions of Windows. Have fun :)

Using OR in SQLAlchemy

SQLAlchemy overloads the bitwise operators &, | and ~ so instead of the ugly and hard-to-read prefix syntax with or_() and and_() (like in Bastien's answer) you can use these operators:

.filter((AddressBook.lastname == 'bulger') | (AddressBook.firstname == 'whitey'))

Note that the parentheses are not optional due to the precedence of the bitwise operators.

So your whole query could look like this:

addr = session.query(AddressBook) \
    .filter( == "boston") \
    .filter((AddressBook.lastname == 'bulger') | (AddressBook.firstname == 'whitey'))

how to query child objects in mongodb

If it is exactly null (as opposed to not set):

db.states.find({"": null})

(but as javierfp points out, it also matches documents that have no cities array at all, I'm assuming that they do).

If it's the case that the property is not set:

db.states.find({"": {"$exists": false}})

I've tested the above with a collection created with these two inserts:

db.states.insert({"cities": [{name: "New York"}, {name: null}]})
db.states.insert({"cities": [{name: "Austin"}, {color: "blue"}]})

The first query finds the first state, the second query finds the second. If you want to find them both with one query you can make an $or query:

db.states.find({"$or": [
  {"": null}, 
  {"": {"$exists": false}}

Favicon not showing up in Google Chrome

Upload your favicon.ico to the root directory of your website and that should work with Chrome. Some browsers disregard the meta tag and just use /favicon.ico

Go figure?.....

Convert JS object to JSON string

All current browsers have native JSON support built in. So as long as you're not dealing with prehistoric browsers like IE6/7 you can do it just as easily as that:

var j = {_x000D_
  "name": "binchen"_x000D_

Can dplyr package be used for conditional mutating?

Since you ask for other better ways to handle the problem, here's another way using data.table:

require(data.table) ## 1.9.2+
df[a %in% c(0,1,3,4) | c == 4, g := 3L]
df[a %in% c(2,5,7) | (a==1 & b==4), g := 2L]

Note the order of conditional statements is reversed to get g correctly. There's no copy of g made, even during the second assignment - it's replaced in-place.

On larger data this would have better performance than using nested if-else, as it can evaluate both 'yes' and 'no' cases, and nesting can get harder to read/maintain IMHO.

Here's a benchmark on relatively bigger data:

# R version 3.1.0
require(data.table) ## 1.9.2
DT <- setDT(lapply(1:6, function(x) sample(7, 1e7, TRUE)))
setnames(DT, letters[1:6])
# > dim(DT) 
# [1] 10000000        6
DF <-

DT_fun <- function(DT) {
    DT[(a %in% c(0,1,3,4) | c == 4), g := 3L]
    DT[a %in% c(2,5,7) | (a==1 & b==4), g := 2L]

DPLYR_fun <- function(DF) {
    mutate(DF, g = ifelse(a %in% c(2,5,7) | (a==1 & b==4), 2L, 
            ifelse(a %in% c(0,1,3,4) | c==4, 3L, NA_integer_)))

BASE_fun <- function(DF) { # R v3.1.0
    transform(DF, g = ifelse(a %in% c(2,5,7) | (a==1 & b==4), 2L, 
            ifelse(a %in% c(0,1,3,4) | c==4, 3L, NA_integer_)))

system.time(ans1 <- DT_fun(DT))
#   user  system elapsed 
#  2.659   0.420   3.107 

system.time(ans2 <- DPLYR_fun(DF))
#   user  system elapsed 
# 11.822   1.075  12.976 

system.time(ans3 <- BASE_fun(DF))
#   user  system elapsed 
# 11.676   1.530  13.319 

# [1] TRUE

# [1] TRUE

Not sure if this is an alternative you'd asked for, but I hope it helps.

Multiple REPLACE function in Oracle

This is an old post, but I ended up using Peter Lang's thoughts, and did a similar, but yet different approach. Here is what I did:

                        pString IN VARCHAR2
                        ,pReplacePattern IN VARCHAR2
    iCount  INTEGER;
    vResult VARCHAR2(1000);
    vRule   VARCHAR2(100);
    vOldStr VARCHAR2(50);
    vNewStr VARCHAR2(50);
    iCount := 0;
    vResult := pString;
        iCount := iCount + 1;

        -- Step # 1: Pick out the replacement rules
        vRule := REGEXP_SUBSTR(pReplacePattern, '[^/]+', 1, iCount);

        -- Step # 2: Pick out the old and new string from the rule
        vOldStr := REGEXP_SUBSTR(vRule, '[^=]+', 1, 1);
        vNewStr := REGEXP_SUBSTR(vRule, '[^=]+', 1, 2);

        -- Step # 3: Do the replacement
        vResult := REPLACE(vResult, vOldStr, vNewStr);

        EXIT WHEN vRule IS NULL;

    RETURN vResult;
END multi_replace;

Then I can use it like this:

SELECT  multi_replace(
                        'This is a test string with a #, a $ character, and finally a & character'
FROM dual

This makes it so that I can can any character/string with any character/string.

I wrote a post about this on my blog.

Eclipse: Set maximum line length for auto formatting?

In preferences Java -> Code Style -> Formatter, edit the profile. Under the Line Wrapping tab is the primary option for line width (Maximum line width:). In the Comments tab you have a separate option Maximum line width for comments:, which will also need to be changed to affect comment wrapping.

You will need to make your own profile to make these changes in if you using one of the [Built-in] ones. Just click "New..." on the formatter preferences page.

javac: invalid target release: 1.8

If this error occurs when running a Gradle (or Maven) task, you need to modify that build tool configuration to point to your installation of Java JDK 1.8 following this route:

File -> Settings -> Build, Execution, Deployment -> Build Tools -> Gradle

There you check the Linked Gradle project is the one you are working on and select the Gradle JVM (You missed this when you imported the gradle project into IntelliJ)

enter image description here

Remember when importing a Gradle (or Maven) project to set the target JVM correctly here: enter image description here

How do you monitor network traffic on the iPhone?

The best solution I have found that Works:

Connect your device thru USB

And type these commands:

  1. rvictl -s UDID - (id of device 20 chars, you can locate 4t in iTunes or organiser in Xcode)

  2. sudo launchctl list

  3. sudo tcpdump -n -t -i rvi0 -q tcp
    OR just sudo tcpdump -i rvi0 -n

If rvictl is not working install Xcode

For more info: Remote Virtual Interface

error: could not create '/usr/local/lib/python2.7/dist-packages/virtualenv_support': Permission denied

In the case of permission denied error, you just need to go with this command.

sudo pip install virtualenv

sudo before the command will throw away the current user permissions error.

Note: For security risks, You should read piotr comment.

OR operator in switch-case?

What are the backgrounds for a switch-case to not accept this operator?

Because case requires constant expression as its value. And since an || expression is not a compile time constant, it is not allowed.

From JLS Section 14.11:

Switch label should have following syntax:

case ConstantExpression :
case EnumConstantName :
default :

Under the hood:

The reason behind allowing just constant expression with cases can be understood from the JVM Spec Section 3.10 - Compiling Switches:

Compilation of switch statements uses the tableswitch and lookupswitch instructions. The tableswitch instruction is used when the cases of the switch can be efficiently represented as indices into a table of target offsets. The default target of the switch is used if the value of the expression of the switch falls outside the range of valid indices.

So, for the cases label to be used by tableswitch as a index into the table of target offsets, the value of the case should be known at compile time. That is only possible if the case value is a constant expression. And || expression will be evaluated at runtime, and the value will only be available at that time.

From the same JVM section, the following switch-case:

switch (i) {
    case 0:  return  0;
    case 1:  return  1;
    case 2:  return  2;
    default: return -1;

is compiled to:

0   iload_1             // Push local variable 1 (argument i)
1   tableswitch 0 to 2: // Valid indices are 0 through 2  (NOTICE This instruction?)
      0: 28             // If i is 0, continue at 28
      1: 30             // If i is 1, continue at 30
      2: 32             // If i is 2, continue at 32
      default:34        // Otherwise, continue at 34
28  iconst_0            // i was 0; push int constant 0...
29  ireturn             // ...and return it
30  iconst_1            // i was 1; push int constant 1...
31  ireturn             // ...and return it
32  iconst_2            // i was 2; push int constant 2...
33  ireturn             // ...and return it
34  iconst_m1           // otherwise push int constant -1...
35  ireturn             // ...and return it

So, if the case value is not a constant expressions, compiler won't be able to index it into the table of instruction pointers, using tableswitch instruction.

Checking whether the pip is installed?

If you are on a linux machine running Python 2 you can run this commands:

1st make sure python 2 is installed:

python2 --version

2nd check to see if pip is installed:

pip --version

If you are running Python 3 you can run this command:

1st make sure python 3 is installed:

python3 --version

2nd check to see if pip3 is installed:

pip3 --version

If you do not have pip installed you can run these commands to install pip (it is recommended you install pip for Python 2 and Python 3):

Install pip for Python 2:

sudo apt install python-pip

Then verify if it is installed correctly:

pip --version

Install pip for Python 3:

sudo apt install python3-pip

Then verify if it is installed correctly:

pip3 --version

For more info see:

UPDATE I would like to mention a few things. When working with Django I learned that my Linux install requires me to use python 2.7, so switching my default python version for the python and pip command alias's to python 3 with alias python=python3 is not recommended. Therefore I use the python3 and pip3 commands when installing software like Django 3.0, which works better with Python 3. And I keep their alias's pointed towards whatever Python 3 version I want like so alias python3=python3.8.

Keep In Mind When you are going to use your package in the future you will want to use the pip or pip3 command depending on which one you used to initially install the package. So for example if I wanted to change my change my Django package version I would use the pip3 command and not pip like so, pip3 install Django==3.0.11.

Notice When running checking the packages version for python: $ python -m django --version and python3: $ python3 -m django --version, two different versions of django will show because I installed django v3.0.11 with pip3 and django v1.11.29 with pip.

How to set the timezone in Django?

  1. Change the TIME_ZONE to your local time zone, and keep USE_TZ as True in '':

    TIME_ZONE = 'Asia/Shanghai'

    USE_I18N = True

    USE_L10N = True

    USE_TZ = True

  2. This will write and store the datetime object as UTC to the backend database.

  3. Then use template tag to convert the UTC time in your frontend template as such:

                    {% load tz %}
                    {% get_current_timezone as tz %}
                    {% timezone tz %}
                        {{ message.log_date | time:'H:i:s' }}
                    {% endtimezone %} 

or use the template filters concisely:

                    {% load tz %}
                    {{ message.log_date | localtime | time:'H:i:s' }}
  1. You could check more details in the official doc: Default time zone and current time zone

    When support for time zones is enabled, Django stores datetime information in UTC in the database, uses time-zone-aware datetime objects internally, and translates them to the end user’s time zone in templates and forms.

Rendering an in React

I've come cross an issue with the implementation of this solution.

If you have a custom component you want to iterate through and you want to share the state it will not be available as the .map() scope does not recognize the general state() scope. I've come to this solution:


class RootComponent extends Component() {
    constructor(props) {
        this.state = {thisWorks: false}
        this.that = this;
    componentDidMount() {
    render() {
       let array = => { 
           <CustomComponent that={this.that} customFunction={this.customFunction}/>

    customFunction() {
        this.that.setState({thisWorks: true})

class CustomComponent extend Component {

    render() {
        return <Button onClick={() => {this.props.customFunction()}}

In constructor bind without this.that Every use of any function/method inside the root component should be used with this.that

How to use vagrant in a proxy environment?

On windows, you must set a variable to specify proxy settings, download the vagrant-proxyconf plugin: (replace {PROXY_SCHEME}(http:// or https://), {PROXY_IP} and {PROXY_PORT} by the right values)


After that, you can add the plugin to hardcode your proxy settings in the vagrant file

vagrant plugin install vagrant-proxyconf --plugin-source

and then you can provide settings in your Vagrantfile to be independent against environment settings variables

How can I undo a mysql statement that I just executed?

in case you do not only need to undo your last query (although your question actually only points on that, I know) and therefore if a transaction might not help you out, you need to implement a workaround for this:

copy the original data before commiting your query and write it back on demand based on the unique id that must be the same in both tables; your rollback-table (with the copies of the unchanged data) and your actual table (containing the data that should be "undone" than). for databases having many tables, one single "rollback-table" containing structured dumps/copies of the original data would be better to use then one for each actual table. it would contain the name of the actual table, the unique id of the row, and in a third field the content in any desired format that represents the data structure and values clearly (e.g. XML). based on the first two fields this third one would be parsed and written back to the actual table. a fourth field with a timestamp would help cleaning up this rollback-table.

since there is no real undo in SQL-dialects despite "rollback" in a transaction (please correct me if I'm wrong - maybe there now is one), this is the only way, I guess, and you have to write the code for it on your own.

Importing Pandas gives error AttributeError: module 'pandas' has no attribute 'core' in iPython Notebook

You are getting this is because you are using a Anaconda distribution of Jupyter notebook. So just do conda install pandas restart your jupyter notebook and rerun your cell. It should work. If you are trying this on a Virtual Env try this

  1. conda create -n name_of_my_env python This will create a minimal environment with only Python installed in it. To put your self inside this environment run:

2 source activate name_of_my_env On Windows the command is: activate name_of_my_env The final step required is to install pandas. This can be done with the following command:

conda install pandas To install a specific pandas version:

conda install pandas=0.20.3

To install other packages, IPython for example:

conda install ipython To install the full Anaconda distribution:

conda install anaconda

If you need packages that are available to pip but not conda, then install pip, and then use pip to install those packages:

conda install pip pip install django Installing from PyPI pandas can be installed via pip from PyPI.

pip install pandas Installing with ActivePython

Hope this helps.

Can I use wget to check , but not download

If you want to check quietly via $? without the hassle of grep'ing wget's output you can use:

wget -q "" -O /dev/null

Works even on URLs with just a path but has the disadvantage that something's really downloaded so this is not recommended when checking big files for existence.

gulp command not found - error after installing gulp

I am using Windows 8.1. I had the same problem.

I installed gulp using Node.js command prompt

npm install -g gulp

Then go to the required directory in Node.js command prompt and try

gulp -v

If you get gulp local version not found exit the current Node.js command prompt and try the above command in a new Node.js command prompt

I tried the NODE_PATH mentioned by @SteveLacy but the command prompt was still not able to detect gulp command

Why does find -exec mv {} ./target/ + not work?

find . -name "*.mp3" -exec mv --target-directory=/home/d0k/??????/ {} \+

What’s the best way to get an HTTP response code from a URL?

Here's a solution that uses httplib instead.

import httplib

def get_status_code(host, path="/"):
    """ This function retreives the status code of a website by requesting
        HEAD data from the host. This means that it only requests the headers.
        If the host cannot be reached or something else goes wrong, it returns
        None instead.
        conn = httplib.HTTPConnection(host)
        conn.request("HEAD", path)
        return conn.getresponse().status
    except StandardError:
        return None

print get_status_code("") # prints 200
print get_status_code("", "/nonexistant") # prints 404

JS map return object

If you want to alter the original objects, then a simple Array#forEach will do:

rockets.forEach(function(rocket) {
    rocket.launches += 10;

If you want to keep the original objects unaltered, then use Array#map and copy the objects using Object#assign:

var newRockets = rockets.forEach(function(rocket) {
    var newRocket = Object.assign({}, rocket);
    newRocket.launches += 10;
    return newRocket;

How to join multiple collections with $lookup in mongodb

First add the collections and then apply lookup on these collections. Don't use $unwind as unwind will simply separate all the documents of each collections. So apply simple lookup and then use $project for projection. Here is mongoDB query:

        $lookup: {
           from: "userRole",
           localField: "userId",
           foreignField: "userId",
           as: "userRole"
        $lookup: {
            from: "userInfo",
            localField: "userId",
            foreignField: "userId",
            as: "userInfo"
    {$project: {
        } ])

Here is the output:

/* 1 */ {
    "userId" : "AD",
    "phone" : "0000000000",
    "userRole" : [ 
            "userId" : "AD",
            "role" : "admin"
    "userInfo" : [ 
            "userId" : "AD",
            "phone" : "0000000000"
    ] }


Can't subtract offset-naive and offset-aware datetimes

I also faced the same problem. Then I found a solution after a lot of searching .

The problem was that when we get the datetime object from model or form it is offset aware and if we get the time by system it is offset naive.

So what I did is I got the current time using and import the timezone by from django.utils import timezone and put the USE_TZ = True in your project settings file.

How do getters and setters work?

Tutorial is not really required for this. Read up on encapsulation

private String myField; //"private" means access to this is restricted

public String getMyField()
     //include validation, logic, logging or whatever you like here
    return this.myField;
public void setMyField(String value)
     //include more logic
     this.myField = value;

PLS-00428: an INTO clause is expected in this SELECT statement

In PLSQL block, columns of select statements must be assigned to variables, which is not the case in SQL statements.

The second BEGIN's SQL statement doesn't have INTO clause and that caused the error.

   DSC           VARCHAR (512);
    WHERE PART_NUM = 'S0146404';

             || ','
             || RTRIM (PLANID.DESC_TEXT)
             || ','
             || CASE
                   WHEN PLANID.HIGH = 'TEST123'
                         WHEN TO_DATE (PROD.START_DATE) + 30 > SYSDATE
             || ','
             || 'GB'
             || ','
        INTO DSC
                ON PROD.PART_NUM = PLANID.VAL
                ON PROD.PROD_ID = PROD.ROW_ID
                ON VIS.PROD_ID = VISPROD.ROW_ID
       WHERE     PLANID.TYPE = 'Test Plan'
             AND PLANID.ACTIVE_FLG = 'Y'
             AND PROD.STATUS_CD = 'Active'


How can I convert an image into Base64 string using JavaScript?

There are multiple approaches you can choose from:

1. Approach: FileReader

Load the image as blob via XMLHttpRequest and use the FileReader API (readAsDataURL()) to convert it to a dataURL:

function toDataURL(url, callback) {
  var xhr = new XMLHttpRequest();
  xhr.onload = function() {
    var reader = new FileReader();
    reader.onloadend = function() {
  };'GET', url);
  xhr.responseType = 'blob';

toDataURL('', function(dataUrl) {
  console.log('RESULT:', dataUrl)

This code example could also be implemented using the WHATWG fetch API:

const toDataURL = url => fetch(url)
  .then(response => response.blob())
  .then(blob => new Promise((resolve, reject) => {
    const reader = new FileReader()
    reader.onloadend = () => resolve(reader.result)
    reader.onerror = reject

  .then(dataUrl => {
    console.log('RESULT:', dataUrl)

These approaches:

  • lack in browser support
  • have better compression
  • work for other file types as well

Browser Support:

2. Approach: Canvas

Load the image into an Image-Object, paint it to a nontainted canvas and convert the canvas back to a dataURL.

function toDataURL(src, callback, outputFormat) {
  var img = new Image();
  img.crossOrigin = 'Anonymous';
  img.onload = function() {
    var canvas = document.createElement('CANVAS');
    var ctx = canvas.getContext('2d');
    var dataURL;
    canvas.height = this.naturalHeight;
    canvas.width = this.naturalWidth;
    ctx.drawImage(this, 0, 0);
    dataURL = canvas.toDataURL(outputFormat);
  img.src = src;
  if (img.complete || img.complete === undefined) {
    img.src = "data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///ywAAAAAAQABAAACAUwAOw==";
    img.src = src;

  function(dataUrl) {
    console.log('RESULT:', dataUrl)

In detail

Supported input formats:

image/png, image/jpeg, image/jpg, image/gif, image/bmp, image/tiff, image/x-icon, image/svg+xml, image/webp, image/xxx

Supported output formats:

image/png, image/jpeg, image/webp(chrome)

Browser Support:

3. Approach: Images from the local file system

If you want to convert images from the users file system you need to take a different approach. Use the FileReader API:

function encodeImageFileAsURL(element) {
  var file = element.files[0];
  var reader = new FileReader();
  reader.onloadend = function() {
    console.log('RESULT', reader.result)
<input type="file" onchange="encodeImageFileAsURL(this)" />

IIS - can't access page by ip address instead of localhost

I was trying to access my web pages on specific port number and tried much things, but I've found the port was filtered by firewall. Just added a bypass rule and everything was done.

Maybe help someone!

PivotTable's Report Filter using "greater than"

After some research I finally got a VBA code to show the filter value in another cell:

Dim bRepresentAsRange As Boolean, bRangeBroken As Boolean
Dim sSelection As String
Dim tbl As Variant
bRepresentAsRange = False
bRangeBroker = False

With Worksheets("Forecast").PivotTables("ForecastbyDivision")
            ReDim tbl(.PageFields("Probability").PivotItems.Count)
            For Each fld In .PivotFields("Probability").PivotItems

                If fld.Visible Then
                    tbl(n) = fld.Name
                    sSelection = sSelection & fld.Name & ","
                    n = n + 1
                    bRepresentAsRange = True
                    If bRepresentAsRange Then
                        bRepresentAsRange = False
                        bRangeBroken = True
                    End If
                End If

            Next fld

            If Not bRangeBroken Then
                Worksheets("Forecast").Range("ProbSelection") = " >= " & tbl(0)
                Worksheets("Forecast").Range("ProbSelection") = Left(sSelection, Len(sSelection) - 1)
            End If

        End With

nodejs module.js:340 error: cannot find module

Easy way for this problem

npm link e

TSQL - Cast string to integer or return default value

As has been mentioned, you may run into several issues if you use ISNUMERIC:

-- Incorrectly gives 0:

-- Error (conversion failure):

-- Error (overflow):
SELECT CASE WHEN ISNUMERIC('9999999999') = 1 THEN CAST('9999999999' AS INT) END

If you want a reliable conversion, you'll need to code one yourself.

Update: My new recommendation would be to use an intermediary test conversion to FLOAT to validate the number. This approach is based on adrianm's comment. The logic can be defined as an inline table-valued function:

        CASE WHEN ISNUMERIC(@text + '.e0') = 1 THEN 
             CASE WHEN CONVERT(FLOAT, @text) BETWEEN -2147483648 AND 2147483647 
                  THEN CONVERT(INT, @text) 
         END AS [Result]

Some tests:

SELECT [Conversion].[Result]
     ( '1234'                     )   -- 1234
   , ( '1,234'                    )   -- NULL
   , ( '1234.0'                   )   -- NULL
   , ( '-1234'                    )   -- -1234
   , ( '$1234'                    )   -- NULL
   , ( '1234e10'                  )   -- NULL
   , ( '1234 5678'                )   -- NULL
   , ( '123-456'                  )   -- NULL
   , ( '1234.5'                   )   -- NULL
   , ( '123456789000000'          )   -- NULL
   , ( 'N/A'                      )   -- NULL
   , ( '-'                        )   -- NULL
   , ( '$'                        )   -- NULL
   , ( '4.4'                      )   -- NULL
   , ( '1,300'                    )   -- NULL
   , ( '9999999999'               )   -- NULL
   , ( '00000000000000001234'     )   -- 1234
   , ( '212110090000000235698741' )   -- NULL
) AS [Source] ([Text])
OUTER APPLY TryConvertInt ([Source].[Text]) AS [Conversion]

Results are similar to Joseph Sturtevant's answer, with the following main differences:

  • My logic does not tolerate occurrences of . or , in order to mimic the behaviour of native INT conversions. '1,234' and '1234.0' return NULL.
  • Since it does not use local variables, my function can be defined as an inline table-valued function, allowing for better query optimization.
  • Joseph's answer can lead to incorrect results due to silent truncations of the argument; '00000000000000001234' evaluates to 12. Increasing the parameter length would result in errors on numbers that overflow BIGINT, such as BBANs (basic bank account numbers) like '212110090000000235698741'.

Withdrawn: The approach below is no longer recommended, as is left just for reference.

The snippet below works on non-negative integers. It checks that your string does not contain any non-digit characters, is not empty, and does not overflow (by exceeding the maximum value for the int type). However, it also gives NULL for valid integers whose length exceeds 10 characters due to leading zeros.

    CASE WHEN @text NOT LIKE '%[^0-9]%' THEN
         CASE WHEN LEN(@text) BETWEEN 1 AND 9 
                OR LEN(@text) = 10 AND @text <= '2147483647' 
              THEN CAST (@text AS INT)

If you want to support any number of leading zeros, use the below. The nested CASE statements, albeit unwieldy, are required to promote short-circuit evaluation and reduce the likelihood of errors (arising, for example, from passing a negative length to LEFT).

    CASE WHEN @text NOT LIKE '%[^0-9]%' THEN
         CASE WHEN LEN(@text) BETWEEN 1 AND 9 THEN CAST (@text AS INT)
              WHEN LEN(@text) >= 10 THEN
              CASE WHEN LEFT(@text, LEN(@text) - 10) NOT LIKE '%[^0]%'
                    AND RIGHT(@text, 10) <= '2147483647'
                   THEN CAST (@text AS INT)

If you want to support positive and negative integers with any number of leading zeros:

         -- Positive integers (or 0):
    CASE WHEN @text NOT LIKE '%[^0-9]%' THEN
         CASE WHEN LEN(@text) BETWEEN 1 AND 9 THEN CAST (@text AS INT)
              WHEN LEN(@text) >= 10 THEN
              CASE WHEN LEFT(@text, LEN(@text) - 10) NOT LIKE '%[^0]%'
                    AND RIGHT(@text, 10) <= '2147483647'
                   THEN CAST (@text AS INT)
         -- Negative integers:
         WHEN LEFT(@text, 1) = '-' THEN
         CASE WHEN RIGHT(@text, LEN(@text) - 1) NOT LIKE '%[^0-9]%' THEN
              CASE WHEN LEN(@text) BETWEEN 2 AND 10 THEN CAST (@text AS INT)
                   WHEN LEN(@text) >= 11 THEN
                   CASE WHEN SUBSTRING(@text, 2, LEN(@text) - 11) NOT LIKE '%[^0]%'
                         AND RIGHT(@text, 10) <= '2147483648'
                        THEN CAST (@text AS INT)

How to get an isoformat datetime string including the default timezone?

You can do it in Python 2.7+ with python-dateutil (which is insalled on Mac by default):

>>> from datetime import datetime
>>> from import tzlocal

Or you if you want to convert from an existed stored string:

>>> from datetime import datetime
>>> from import tzlocal
>>> from dateutil.parser import parse
>>> parse("2016-10-21T16:33:27.696173").replace(tzinfo=tzlocal()).isoformat()
'2016-10-21T16:33:27.696173-03:00' <-- Atlantic Daylight Time (ADT) 
>>> parse("2016-01-21T16:33:27.696173").replace(tzinfo=tzlocal()).isoformat()
'2016-01-21T16:33:27.696173-04:00' <-- Atlantic Standard Time (AST)

Is there a simple way to increment a datetime object one month in Python?

Note: This answer shows how to achieve this using only the datetime and calendar standard library (stdlib) modules - which is what was explicitly asked for. The accepted answer shows how to better achieve this with one of the many dedicated non-stdlib libraries. If you can use non-stdlib libraries, by all means do so for these kinds of date/time manipulations!

How about this?

def add_one_month(orig_date):
    # advance year and month by one month
    new_year = orig_date.year
    new_month = orig_date.month + 1
    # note: in, months go from 1 to 12
    if new_month > 12:
        new_year += 1
        new_month -= 12

    new_day =
    # while day is out of range for month, reduce by one
    while True:
            new_date =, new_month, new_day)
        except ValueError as e:
            new_day -= 1

    return new_date


Improved version which:

  1. keeps the time information if given a datetime.datetime object
  2. doesn't use try/catch, instead using calendar.monthrange from the calendar module in the stdlib:
import datetime
import calendar

def add_one_month(orig_date):
    # advance year and month by one month
    new_year = orig_date.year
    new_month = orig_date.month + 1
    # note: in, months go from 1 to 12
    if new_month > 12:
        new_year += 1
        new_month -= 12

    last_day_of_month = calendar.monthrange(new_year, new_month)[1]
    new_day = min(, last_day_of_month)

    return orig_date.replace(year=new_year, month=new_month, day=new_day)

How to find a min/max with Ruby

You can use




It's a method for Arrays.

How to get an element by its href in jquery?

Yes, you can use jQuery's attribute selector for that.

var linksToGoogle = $('a[href=""]');

Alternatively, if your interest is rather links starting with a certain URL, use the attribute-starts-with selector:

var allLinksToGoogle = $('a[href^=""]');

Core dump file is not generated

In centos,if you are not root account to generate core file: you must be set the account has a root privilege or login root account:

vim /etc/security/limits.conf

account soft core unlimited
account hard core unlimited

then if you in login shell with securecrt or other:

logout and then relogin

What's the difference between HEAD^ and HEAD~ in Git?

actual example of the difference between HEAD~ and HEAD^


Thread-safe List<T> property

Here is the class you asked for:

namespace AI.Collections {
    using System;
    using System.Collections;
    using System.Collections.Generic;
    using System.Linq;
    using System.Runtime.Serialization;
    using System.Threading.Tasks;
    using System.Threading.Tasks.Dataflow;

    /// <summary>
    ///     Just a simple thread safe collection.
    /// </summary>
    /// <typeparam name="T"></typeparam>
    /// <value>Version 1.5</value>
    /// <remarks>TODO replace locks with AsyncLocks</remarks>
    [DataContract( IsReference = true )]
    public class ThreadSafeList<T> : IList<T> {
        /// <summary>
        ///     TODO replace the locks with a ReaderWriterLockSlim
        /// </summary>
        private readonly List<T> _items = new List<T>();

        public ThreadSafeList( IEnumerable<T> items = null ) { this.Add( items ); }

        public long LongCount {
            get {
                lock ( this._items ) {
                    return this._items.LongCount();

        public IEnumerator<T> GetEnumerator() { return this.Clone().GetEnumerator(); }

        IEnumerator IEnumerable.GetEnumerator() { return this.GetEnumerator(); }

        public void Add( T item ) {
            if ( Equals( default( T ), item ) ) {
            lock ( this._items ) {
                this._items.Add( item );

        public Boolean TryAdd( T item ) {
            try {
                if ( Equals( default( T ), item ) ) {
                    return false;
                lock ( this._items ) {
                    this._items.Add( item );
                    return true;
            catch ( NullReferenceException ) { }
            catch ( ObjectDisposedException ) { }
            catch ( ArgumentNullException ) { }
            catch ( ArgumentOutOfRangeException ) { }
            catch ( ArgumentException ) { }
            return false;

        public void Clear() {
            lock ( this._items ) {

        public bool Contains( T item ) {
            lock ( this._items ) {
                return this._items.Contains( item );

        public void CopyTo( T[] array, int arrayIndex ) {
            lock ( this._items ) {
                this._items.CopyTo( array, arrayIndex );

        public bool Remove( T item ) {
            lock ( this._items ) {
                return this._items.Remove( item );

        public int Count {
            get {
                lock ( this._items ) {
                    return this._items.Count;

        public bool IsReadOnly { get { return false; } }

        public int IndexOf( T item ) {
            lock ( this._items ) {
                return this._items.IndexOf( item );

        public void Insert( int index, T item ) {
            lock ( this._items ) {
                this._items.Insert( index, item );

        public void RemoveAt( int index ) {
            lock ( this._items ) {
                this._items.RemoveAt( index );

        public T this[ int index ] {
            get {
                lock ( this._items ) {
                    return this._items[ index ];
            set {
                lock ( this._items ) {
                    this._items[ index ] = value;

        /// <summary>
        ///     Add in an enumerable of items.
        /// </summary>
        /// <param name="collection"></param>
        /// <param name="asParallel"></param>
        public void Add( IEnumerable<T> collection, Boolean asParallel = true ) {
            if ( collection == null ) {
            lock ( this._items ) {
                this._items.AddRange( asParallel
                                              ? collection.AsParallel().Where( arg => !Equals( default( T ), arg ) )
                                              : collection.Where( arg => !Equals( default( T ), arg ) ) );

        public Task AddAsync( T item ) {
            return Task.Factory.StartNew( () => { this.TryAdd( item ); } );

        /// <summary>
        ///     Add in an enumerable of items.
        /// </summary>
        /// <param name="collection"></param>
        public Task AddAsync( IEnumerable<T> collection ) {
            if ( collection == null ) {
                throw new ArgumentNullException( "collection" );

            var produce = new TransformBlock<T, T>( item => item, new ExecutionDataflowBlockOptions { MaxDegreeOfParallelism = Environment.ProcessorCount } );

            var consume = new ActionBlock<T>( action: async obj => await this.AddAsync( obj ), dataflowBlockOptions: new ExecutionDataflowBlockOptions { MaxDegreeOfParallelism = Environment.ProcessorCount } );
            produce.LinkTo( consume );

            return Task.Factory.StartNew( async () => {
                collection.AsParallel().ForAll( item => produce.SendAsync( item ) );
                await consume.Completion;
            } );

        /// <summary>
        ///     Returns a new copy of all items in the <see cref="List{T}" />.
        /// </summary>
        /// <returns></returns>
        public List<T> Clone( Boolean asParallel = true ) {
            lock ( this._items ) {
                return asParallel
                               ? new List<T>( this._items.AsParallel() )
                               : new List<T>( this._items );

        /// <summary>
        ///     Perform the <paramref name="action" /> on each item in the list.
        /// </summary>
        /// <param name="action">
        ///     <paramref name="action" /> to perform on each item.
        /// </param>
        /// <param name="performActionOnClones">
        ///     If true, the <paramref name="action" /> will be performed on a <see cref="Clone" /> of the items.
        /// </param>
        /// <param name="asParallel">
        ///     Use the <see cref="ParallelQuery{TSource}" /> method.
        /// </param>
        /// <param name="inParallel">
        ///     Use the
        ///     <see
        ///         cref="Parallel.ForEach{TSource}(System.Collections.Generic.IEnumerable{TSource},System.Action{TSource})" />
        ///     method.
        /// </param>
        public void ForEach( Action<T> action, Boolean performActionOnClones = true, Boolean asParallel = true, Boolean inParallel = false ) {
            if ( action == null ) {
                throw new ArgumentNullException( "action" );
            var wrapper = new Action<T>( obj => {
                try {
                    action( obj );
                catch ( ArgumentNullException ) {
                    //if a null gets into the list then swallow an ArgumentNullException so we can continue adding
            } );
            if ( performActionOnClones ) {
                var clones = this.Clone( asParallel: asParallel );
                if ( asParallel ) {
                    clones.AsParallel().ForAll( wrapper );
                else if ( inParallel ) {
                    Parallel.ForEach( clones, wrapper );
                else {
                    clones.ForEach( wrapper );
            else {
                lock ( this._items ) {
                    if ( asParallel ) {
                        this._items.AsParallel().ForAll( wrapper );
                    else if ( inParallel ) {
                        Parallel.ForEach( this._items, wrapper );
                    else {
                        this._items.ForEach( wrapper );

        /// <summary>
        ///     Perform the <paramref name="action" /> on each item in the list.
        /// </summary>
        /// <param name="action">
        ///     <paramref name="action" /> to perform on each item.
        /// </param>
        /// <param name="performActionOnClones">
        ///     If true, the <paramref name="action" /> will be performed on a <see cref="Clone" /> of the items.
        /// </param>
        /// <param name="asParallel">
        ///     Use the <see cref="ParallelQuery{TSource}" /> method.
        /// </param>
        /// <param name="inParallel">
        ///     Use the
        ///     <see
        ///         cref="Parallel.ForEach{TSource}(System.Collections.Generic.IEnumerable{TSource},System.Action{TSource})" />
        ///     method.
        /// </param>
        public void ForAll( Action<T> action, Boolean performActionOnClones = true, Boolean asParallel = true, Boolean inParallel = false ) {
            if ( action == null ) {
                throw new ArgumentNullException( "action" );
            var wrapper = new Action<T>( obj => {
                try {
                    action( obj );
                catch ( ArgumentNullException ) {
                    //if a null gets into the list then swallow an ArgumentNullException so we can continue adding
            } );
            if ( performActionOnClones ) {
                var clones = this.Clone( asParallel: asParallel );
                if ( asParallel ) {
                    clones.AsParallel().ForAll( wrapper );
                else if ( inParallel ) {
                    Parallel.ForEach( clones, wrapper );
                else {
                    clones.ForEach( wrapper );
            else {
                lock ( this._items ) {
                    if ( asParallel ) {
                        this._items.AsParallel().ForAll( wrapper );
                    else if ( inParallel ) {
                        Parallel.ForEach( this._items, wrapper );
                    else {
                        this._items.ForEach( wrapper );

SSL certificate rejected trying to access GitHub over HTTPS behind firewall

To clone on windows while setting SSL verify to false:

    git -c http.sslVerify=false clone

If you want to clone without borfing your global settings.

iOS for VirtualBox

Additional to the above - the QEMU website has good documentation about setting up an ARM based emulator:

How do I combine 2 javascript variables into a string

warning! this does not work with links.

var variable = 'variable', another = 'another';

['I would', 'like to'].join(' ') + ' a js ' + variable + ' together with ' + another + ' to create ' + [another, ...[variable].concat('name')].join(' ').concat('...');

Cannot find Dumpbin.exe

By default, it's not in your PATH. You need to use the "Visual Studio 2005 Command Prompt". Alternatively, you can run the vsvars32 batch file, which will set up your environment correctly.

Conveniently, the path to this is stored in the VS80COMNTOOLS environment variable.

Setting dynamic scope variables in AngularJs - scope.<some_string>

The solution I have found is to use $parse.

"Converts Angular expression into a function."

If anyone has a better one please add a new answer to the question!

Here is the example:

var the_string = 'life.meaning';

// Get the model
var model = $parse(the_string);

// Assigns a value to it
model.assign($scope, 42);

// Apply it to the scope
// $scope.$apply(); <- According to comments, this is no longer needed

console.log($;  // logs 42

How can I wrap or break long text/word in a fixed width span?

In my case, display: block was breaking the design as intended.

The max-width property just saved me.

and for styling, you can use text-overflow: ellipsis as well.

my code was

max-width: 255px

Makefile If-Then Else and Loops

Have you tried the GNU make documentation? It has a whole section about conditionals with examples.

How to remove duplicates from Python list and keep order?

For the string data

 output = []

     def uniq(input):
         if input not in output:
 print output     

C# DateTime.ParseExact

It's probably the same problem with cultures as presented in this related SO-thread: Why can't DateTime.ParseExact() parse "9/1/2009" using "M/d/yyyy"

You already specified the culture, so try escaping the slashes.

AngularJS documentation?


How and where is used? After module definition or after app.config(), after app.controller()?


In your package.js E.g. /packages/dashboard/public/controllers/dashboard.js


Make it look like this

var app = angular.module('mean.dashboard', ['ui.bootstrap']);

app.controller('DashboardController', ['$scope', 'Global', 'Dashboard',
    function($scope, Global, Dashboard) {
        $ = Global;
        $scope.package = {
            name: 'dashboard'
        // ...
]); {
    editableOptions.theme = 'bs3'; // bootstrap3 theme. Can be also 'bs2', 'default'

Why doesn't calling a Python string method do anything unless you assign its output?

All string functions as lower, upper, strip are returning a string without modifying the original. If you try to modify a string, as you might think well it is an iterable, it will fail.

x = 'hello'
x[0] = 'i' #'str' object does not support item assignment

There is a good reading about the importance of strings being immutable: Why are Python strings immutable? Best practices for using them

Does document.body.innerHTML = "" clear the web page?

document.body.innerHTML = ''; does clear the body, yeah. But it clears the innerHTML as it is at the moment the code is ran. As you run the code before the images and the script are actually in the body, it tries to clear the body, but there's nothing to clear.

If you want to clear the body, you have to run the code after the body has been filled with content. You can do this by either placing the <script> block as the last child of body, so everything is loaded before the code is ran, or you have to use some way to listen to the dom:loaded event.

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' )

Setting an HTML text input box's "default" value. Revert the value when clicking ESC

This esc behavior is IE only by the way. Instead of using jQuery use good old javascript for creating the element and it works.

var element = document.createElement('input');
element.type = 'text';
element.value = 100;

If you want to extend this functionality to other browsers then I would use jQuery's data object to store the default. Then set it when user presses escape.

//store default value for all elements on page. set new default on blur
$('input').each( function() {
    $(this).data('default', $(this).val());
    $(this).blur( function() { $(this).data('default', $(this).val()); });

$('input').keyup( function(e) {
    if (e.keyCode == 27) { $(this).val($(this).data('default')); }

Ping a site in Python?

using system ping command to ping a list of hosts:

import re
from subprocess import Popen, PIPE
from threading import Thread

class Pinger(object):
    def __init__(self, hosts):
        for host in hosts:
            pa = PingAgent(host)

class PingAgent(Thread):
    def __init__(self, host):
        Thread.__init__(self)        = host

    def run(self):
        p = Popen('ping -n 1 ' +, stdout=PIPE)
        m ='Average = (.*)ms',
        if m: print 'Round Trip Time: %s ms -' %,
        else: print 'Error: Invalid Response -',

if __name__ == '__main__':
    hosts = [

MYSQL Truncated incorrect DOUBLE value

Mainly invalid query strings will give this warning.

Wrong due to a subtle syntax error (misplaced right parenthesis) when using INSTR function:

INSERT INTO users (user_name) SELECT name FROM site_users WHERE
INSTR(status, 'active'>0);


INSERT INTO users (user_name) SELECT name FROM site_users WHERE
INSTR(status, 'active')>0;

Typescript ReferenceError: exports is not defined

for me, removing "esModuleInterop": true from tsconfig.json did the trick.

Count unique values using pandas groupby

I think you can use SeriesGroupBy.nunique:

print (df.groupby('param')['group'].nunique())
a    2
b    1
Name: group, dtype: int64

Another solution with unique, then create new df by DataFrame.from_records, reshape to Series by stack and last value_counts:

a = df[df.param.notnull()].groupby('group')['param'].unique()
print (pd.DataFrame.from_records(a.values.tolist()).stack().value_counts())
a    2
b    1
dtype: int64

Hive load CSV with commas in quoted fields

keep the delimiter in single quotes it will work.


This will work

How do I generate a SALT in Java for Salted-Hash?

Inspired from this post and that post, I use this code to generate and verify hashed salted passwords. It only uses JDK provided classes, no external dependency.

The process is:

  • you create a salt with getNextSalt
  • you ask the user his password and use the hash method to generate a salted and hashed password. The method returns a byte[] which you can save as is in a database with the salt
  • to authenticate a user, you ask his password, retrieve the salt and hashed password from the database and use the isExpectedPassword method to check that the details match
 * A utility class to hash passwords and check passwords vs hashed values. It uses a combination of hashing and unique
 * salt. The algorithm used is PBKDF2WithHmacSHA1 which, although not the best for hashing password (vs. bcrypt) is
 * still considered robust and <a href=""> recommended by NIST </a>.
 * The hashed value has 256 bits.
public class Passwords {

  private static final Random RANDOM = new SecureRandom();
  private static final int ITERATIONS = 10000;
  private static final int KEY_LENGTH = 256;

   * static utility class
  private Passwords() { }

   * Returns a random salt to be used to hash a password.
   * @return a 16 bytes random salt
  public static byte[] getNextSalt() {
    byte[] salt = new byte[16];
    return salt;

   * Returns a salted and hashed password using the provided hash.<br>
   * Note - side effect: the password is destroyed (the char[] is filled with zeros)
   * @param password the password to be hashed
   * @param salt     a 16 bytes salt, ideally obtained with the getNextSalt method
   * @return the hashed password with a pinch of salt
  public static byte[] hash(char[] password, byte[] salt) {
    PBEKeySpec spec = new PBEKeySpec(password, salt, ITERATIONS, KEY_LENGTH);
    Arrays.fill(password, Character.MIN_VALUE);
    try {
      SecretKeyFactory skf = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1");
      return skf.generateSecret(spec).getEncoded();
    } catch (NoSuchAlgorithmException | InvalidKeySpecException e) {
      throw new AssertionError("Error while hashing a password: " + e.getMessage(), e);
    } finally {

   * Returns true if the given password and salt match the hashed value, false otherwise.<br>
   * Note - side effect: the password is destroyed (the char[] is filled with zeros)
   * @param password     the password to check
   * @param salt         the salt used to hash the password
   * @param expectedHash the expected hashed value of the password
   * @return true if the given password and salt match the hashed value, false otherwise
  public static boolean isExpectedPassword(char[] password, byte[] salt, byte[] expectedHash) {
    byte[] pwdHash = hash(password, salt);
    Arrays.fill(password, Character.MIN_VALUE);
    if (pwdHash.length != expectedHash.length) return false;
    for (int i = 0; i < pwdHash.length; i++) {
      if (pwdHash[i] != expectedHash[i]) return false;
    return true;

   * Generates a random password of a given length, using letters and digits.
   * @param length the length of the password
   * @return a random password
  public static String generateRandomPassword(int length) {
    StringBuilder sb = new StringBuilder(length);
    for (int i = 0; i < length; i++) {
      int c = RANDOM.nextInt(62);
      if (c <= 9) {
      } else if (c < 36) {
        sb.append((char) ('a' + c - 10));
      } else {
        sb.append((char) ('A' + c - 36));
    return sb.toString();

Set Encoding of File to UTF8 With BOM in Sublime Text 3

Into Preferences > Settings - Users
File : Preferences.sublime-settings

Write this :

"show_encoding" : true,

It's explain on the release note date 17 December 2013. Build 3059. Official site Sublime Text 3

TypeError: $(...).autocomplete is not a function

you missed jquery ui library. Use CDN of Jquery UI or if you want it locally then download the file from Jquery Ui

<link href="" rel="Stylesheet"></link>
<script src="YourJquery source path"></script>
<script src="" ></script>

Getting the URL of the current page using Selenium WebDriver

Put sleep. It will work. I have tried. The reason is that the page wasn't loaded yet. Check this question to know how to wait for load - Wait for page load in Selenium

How to silence output in a Bash script?

Try with:

myprogram &>/dev/null

to get no output

TypeScript error TS1005: ';' expected (II)

  • Remove C:\Program Files (x86)\Microsoft SDKs\TypeScript\1.0 directory.

  • Now run :

    npm install -g typescript 

    this will install the latest version and then re-try.

How to display activity indicator in middle of the iphone screen?

This is the correct way:

UIActivityIndicatorView *activityIndicator = [[UIActivityIndicatorView alloc]initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleGray]; = CGPointMake(self.view.frame.size.width / 2.0, self.view.frame.size.height / 2.0);
[self.view addSubview: activityIndicator];

[activityIndicator startAnimating];

[activityIndicator release];

Setup your autoresizing mask if you support rotation. Cheers!!!

Showing an image from console in Python

Why not just display it in the user's web browser?

Copy multiple files from one directory to another from Linux shell

I guess you are looking for brace expansion:

cp /home/ankur/folder/{file1,file2} /home/ankur/dest

take a look here, it would be helpful for you if you want to handle multiple files once :

tab completion with zsh...

enter image description here

Uses of content-disposition in an HTTP response header

Well, it seems that the Content-Disposition header was originally created for e-mail, not the web. (Link to relevant RFC.)

I'm guessing that web browsers may respond to

Response.AppendHeader("content-disposition", "inline; filename=" + fileName);

when saving, but I'm not sure.

Math constant PI value in C

Depending on the library you are using the standard GNU C Predefined Mathematical Constants are here...

You already have them so why redefine them? Your system desktop calculators probably have them and are even more accurate so you could but just be sure you're not conflicting with existing defined ones to save on compile warnings as they tend to get defaults for things like that. Enjoy!

Get MAC address using shell script

This was the only thing that worked for me on Armbian:

dmesg | grep -oE 'mac=.*\w+' | cut -b '5-'

How to get main div container to align to centre?

You can text-align: center the body to center the container. Then text-align: left the container to get all the text, etc. to align left.

How can I troubleshoot Python "Could not find platform independent libraries <prefix>"

change PYTHONHOME to the parent folder of the bin file of python, like /usr,which is the parent folder of /usr/bin.

Problem with SMTP authentication in PHP using PHPMailer, with Pear Mail works

Exim 4 requires that AUTH command only be sent after the client issued EHLO - attempts to authenticate without EHLO would be rejected. Some mailservers require that EHLO be issued twice. PHPMailer apparently fails to do so. If PHPMailer does not allow you to force EHLO initiation, you really should switch to SwiftMailer 4.

Concat scripts in order with Gulp

Apparently you can pass in the "nosort" option to gulp.src gulp.src.

How to implement onBackPressed() in Fragments?

Inside the fragment's onCreate method add the following:

public void onCreate(Bundle savedInstanceState) {

    OnBackPressedCallback callback = new OnBackPressedCallback(true) {
        public void handleOnBackPressed() {
            //Handle the back pressed
    requireActivity().getOnBackPressedDispatcher().addCallback(this, callback);

Replacing a 32-bit loop counter with 64-bit introduces crazy performance deviations with _mm_popcnt_u64 on Intel CPUs

First of all, try to estimate peak performance - examine, in particular, Appendix C.

In your case, it's table C-10 that shows POPCNT instruction has latency = 3 clocks and throughput = 1 clock. Throughput shows your maximal rate in clocks (multiply by core frequency and 8 bytes in case of popcnt64 to get your best possible bandwidth number).

Now examine what compiler did and sum up throughputs of all other instructions in the loop. This will give best possible estimate for generated code.

At last, look at data dependencies between instructions in the loop as they will force latency-large delay instead of throughput - so split instructions of single iteration on data flow chains and calculate latency across them then naively pick up maximal from them. it will give rough estimate taking into account data flow dependencies.

However, in your case, just writing code the right way would eliminate all these complexities. Instead of accumulating to the same count variable, just accumulate to different ones (like count0, count1, ... count8) and sum them up at the end. Or even create an array of counts[8] and accumulate to its elements - perhaps, it will be vectorized even and you will get much better throughput.

P.S. and never run benchmark for a second, first warm up the core then run loop for at least 10 seconds or better 100 seconds. otherwise, you will test power management firmware and DVFS implementation in hardware :)

P.P.S. I heard endless debates on how much time should benchmark really run. Most smartest folks are even asking why 10 seconds not 11 or 12. I should admit this is funny in theory. In practice, you just go and run benchmark hundred times in a row and record deviations. That IS funny. Most people do change source and run bench after that exactly ONCE to capture new performance record. Do the right things right.

Not convinced still? Just use above C-version of benchmark by assp1r1n3 ( and try 100 instead of 10000 in retry loop.

My 7960X shows, with RETRY=100:

Count: 203182300 Elapsed: 0.008385 seconds Speed: 12.505379 GB/s

Count: 203182300 Elapsed: 0.011063 seconds Speed: 9.478225 GB/s

Count: 203182300 Elapsed: 0.011188 seconds Speed: 9.372327 GB/s

Count: 203182300 Elapsed: 0.010393 seconds Speed: 10.089252 GB/s

Count: 203182300 Elapsed: 0.009076 seconds Speed: 11.553283 GB/s

with RETRY=10000:

Count: 20318230000 Elapsed: 0.661791 seconds Speed: 15.844519 GB/s

Count: 20318230000 Elapsed: 0.665422 seconds Speed: 15.758060 GB/s

Count: 20318230000 Elapsed: 0.660983 seconds Speed: 15.863888 GB/s

Count: 20318230000 Elapsed: 0.665337 seconds Speed: 15.760073 GB/s

Count: 20318230000 Elapsed: 0.662138 seconds Speed: 15.836215 GB/s

P.P.P.S. Finally, on "accepted answer" and other mistery ;-)

Let's use assp1r1n3's answer - he has 2.5Ghz core. POPCNT has 1 clock throuhgput, his code is using 64-bit popcnt. So math is 2.5Ghz * 1 clock * 8 bytes = 20 GB/s for his setup. He is seeing 25Gb/s, perhaps due to turbo boost to around 3Ghz.

Thus go to and look for i7-4870HQ:

That core could run up to 3.7Ghz and real maximal rate is 29.6 GB/s for his hardware. So where is another 4GB/s? Perhaps, it's spent on loop logic and other surrounding code within each iteration.

Now where is this false dependency? hardware runs at almost peak rate. Maybe my math is bad, it happens sometimes :)

P.P.P.P.P.S. Still people suggesting HW errata is culprit, so I follow suggestion and created inline asm example, see below.

On my 7960X, first version (with single output to cnt0) runs at 11MB/s, second version (with output to cnt0, cnt1, cnt2 and cnt3) runs at 33MB/s. And one could say - voila! it's output dependency.

OK, maybe, the point I made is that it does not make sense to write code like this and it's not output dependency problem but dumb code generation. We are not testing hardware, we are writing code to unleash maximal performance. You could expect that HW OOO should rename and hide those "output-dependencies" but, gash, just do the right things right and you will never face any mystery.

uint64_t builtin_popcnt1a(const uint64_t* buf, size_t len) 
    uint64_t cnt0, cnt1, cnt2, cnt3;
    cnt0 = cnt1 = cnt2 = cnt3 = 0;
    uint64_t val = buf[0];
    #if 0
        __asm__ __volatile__ (
            "popcnt %2, %1\n\t"
            "popcnt %2, %1\n\t"
            "popcnt %2, %1\n\t"
            "popcnt %2, %1\n\t"
            "subq $4, %0\n\t"
            "jnz 1b\n\t"
        : "+q" (len), "=q" (cnt0)
        : "q" (val)
        __asm__ __volatile__ (
            "popcnt %5, %1\n\t"
            "popcnt %5, %2\n\t"
            "popcnt %5, %3\n\t"
            "popcnt %5, %4\n\t"
            "subq $4, %0\n\t"
            "jnz 1b\n\t"
        : "+q" (len), "=q" (cnt0), "=q" (cnt1), "=q" (cnt2), "=q" (cnt3)
        : "q" (val)
    return cnt0;

Gradle sync failed: failed to find Build Tools revision 24.0.0 rc1

Go to Build Gradle (Module:app) Change the following. In my case, I choose 25.0.3

android {

    compileSdkVersion 25
    buildToolsVersion "25.0.3"
    defaultConfig {
        applicationId "com.example.cesarhcq.viisolutions"
        minSdkVersion 15
        targetSdkVersion 25

After that, it works fine!

How to get build time stamp from Jenkins build variables?

One way this can be done is using shell script in global environment section, here, I am using UNIX timestamp but you can use any shell script syntax compatible time format:

pipeline {

    agent any

    environment {
        def BUILDVERSION = sh(script: "echo `date +%s`", returnStdout: true).trim()

    stages {
        stage("Awesome Stage") {
            steps {
                echo "Current build version :: $BUILDVERSION"

Generating an MD5 checksum of a file

You can use hashlib.md5()

Note that sometimes you won't be able to fit the whole file in memory. In that case, you'll have to read chunks of 4096 bytes sequentially and feed them to the md5 method:

import hashlib
def md5(fname):
    hash_md5 = hashlib.md5()
    with open(fname, "rb") as f:
        for chunk in iter(lambda:, b""):
    return hash_md5.hexdigest()

Note: hash_md5.hexdigest() will return the hex string representation for the digest, if you just need the packed bytes use return hash_md5.digest(), so you don't have to convert back.

Remove credentials from Git

Try using the below command.

git credential-manager

Here you can get various options to manage your credentials (check the below screen).

Enter image description here

Or you can even directly try this command:

git credential-manager uninstall

This will start prompting for passwords again on each server interaction request.

What requests do browsers' "F5" and "Ctrl + F5" refreshes generate?

IE7/8/9 seem to behave differently depending on whether the page has focus or not.

If you click on the page and CTRL+F5 then "Cache-Control: no-cache" is included in the request headers. If you click in the Location/Address bar then press CTRL+F5 it isn't.

How can I detect if Flash is installed and if not, display a hidden div that informs the user?

@Drewid's answer didn't work in my Firefox 25 if the flash plugin is just disabled but installed.

@invertedSpear's comment in that answer worked in firefox but not in any IE version.

So combined both their code and got this. Tested in Google Chrome 31, Firefox 25, IE 8-10. Thanks Drewid and invertedSpear :)

var hasFlash = false;
try {
  var fo = new ActiveXObject('ShockwaveFlash.ShockwaveFlash');
  if (fo) {
    hasFlash = true;
} catch (e) {
  if (navigator.mimeTypes
        && navigator.mimeTypes['application/x-shockwave-flash'] != undefined
        && navigator.mimeTypes['application/x-shockwave-flash'].enabledPlugin) {
    hasFlash = true;

Including external HTML file to another HTML file

The iframe element.

<iframe src="name.html"></iframe>

But content that you way to have appear on multiple pages is better handled using templates.

PowerShell script to return members of multiple security groups

Get-ADGroupMember "Group1" -recursive | Select-Object Name | Export-Csv c:\path\Groups.csv

I got this to work for me... I would assume that you could put "Group1, Group2, etc." or try a wildcard. I did pre-load AD into PowerShell before hand:

Get-Module -ListAvailable | Import-Module

How can I clear the Scanner buffer in Java?

Other people have suggested using in.nextLine() to clear the buffer, which works for single-line input. As comments point out, however, sometimes input can be multi-line.

You can instead create a new Scanner object where you want to clear the buffer if you are using and not some other InputStream.

in = new Scanner(;

If you do this, don't call in.close() first. Doing so will close, and so you will get NoSuchElementExceptions on subsequent calls to in.nextInt(); probably shouldn't be closed during your program.

(The above approach is specific to It might not be appropriate for other input streams.)

If you really need to close your Scanner object before creating a new one, this StackOverflow answer suggests creating an InputStream wrapper for that has its own close() method that doesn't close the wrapped stream. This is overkill for simple programs, though.

Calling a Javascript Function from Console

I just discovered this issue. I was able to get around it by using indirection. In each module define a function, lets call it indirect:

function indirect(js) { return eval(js); }

With that function in each module, you can then execute any code in the context of it.

E.g. if you had this import in your module:

import { imported_fn } from "./import.js";

You could then get the results of calling imported_fn from the console by doing this:


Using eval was my first thought, but it doesn't work. My hypothesis is that calling eval from the console remains in the context of console, and we need to execute in the context of the module.

What is pipe() function in Angular

RxJS Operators are functions that build on the observables foundation to enable sophisticated manipulation of collections.

For example, RxJS defines operators such as map(), filter(), concat(), and flatMap().

You can use pipes to link operators together. Pipes let you combine multiple functions into a single function.

The pipe() function takes as its arguments the functions you want to combine, and returns a new function that, when executed, runs the composed functions in sequence.

Set the value of an input field

I use 'setAttribute' function:

<input type="text" id="example"> // Setup text field 
<script type="text/javascript"> 
  document.getElementById("example").setAttribute('value','My default value');

How do I return the response from an asynchronous call?

Use a callback() function inside the foo() success. Try in this way. It is simple and easy to understand.  

var lat = "";
var lon = "";
function callback(data) {
    lat =;
    lon = data.lon;
function getLoc() {
    var url = ""
    $.getJSON(url, function(data) {


Python Pandas - Find difference between two data frames

A slight variation of the nice @liangli's solution that does not require to change the index of existing dataframes:

newdf = df1.drop(df1.join(df2.set_index('Name').index))

How to concatenate strings in a Windows batch file?

What about:

@echo off
set myvar="the list: "
for /r %%i in (*.doc) DO call :concat %%i
echo %myvar%
goto :eof

set myvar=%myvar% %1;
goto :eof

Compute mean and standard deviation by group for multiple variables in a data.frame

Here is probably the simplest way to go about it (with a reproducible example):

df <- data.frame(ID=rep(1:3, 3), Obs_1=rnorm(9), Obs_2=rnorm(9), Obs_3=rnorm(9))
ddply(df, .(ID), summarize, Obs_1_mean=mean(Obs_1), Obs_1_std_dev=sd(Obs_1),
  Obs_2_mean=mean(Obs_2), Obs_2_std_dev=sd(Obs_2))

   ID  Obs_1_mean Obs_1_std_dev  Obs_2_mean Obs_2_std_dev
1  1 -0.13994642     0.8258445 -0.15186380     0.4251405
2  2  1.49982393     0.2282299  0.50816036     0.5812907
3  3 -0.09269806     0.6115075 -0.01943867     1.3348792

EDIT: The following approach saves you a lot of typing when dealing with many columns.

ddply(df, .(ID), colwise(mean))

  ID      Obs_1      Obs_2      Obs_3
1  1 -0.3748831  0.1787371  1.0749142
2  2 -1.0363973  0.0157575 -0.8826969
3  3  1.0721708 -1.1339571 -0.5983944

ddply(df, .(ID), colwise(sd))

  ID     Obs_1     Obs_2     Obs_3
1  1 0.8732498 0.4853133 0.5945867
2  2 0.2978193 1.0451626 0.5235572
3  3 0.4796820 0.7563216 1.4404602

What file uses .md extension and how should I edit them?

If you are creating .md files for your .NET solutions I recommend the Visual Studio 2015 extension Markdown Editor as it has a preview panel so you can see your changes in real time.

EDIT: This also should now work with Visual Studio 2017.

How to Change Font Size in drawString Java

code example below:

g.setFont(new Font("TimesRoman", Font.PLAIN, 30));
g.drawString("Welcome to the Java Applet", 20 , 20);

Using Python, find anagrams for a list of words

Most of previous answers are correct, here is another way to compare two strings. The main benefit of using this strategy versus sort is space/time complexity which is n log of n.

1.Check the length of string

2.Build frequency Dictionary and compare if they both match then we have successfully identified anagram words

def char_frequency(word):
    frequency  = {}
    for char in word:
        #if character  is in frequency then increment the value
        if char in frequency:
            frequency[char] += 1
        #else add character and set it to 1
            frequency[char] = 1
    return frequency 

a_word ='google'
b_word ='ooggle'
#check length of the words 
if (len(a_word) != len(b_word)):
   print ("not anagram")
    #here we check the frequecy to see if we get the same
    if ( char_frequency(a_word) == char_frequency(b_word)):
        print("found anagram")
        print("no anagram")

Android - Back button in the title bar

If your activity does extend Activity

public class YourActivity extends Activity {

    protected void onCreate(Bundle savedInstanceState) {




If your action extends AppCompatActivity

public class YourActivity extends AppCompatActivity {

        protected void onCreate(Bundle savedInstanceState) {




Nothing more to do, See Add up action

[OPTIONAL] To explicitly define parent activity modify your Manifest.xml like this:

<application ... >
    <!-- The main/home activity (it has no parent activity) -->
        android:name="com.example.myfirstapp.MainActivity" ...>
    <!-- A child of the main activity -->
        android:name="com.example.myfirstapp.YourActivity "
        android:parentActivityName="com.example.myfirstapp.MainActivity" >
        <!-- Parent activity meta-data to support 4.0 and lower -->
            android:value="com.example.myfirstapp.MainActivity" />

See Specify the Parent Activity

What is the (best) way to manage permissions for Docker shared volumes?

A very elegant solution can be seen on the official redis image and in general in all official images.

Described in step-by-step process:

  • Create redis user/group before anything else

As seen on Dockerfile comments:

add our user and group first to make sure their IDs get assigned consistently, regardless of whatever dependencies get added

  • Install gosu with Dockerfile

gosu is an alternative of su / sudo for easy step-down from root user. (Redis is always run with redis user)

  • Configure /data volume and set it as workdir

By configuring the /data volume with the VOLUME /data command we now have a separate volume that can either be docker volume or bind-mounted to a host dir.

Configuring it as the workdir (WORKDIR /data) makes it be the default directory where commands are executed from.

  • Add docker-entrypoint file and set it as ENTRYPOINT with default CMD redis-server

This means that all container executions will run through the docker-entrypoint script, and by default the command to be run is redis-server.

docker-entrypoint is a script that does a simple function: Change ownership of current directory (/data) and step-down from root to redis user to run redis-server. (If the executed command is not redis-server, it will run the command directly.)

This has the following effect

If the /data directory is bind-mounted to the host, the docker-entrypoint will prepare the user permissions before running redis-server under redis user.

This gives you the ease-of-mind that there is zero-setup in order to run the container under any volume configuration.

Of course if you need to share the volume between different images you need to make sure they use the same userid/groupid otherwise the latest container will hijack the user permissions from the previous one.

How to select a single column with Entity Framework?

I'm a complete noob on Entity but this is how I would do it in theory...

var name = yourDbContext.MyTable.Find(1).Name;

If It's A Primary Key.

-- OR --

var name = yourDbContext.MyTable.SingleOrDefault(mytable => mytable.UserId == 1).Name;

-- OR --

For whole Column:

var names = yourDbContext.MyTable
.Where(mytable => mytable.UserId == 1)
.Select(column => column.Name); //You can '.ToList();' this....

But "oh Geez Rick, What do I know..."

How do I navigate to a parent route from a child route?

You can navigate to your parent root like this

this.router.navigate(['.'], { relativeTo: this.activeRoute.parent });

You will need to inject the current active Route in the constructor

    private router: Router,
    private activeRoute: ActivatedRoute) {


How to get the current time in YYYY-MM-DD HH:MI:Sec.Millisecond format in Java?

To complement the above answers, here is a small working example of a program that prints the current time and date, including milliseconds.

import java.text.SimpleDateFormat;
import java.util.Date;

public class test {
    public static void main(String argv[]){
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSS");
        Date now = new Date();
        String strDate = sdf.format(now);

Incorrect syntax near ''

Such unexpected problems can appear when you copy the code from a web page or email and the text contains unprintable characters like individual CR or LF and non-breaking spaces.

How to enable DataGridView sorting when user clicks on the column header?

You can use DataGridViewColoumnHeaderMouseClick event like this :

Private string order = String.Empty;
private void dgvDepartment_ColumnHeaderMouseClick(object sender, DataGridViewCellMouseEventArgs e)
    if (order == "d")
        order = "a";                
dataGridView1.DataSource = students.Select(s => new { ID = s.StudentId, RUDE = s.RUDE, Nombre = s.Name, Apellidos = s.LastNameFather + " " + s.LastNameMother, Nacido = s.DateOfBirth })   .OrderBy(s => s.Apellidos).ToList();
        order = "d";
        dataGridView1.DataSource = students.Select(s => new { ID = s.StudentId, RUDE = s.RUDE, Nombre = s.Name, Apellidos = s.LastNameFather + " " + s.LastNameMother, Nacido = s.DateOfBirth }.OrderByDescending(s => s.Apellidos)  .ToList()

How to find numbers from a string?

I was looking for the answer of the same question but for a while I found my own solution and I wanted to share it for other people who will need those codes in the future. Here is another solution without function.

Dim control As Boolean
Dim controlval As String
Dim resultval As String
Dim i as Integer

controlval = "A1B2C3D4"

For i = 1 To Len(controlval)
control = IsNumeric(Mid(controlval, i, 1))
If control = True Then resultval = resultval & Mid(controlval, i, 1)
Next i

resultval = 1234

Best solution to protect PHP code without encryption

You need to consider your objectives:

1) Are you trying to prevent people from reading/modifying your code? If yes, you'll need an obfuscation/encryption tool. I've used Zend Guard with good success.

2) Are you trying to prevent unauthorized redistribution of your code?? A EULA/proprietary license will give you the legal power to prevent that, but won't actually stop it. An key/activation scheme will allow you to actively monitor usage, but can be removed unless you also encrypt your code. Zend Guard also has capabilities to lock a particular script to a particular customer machine and/or create time limited versions of the code if that's what you want to do.

I'm not familiar with vBulletin and the like, but they'd either need to encrypt/obfuscate or trust their users to do the right thing. In the latter case they have the protection of having a EULA which prohibits the behaviors they find undesirable, and the legal system to back up breaches of the EULA.

If you're not prepared/able to take legal action to protect your software and you don't want to encrypt/obfuscate, your options are a) Release it with a EULA so you're have a legal option if you ever need it and hope for the best, or b) consider whether an open source license might be more appropriate and just allow redistribution.

Install psycopg2 on Ubuntu

This worked for me:

pip install psycopg2-binary

How to check if mod_rewrite is enabled in php?

For IIS heros and heroins:

No need to look for mod_rewrite. Just install Rewrite 2 module and then import .htaccess files.

Class has no member named

Maybe I am 6.5 years late. But I'm answering because others maybe searching still now. I faced the same problem and was searching everywhere. But then I realized I had written my code in an empty file. If you create a project and write your code in there, there won't be this error.

List columns with indexes in PostgreSQL

A little bit modified answer of @cope360:

create table test (a int, b int, c int, constraint pk_test primary key(c, a, b));
select i.relname as index_name,
       ix.indisunique as is_unique,
       a.attname as column_name,
from pg_class c
       inner join pg_index ix on c.oid=ix.indrelid
       inner join pg_class i on ix.indexrelid=i.oid
       inner join pg_attribute a on a.attrelid=c.oid and a.attnum=any(ix.indkey)
where c.oid='public.test'::regclass::oid
order by array_position(ix.indkey, a.attnum) asc;

This will show the index columns in correct order:

index_name      is_unique  column_name
pk_test         true       c
pk_test         true       a
pk_test         true       b

Java Try Catch Finally blocks without Catch

Java versions before version 7 allow for these three combinations of try-catch-finally...

try - catch
try - catch - finally
try - finally

finally block will be always executed no matter of what's going on in the try or/and catch block. so if there is no catch block, the exception won't be handled here.

However, you will still need an exception handler somewhere in your code - unless you want your application to crash completely of course. It depends on the architecture of your application exactly where that handler is.

  • Java try block must be followed by either catch or finally block.
  • For each try block there can be zero or more catch blocks, but only one finally block.
  • The finally block will not be executed if program exits(either by calling System.exit() or by causing a fatal error that causes the process to abort).

How to add System.Windows.Interactivity to project?

I have had the exact same problem with a solution, that System.Windows.Interactivity was required for one of the project in Visual Studio 2019, and I tried to install Blend for Visual Studio SDK for .NET from Visual Studio 2019 Individual components, but it did not exist in it.

The consequence of that, I was not able to build the project in my solution with repetitive of following similar error on different XAML parts of the project:

The tag 'Interaction.Behaviors' does not exist in XML namespace 'clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity'.

Image with all errors The above mentioned errors snapshot example

The solution, the way I solved it, is by installing Microsoft Expression Blend Software Development Kit (SDK) for .NET 4 from Microsoft.

Thanks to my colleague @felza, mentioned that System.Windows.Interactivity requires this sdk, that is suppose to be located in this folder:

C:\Program Files (x86)\Microsoft SDKs\Expression\Blend\.NETFramework\v4.0

In my case it was not installed. I have had this folder C:\Program Files (x86)\Microsoft SDKs with out Expression\Blend\.NETFramework\v4.0 folder inside it.

After installing it, all errors disappeared.

Is it safe to delete the "InetPub" folder?

it is safe to delete the inetpub it is only a cache.

How to read one single line of csv data in Python?

You can use Pandas library to read the first few lines from the huge dataset.

import pandas as pd

data = pd.read_csv("names.csv", nrows=1)

You can mention the number of lines to be read in the nrows parameter.

sh: 0: getcwd() failed: No such file or directory on cited drive

Please check the directory path whether exists or not. This error comes up if the folder doesn't exists from where you are running the command. Probably you have executed a remove command from same path in command line.

Simple way to check if a string contains another string in C?

if (strstr(request, "favicon") != NULL) {
    // contains

Write Base64-encoded image to file

No need to use BufferedImage, as you already have the image file in a byte array

    byte dearr[] = Base64.decodeBase64(crntImage);
    FileOutputStream fos = new FileOutputStream(new File("c:/decode/abc.bmp")); 

How to change the status bar color in Android?

To Change the color of the status bar go to res/values-v21/styles.xml and color of status bar

    <!-- Base application theme. -->
    <style name="AppTheme" parent="Theme.AppCompat.Light">
        <item name="colorPrimary">@color/color_primary</item>
        <item name="colorPrimaryDark">@color/color_secondary</item>
        <item name="colorAccent">@color/color_accent</item>
        <item name="android:statusBarColor">#0000FF</item>

How can I remove space (margin) above HTML header?

This css allowed chrome and firefox to render all other elements on my page normally and remove the margin above my h1 tag. Also, as a page is resized em can work better than px.

h1 {
  margin-top: -.3em;
  margin-bottom: 0em;

copy db file with adb pull results in 'permission denied' error

I had the same problem. My work around is to use adb shell and su. Next, copy the file to /sdcard/Download

Then, I can use adb pull to get the file.

How to stop java process gracefully?

Signalling in Linux can be done with "kill" (man kill for the available signals), you'd need the process ID to do that. (ps ax | grep java) or something like that, or store the process id when the process gets created (this is used in most linux startup files, see /etc/init.d)

Portable signalling can be done by integrating a SocketServer in your java application. It's not that difficult and gives you the freedom to send any command you want.

If you meant finally clauses in stead of finalizers; they do not get extecuted when System.exit() is called. Finalizers should work, but shouldn't really do anything more significant but print a debug statement. They're dangerous.

How can I convert String to Int?

int i = Convert.ToInt32(TextBoxD1.Text);

Show div on scrollDown after 800px

You can also, do this.

$(window).on("scroll", function () {
   if ($(this).scrollTop() > 800) {
      #code here
   } else {
      #code here

True/False vs 0/1 in MySQL

Some "front ends", with the "Use Booleans" option enabled, will treat all TINYINT(1) columns as Boolean, and vice versa.

This allows you to, in the application, use TRUE and FALSE rather than 1 and 0.

This doesn't affect the database at all, since it's implemented in the application.

There is not really a BOOLEAN type in MySQL. BOOLEAN is just a synonym for TINYINT(1), and TRUE and FALSE are synonyms for 1 and 0.

If the conversion is done in the compiler, there will be no difference in performance in the application. Otherwise, the difference still won't be noticeable.

You should use whichever method allows you to code more efficiently, though not using the feature may reduce dependency on that particular "front end" vendor.

Groovy / grails how to determine a data type?

To determine the class of an object simply call:


You can abbreviate this to someObject.class in most cases. However, if you use this on a Map it will try to retrieve the value with key 'class'. Because of this, I always use getClass() even though it's a little longer.

If you want to check if an object implements a particular interface or extends a particular class (e.g. Date) use:

(somObject instanceof Date)

or to check if the class of an object is exactly a particular class (not a subclass of it), use:

(somObject.getClass() == Date)

Read Post Data submitted to ASP.Net Form

NameValueCollection nvclc = Request.Form;
string   uName= nvclc ["txtUserName"];
string   pswod= nvclc ["txtPassword"];
//try login
CheckLogin(uName, pswod);

What's the difference between faking, mocking, and stubbing?

the thing that you assert on it,is called a mock object and everything else that just helped the test run, is a stub.

Unit Testing: DateTime.Now

The best strategy is to wrap the current time in an abstraction and inject that abstraction into the consumer.

Alternatively, you can also define a time abstraction as an Ambient Context:

public abstract class TimeProvider
    private static TimeProvider current =

    public static TimeProvider Current
       get { return TimeProvider.current; }
           if (value == null)
               throw new ArgumentNullException("value");
           TimeProvider.current = value; 

   public abstract DateTime UtcNow { get; }

   public static void ResetToDefault()
       TimeProvider.current = DefaultTimeProvider.Instance;

This will enable you to consume it like this:

var now = TimeProvider.Current.UtcNow;

In a unit test, you can replace TimeProvider.Current with a Test Double/Mock object. Example using Moq:

var timeMock = new Mock<TimeProvider>();
timeMock.SetupGet(tp => tp.UtcNow).Returns(new DateTime(2010, 3, 11));
TimeProvider.Current = timeMock.Object;

However, when unit testing with static state, always remember to tear down your fixture by calling TimeProvider.ResetToDefault().

YouTube Autoplay not working

mute=1 or muted=1 as suggested by @Fab will work. However, if you wish to enable autoplay with sound you should add allow="autoplay" to your embedded <iframe>.

<iframe type="text/html" src="" frameborder="0" allow="autoplay"></iframe>

This is officially supported and documented in Google's Autoplay Policy Changes 2017 post

Iframe delegation A feature policy allows developers to selectively enable and disable use of various browser features and APIs. Once an origin has received autoplay permission, it can delegate that permission to cross-origin iframes with a new feature policy for autoplay. Note that autoplay is allowed by default on same-origin iframes.

<!-- Autoplay is allowed. -->
<iframe src="" allow="autoplay">

<!-- Autoplay and Fullscreen are allowed. -->
<iframe src="" allow="autoplay; fullscreen">

When the feature policy for autoplay is disabled, calls to play() without a user gesture will reject the promise with a NotAllowedError DOMException. And the autoplay attribute will also be ignored.

How can I print the contents of a hash in Perl?

The answer depends on what is in your hash. If you have a simple hash a simple

print map { "$_ $h{$_}\n" } keys %h;


print "$_ $h{$_}\n" for keys %h;

will do, but if you have a hash that is populated with references you will something that can walk those references and produce a sensible output. This walking of the references is normally called serialization. There are many modules that implement different styles, some of the more popular ones are:

Due to the fact that Data::Dumper is part of the core Perl library, it is probably the most popular; however, some of the other modules have very good things to offer.

How to display string that contains HTML in twig template?

You can also use:

{{ word|striptags('<b>')|raw }}

so that only <b> tag will be allowed.

MySQL selecting yesterday's date

The simplest and best way to get yesterday's date is:

subdate(current_date, 1)

Your query would be:

    url as LINK,
    count(*) as timesExisted,
    sum(DateVisited between UNIX_TIMESTAMP(subdate(current_date, 1)) and
        UNIX_TIMESTAMP(current_date)) as timesVisitedYesterday
FROM mytable

For the curious, the reason that sum(condition) gives you the count of rows that satisfy the condition, which would otherwise require a cumbersome and wordy case statement, is that in mysql boolean values are 1 for true and 0 for false, so summing a condition effectively counts how many times it's true. Using this pattern can neaten up your SQL code.

Get dates from a week number in T-SQL

SELECT DATEADD(week, @weekNumber - 1, DATEADD(DAY, @@datefirst - DATEPART(weekday, CAST(YEAR(GETDATE()) AS VARCHAR) + '-01-01') - 6, CAST(YEAR(GETDATE()) AS VARCHAR) + '-01-01'))

How do I encode URI parameter values?

I wrote my own, it's short, super simple, and you can copy it if you like:

Changing case in Vim

See the following methods:

 ~    : Changes the case of current character

 guu  : Change current line from upper to lower.

 gUU  : Change current LINE from lower to upper.

 guw  : Change to end of current WORD from upper to lower.

 guaw : Change all of current WORD to lower.

 gUw  : Change to end of current WORD from lower to upper.

 gUaw : Change all of current WORD to upper.

 g~~  : Invert case to entire line

 g~w  : Invert case to current WORD

 guG : Change to lowercase until the end of document.

Bash script - variable content as a command to run

You just need to do:

count=$(cat last_queries.txt | wc -l)
$(perl test2 $count)

However, if you want to call your Perl command later, and that's why you want to assign it to a variable, then:

count=$(cat last_queries.txt | wc -l)
var="perl test2 $count" # You need double quotes to get your $count value substituted.


eval $var

As per Bash's help:

~$ help eval
eval: eval [arg ...]
    Execute arguments as a shell command.

    Combine ARGs into a single string, use the result as input to the shell,
    and execute the resulting commands.

    Exit Status:
    Returns exit status of command or success if command is null.

How to overwrite the output directory in spark

This overloaded version of the save function works for me:, org.apache.spark.sql.SaveMode.valueOf("Overwrite"))

The example above would overwrite an existing folder. The savemode can take these parameters as well (

Append: Append mode means that when saving a DataFrame to a data source, if data/table already exists, contents of the DataFrame are expected to be appended to existing data.

ErrorIfExists: ErrorIfExists mode means that when saving a DataFrame to a data source, if data already exists, an exception is expected to be thrown.

Ignore: Ignore mode means that when saving a DataFrame to a data source, if data already exists, the save operation is expected to not save the contents of the DataFrame and to not change the existing data.

Dockerfile if else condition with external arguments

I had a similar issue for setting proxy server on a container.

The solution I'm using is an entrypoint script, and another script for environment variables configuration. Using RUN, you assure the configuration script runs on build, and ENTRYPOINT when you run the container.

--build-arg is used on command line to set proxy user and password.

As I need the same environment variables on container startup, I used a file to "persist" it from build to run.

The entrypoint script looks like:

# Load the script of environment variables
. /root/
# Run the main container command
exec "$@"


function start_config {
read u p < /root/proxy_credentials

export HTTP_PROXY=http://$u:[email protected]:8080
export HTTPS_PROXY=https://$u:[email protected]:8080

/bin/cat <<EOF > /etc/apt/apt.conf 
Acquire::http::proxy "http://$u:[email protected]:8080";
Acquire::https::proxy "https://$u:[email protected]:8080";

if [ -s "/root/proxy_credentials" ]

And in the Dockerfile, configure:

# Base Image
FROM ubuntu:18.04

ARG user
ARG pass

USER root

# -z the length of STRING is zero
# [] are an alias for test command
# if $user is not empty, write credentials file
RUN if [ ! -z "$user" ]; then echo "${user} ${pass}">/root/proxy_credentials ; fi

#copy bash scripts
COPY /root

RUN ["/bin/bash", "-c", ". /root/"]

# Install dependencies and tools
#RUN apt-get update -y && \
#    apt-get install -yqq --no-install-recommends \
#    vim iputils-ping

CMD ["sh", "-c", "bash"]

Build without proxy settings

docker build -t img01 -f Dockerfile . 

Build with proxy settings

docker build -t img01 --build-arg user=<USER> --build-arg pass=<PASS> -f Dockerfile . 

Take a look here.

How to map with index in Ruby?

I have always enjoyed the syntax of this style:

a = [1, 2, 3, 4] { |el, index| el + index }
# => [1, 3, 5, 7]

Invoking each_with_index gets you an enumerator you can easily map over with your index available.

for each loop in groovy

Your code works fine.

def list = [["c":"d"], ["e":"f"], ["g":"h"]]
Map tmpHM = [1:"second (e:f)", 0:"first (c:d)", 2:"third (g:h)"]

for (objKey in tmpHM.keySet()) {   
    HashMap objHM = (HashMap) list.get(objKey);
    print("objHM: ${objHM}  , ")

prints objHM: [e:f] , objHM: [c:d] , objHM: [g:h] ,


Then click "edit in console", "execute script"

IFrame: This content cannot be displayed in a frame

The X-Frame-Options is defined in the Http Header and not in the <head> section of the page you want to use in the iframe.

Accepted values are: DENY, SAMEORIGIN and ALLOW-FROM "url"

EOFError: end of file reached issue with Net::HTTP

I had a similar problem with a request to a non-SSL service.

This blog suggested vaguely to try URI encoding the URL that is passed to 'get':

I took a shot at it, based on desperation, and in my limiting testing this seems to have fixed it for me. My new code is:

@http ='')  
@http = @http.start    
url = ''
req =
req.basic_auth USERNAME, API_KEY
res = @http.request(req) 

Note that I use @http.start as I want to maintain the HTTP session over multiple requests. Other than that, you might like to try the most relevant part which is: URI.encode(url) inside the get call

The application was unable to start correctly (0xc000007b)

I recently had an issue where I was developing an application (that used a serial port) and it worked on all the machines I tested it on but a few people were getting this error.

It turns out all the machines that the error happened on were running Win7 x64 and had NEVER ONCE been updated.

Running a Windows update fixed all of the machines in my particular case.

How to cut an entire line in vim and paste it?

Just three steps.

  1. Go to the start of the text, and press v
  2. Go to the end of the text, and press d
  3. Go to the place that you want to paste, and press p

How do I wrap text in a span?

Wrapping can be done in various ways. I'll mention 2 of them:

1.) text wrapping - using white-space property

2.) word wrapping - using word-wrap property

By the way, in order to work using these 2 approaches, I believe you need to set the "display" property to block of the corresponding span element.

However, as Kirill already mentioned, it's a good idea to think about it for a moment. You're talking about forcing the text into a paragraph. PARAGRAPH. That should ring some bells in your head, shouldn't it? ;)

How do I style (css) radio buttons and labels?

This will get your buttons and labels next to each other, at least. I believe the second part can't be done in css alone, and will need javascript. I found a page that might help you with that part as well, but I don't have time right now to try it out:

<style type="text/css">
.input input {
  float: left;
.input label {
  margin: 5px;
<div class="input radio">
        <legend>What color is the sky?</legend>
        <input type="hidden" name="data[Submit][question]" value="" id="SubmitQuestion" />

        <input type="radio" name="data[Submit][question]" id="SubmitQuestion1" value="1"  />
        <label for="SubmitQuestion1">A strange radient green.</label>

        <input type="radio" name="data[Submit][question]" id="SubmitQuestion2" value="2"  />
        <label for="SubmitQuestion2">A dark gloomy orange</label>
        <input type="radio" name="data[Submit][question]" id="SubmitQuestion3" value="3"  />
        <label for="SubmitQuestion3">A perfect glittering blue</label>

How to check the first character in a string in Bash or UNIX shell?

$ foo="/some/directory/file"
$ [ ${foo:0:1} == "/" ] && echo 1 || echo 0
$ foo="[email protected]:/some/directory/file"
$ [ ${foo:0:1} == "/" ] && echo 1 || echo 0

How to add a button programmatically in VBA next to some sheet cell data?

I think this is enough to get you on a nice path:

Sub a()
  Dim btn As Button
  Application.ScreenUpdating = False
  Dim t As Range
  For i = 2 To 6 Step 2
    Set t = ActiveSheet.Range(Cells(i, 3), Cells(i, 3))
    Set btn = ActiveSheet.Buttons.Add(t.Left, t.Top, t.Width, t.Height)
    With btn
      .OnAction = "btnS"
      .Caption = "Btn " & i
      .Name = "Btn" & i
    End With
  Next i
  Application.ScreenUpdating = True
End Sub

Sub btnS()
 MsgBox Application.Caller
End Sub

It creates the buttons and binds them to butnS(). In the btnS() sub, you should show your dialog, etc.

Mathematica graphics

How to remove frame from matplotlib (pyplot.figure vs matplotlib.figure ) (frameon=False Problematic in matplotlib)

plt.savefig(file_path, bbox_inches="tight", pad_inches = 0)

plt.savefig has those options in itself, just need to set axes off before

Copy table to a different database on a different SQL Server

Microsoft SQL Server Database Publishing Wizard will generate all the necessary insert statements, and optionally schema information as well if you need that:

Select second last element with css

In CSS3 you have:



nth-last-child Browser Support:

  • Chrome 2
  • Firefox 3.5
  • Opera 9.5, 10
  • Safari 3.1, 4
  • Internet Explorer 9

How to get the path of src/test/resources directory in JUnit?

With Spring you could easily read it from the resources folder (either main/resources or test/resources):

For example create a file: test/resources/subfolder/sample.json

public void testReadFile() {
    String json = this.readFile("classpath:subfolder/sample.json");

public String readFile(String path) {
    try {
        File file = ResourceUtils.getFile(path);
        return new String(Files.readAllBytes(file.toPath()));
    } catch (IOException e) {

    return null;

Python Pandas merge only certain columns

If you want to drop column(s) from the target data frame, but the column(s) are required for the join, you can do the following:

df1 = df1.merge(df2[['a', 'b', 'key1']], how = 'left',
                left_on = 'key2', right_on = 'key1').drop('key1')

The .drop('key1') part will prevent 'key1' from being kept in the resulting data frame, despite it being required to join in the first place.

Makefile - missing separator

You need to precede the lines starting with gcc and rm with a hard tab. Commands in make rules are required to start with a tab (unless they follow a semicolon on the same line). The result should look like this:

PROG = semsearch
all: $(PROG)
%: %.c
        gcc -o $@ $< -lpthread

        rm $(PROG)

Note that some editors may be configured to insert a sequence of spaces instead of a hard tab. If there are spaces at the start of these lines you'll also see the "missing separator" error. If you do have problems inserting hard tabs, use the semicolon way:

PROG = semsearch
all: $(PROG)
%: %.c ; gcc -o $@ $< -lpthread

clean: ; rm $(PROG)

How to export a Hive table into a CSV file?

There are ways to change the default delimiter, as shown by other answers.

There are also ways to convert the raw output to csv with some bash scripting. There are 3 delimiters to consider though, not just \001. Things get a bit more complicated when your hive table has maps.

I wrote a bash script that can handle all 3 default delimiters (\001 \002 and \003) from hive and output a csv. The script and some more info are here:

Hive Default Delimiters to CSV

Hive's default delimiters are

Row Delimiter => Control-A ('\001')
Collection Item Delimiter => Control-B ('\002')
Map Key Delimiter => Control-C ('\003')

There are ways to change these delimiters when exporting tables but sometimes you might still get stuck needing to convert this to csv.

Here's a quick bash script that can handle a DB export that's segmented in multiple files and has the default delimiters. It will output a single CSV file.

It is assumed that the segments all have the naming convention 000*_0

for f in $INDIRECTORY/000*_0; do 
  echo "Processing $f file.."; 
  cat -v $f | 
      LC_ALL=C sed -e "s/^/\"/g" | 
      LC_ALL=C sed -e "s/\^A/\",\"/g" | 
      LC_ALL=C sed -e "s/\^C\^B/\"\":\"\"\"\",\"\"/g" | 
      LC_ALL=C sed -e "s/\^B/\"\",\"\"/g" |  
      LC_ALL=C sed -e "s/\^C/\"\":\"\"/g" | 
      LC_ALL=C sed -e "s/$/\"/g" > $f-temp
echo "you,can,echo,your,header,here,if,you,like" > $INDIRECTORY/final_output.csv
cat $INDIRECTORY/*-temp >> $INDIRECTORY/final_output.csv
rm $INDIRECTORY/*-temp

More explanation on the gist

submitting a form when a checkbox is checked

I've been messing around with this for about four hours and decided to share this with you.

You can submit a form by clicking a checkbox but the weird thing is that when checking for the submission in php, you would expect the form to be set when you either check or uncheck the checkbox. But this is not true. The form only gets set when you actually check the checkbox, if you uncheck it it won't be set. the word checked at the end of a checkbox input type will cause the checkbox to display checked, so if your field is checked it will have to reflect that like in the example below. When it gets unchecked the php updates the field state which will cause the word checked the disappear.

You HTML should look like this:

<form method='post' action='#'>
<input type='checkbox' name='checkbox' onChange='submit();'
<?php if($page->checkbox_state == 1) { echo 'checked' }; ?>>

and the php:

if(isset($_POST['checkbox'])) {
   // the checkbox has just been checked 
   // save the new state of the checkbox somewhere
   $page->checkbox_state == 1;
} else {
   // the checkbox has just been unchecked
   // if you have another form ont the page which uses than you should
   // make sure that is not the one thats causing the page to handle in input
   // otherwise the submission of the other form will uncheck your checkbox
   // so this this line is optional:
      if(!isset($_POST['submit'])) {
          $page->checkbox_state == 0;

HTML how to clear input using javascript?

You could use a placeholder because it does it for you, but for old browsers that don't support placeholder, try this:

function clearThis(target) {
    if (target.value == "[email protected]") {
        target.value = "";
function replace(target) {
    if (target.value == "" || target.value == null) {
        target.value == "[email protected]";
<input type="text" name="email" value="[email protected]" size="x" onfocus="clearThis(this)" onblur="replace(this)" />

CODE EXPLAINED: When the text box has focus, clear the value. When text box is not focused AND when the box is blank, replace the value.

I hope that works, I have been having the same issue, but then I tried this and it worked for me.

Not able to start Genymotion device

(Windows 8) In my case i have changed default RAM from 1GB to 2GB on Genymotion and it gave this error. When i changed it back to 1GB it worked.

Reversing an Array in Java

The following will reverse in place the array between indexes i and j (to reverse the whole array call reverse(a, 0, a.length - 1))

    public void reverse(int[] a, int i , int j) {
        int ii =  i;
        int jj = j;

        while (ii < jj) {
            swap(ii, jj);

How can I divide one column of a data frame through another?

Hadley Wickham


packages is always a saver in case of data wrangling. To add the desired division as a third variable I would use mutate()

d <- mutate(d, new = min / count2.freq)

Git update submodules recursively

The way I use is:

git submodule update --init --recursive
git submodule foreach --recursive git fetch
git submodule foreach git merge origin master

How to check if a MySQL query using the legacy API was successful?

You can use mysql_errno() for this too.

$result = mysql_query($query);

    echo "MySQL error ".mysql_errno().": "
         .mysql_error()."\n<br>When executing <br>\n$query\n<br>";

Preventing form resubmission

Well I found nobody mentioned this trick.

Without redirection, you can still prevent the form confirmation when refresh.

By default, form code is like this:

<form method="post" action="test.php">

now, change it to <form method="post" action="test.php?nonsense=1">

You will see the magic.

I guess its because browsers won't trigger the confirmation alert popup if it gets a GET method (query string) in the url.

What does AngularJS do better than jQuery?


You go around making your webpage, and keep on putting {{data bindings}} whenever you feel you would have dynamic data. Angular will then provide you a $scope handler, which you can populate (statically or through calls to the web server).

This is a good understanding of data-binding. I think you've got that down.

DOM Manipulation

For simple DOM manipulation, which doesnot involve data manipulation (eg: color changes on mousehover, hiding/showing elements on click), jQuery or old-school js is sufficient and cleaner. This assumes that the model in angular's mvc is anything that reflects data on the page, and hence, css properties like color, display/hide, etc changes dont affect the model.

I can see your point here about "simple" DOM manipulation being cleaner, but only rarely and it would have to be really "simple". I think DOM manipulation is one the areas, just like data-binding, where Angular really shines. Understanding this will also help you see how Angular considers its views.

I'll start by comparing the Angular way with a vanilla js approach to DOM manipulation. Traditionally, we think of HTML as not "doing" anything and write it as such. So, inline js, like "onclick", etc are bad practice because they put the "doing" in the context of HTML, which doesn't "do". Angular flips that concept on its head. As you're writing your view, you think of HTML as being able to "do" lots of things. This capability is abstracted away in angular directives, but if they already exist or you have written them, you don't have to consider "how" it is done, you just use the power made available to you in this "augmented" HTML that angular allows you to use. This also means that ALL of your view logic is truly contained in the view, not in your javascript files. Again, the reasoning is that the directives written in your javascript files could be considered to be increasing the capability of HTML, so you let the DOM worry about manipulating itself (so to speak). I'll demonstrate with a simple example.

This is the markup we want to use. I gave it an intuitive name.

<div rotate-on-click="45"></div>

First, I'd just like to comment that if we've given our HTML this functionality via a custom Angular Directive, we're already done. That's a breath of fresh air. More on that in a moment.

Implementation with jQuery

live demo here (click).

function rotate(deg, elem) {
    webkitTransform: 'rotate('+deg+'deg)', 
    mozTransform: 'rotate('+deg+'deg)', 
    msTransform: 'rotate('+deg+'deg)', 
    oTransform: 'rotate('+deg+'deg)', 
    transform: 'rotate('+deg+'deg)'    

function addRotateOnClick($elems) {
  $elems.each(function(i, elem) {
    var deg = 0;
    $(elem).click(function() {
      deg+= parseInt($(this).attr('rotate-on-click'), 10);
      rotate(deg, this);


Implementation with Angular

live demo here (click).

app.directive('rotateOnClick', function() {
  return {
    restrict: 'A',
    link: function(scope, element, attrs) {
      var deg = 0;
      element.bind('click', function() {
        deg+= parseInt(attrs.rotateOnClick, 10);
          webkitTransform: 'rotate('+deg+'deg)', 
          mozTransform: 'rotate('+deg+'deg)', 
          msTransform: 'rotate('+deg+'deg)', 
          oTransform: 'rotate('+deg+'deg)', 
          transform: 'rotate('+deg+'deg)'    

Pretty light, VERY clean and that's just a simple manipulation! In my opinion, the angular approach wins in all regards, especially how the functionality is abstracted away and the dom manipulation is declared in the DOM. The functionality is hooked onto the element via an html attribute, so there is no need to query the DOM via a selector, and we've got two nice closures - one closure for the directive factory where variables are shared across all usages of the directive, and one closure for each usage of the directive in the link function (or compile function).

Two-way data binding and directives for DOM manipulation are only the start of what makes Angular awesome. Angular promotes all code being modular, reusable, and easily testable and also includes a single-page app routing system. It is important to note that jQuery is a library of commonly needed convenience/cross-browser methods, but Angular is a full featured framework for creating single page apps. The angular script actually includes its own "lite" version of jQuery so that some of the most essential methods are available. Therefore, you could argue that using Angular IS using jQuery (lightly), but Angular provides much more "magic" to help you in the process of creating apps.

This is a great post for more related information: How do I “think in AngularJS” if I have a jQuery background?

General differences.

The above points are aimed at the OP's specific concerns. I'll also give an overview of the other important differences. I suggest doing additional reading about each topic as well.

Angular and jQuery can't reasonably be compared.

Angular is a framework, jQuery is a library. Frameworks have their place and libraries have their place. However, there is no question that a good framework has more power in writing an application than a library. That's exactly the point of a framework. You're welcome to write your code in plain JS, or you can add in a library of common functions, or you can add a framework to drastically reduce the code you need to accomplish most things. Therefore, a more appropriate question is:

Why use a framework?

Good frameworks can help architect your code so that it is modular (therefore reusable), DRY, readable, performant and secure. jQuery is not a framework, so it doesn't help in these regards. We've all seen the typical walls of jQuery spaghetti code. This isn't jQuery's fault - it's the fault of developers that don't know how to architect code. However, if the devs did know how to architect code, they would end up writing some kind of minimal "framework" to provide the foundation (achitecture, etc) I discussed a moment ago, or they would add something in. For example, you might add RequireJS to act as part of your framework for writing good code.

Here are some things that modern frameworks are providing:

  • Templating
  • Data-binding
  • routing (single page app)
  • clean, modular, reusable architecture
  • security
  • additional functions/features for convenience

Before I further discuss Angular, I'd like to point out that Angular isn't the only one of its kind. Durandal, for example, is a framework built on top of jQuery, Knockout, and RequireJS. Again, jQuery cannot, by itself, provide what Knockout, RequireJS, and the whole framework built on top them can. It's just not comparable.

If you need to destroy a planet and you have a Death Star, use the Death star.

Angular (revisited).

Building on my previous points about what frameworks provide, I'd like to commend the way that Angular provides them and try to clarify why this is matter of factually superior to jQuery alone.

DOM reference.

In my above example, it is just absolutely unavoidable that jQuery has to hook onto the DOM in order to provide functionality. That means that the view (html) is concerned about functionality (because it is labeled with some kind of identifier - like "image slider") and JavaScript is concerned about providing that functionality. Angular eliminates that concept via abstraction. Properly written code with Angular means that the view is able to declare its own behavior. If I want to display a clock:



Yes, we need to go to JavaScript to make that mean something, but we're doing this in the opposite way of the jQuery approach. Our Angular directive (which is in it's own little world) has "augumented" the html and the html hooks the functionality into itself.

MVW Architecure / Modules / Dependency Injection

Angular gives you a straightforward way to structure your code. View things belong in the view (html), augmented view functionality belongs in directives, other logic (like ajax calls) and functions belong in services, and the connection of services and logic to the view belongs in controllers. There are some other angular components as well that help deal with configuration and modification of services, etc. Any functionality you create is automatically available anywhere you need it via the Injector subsystem which takes care of Dependency Injection throughout the application. When writing an application (module), I break it up into other reusable modules, each with their own reusable components, and then include them in the bigger project. Once you solve a problem with Angular, you've automatically solved it in a way that is useful and structured for reuse in the future and easily included in the next project. A HUGE bonus to all of this is that your code will be much easier to test.

It isn't easy to make things "work" in Angular.

THANK GOODNESS. The aforementioned jQuery spaghetti code resulted from a dev that made something "work" and then moved on. You can write bad Angular code, but it's much more difficult to do so, because Angular will fight you about it. This means that you have to take advantage (at least somewhat) to the clean architecture it provides. In other words, it's harder to write bad code with Angular, but more convenient to write clean code.

Angular is far from perfect. The web development world is always growing and changing and there are new and better ways being put forth to solve problems. Facebook's React and Flux, for example, have some great advantages over Angular, but come with their own drawbacks. Nothing's perfect, but Angular has been and is still awesome for now. Just as jQuery once helped the web world move forward, so has Angular, and so will many to come.

Where can I view Tomcat log files in Eclipse?

Another forum provided this answer:

Ahh, figured this out. The following system properties need to be set, so that the "" file can be picked up.

Assuming that the tomcat is located under an Eclipse project, add the following under the "Arguments" tab of its launch configuration:


PHP Fatal error: Cannot redeclare class

This function will print a stack telling you where it was called from:

function PrintTrace() {
    $trace = debug_backtrace();
    echo '<pre>';
    $sb = array();
    foreach($trace as $item) {
        if(isset($item['file'])) {
            $sb[] = htmlspecialchars("$item[file]:$item[line]");
        } else {
            $sb[] = htmlspecialchars("$item[class]:$item[function]");
    echo implode("\n",$sb);
    echo '</pre>';

Call this function at the top of the file that includes your class.

Sometimes it will only print once, even though your class is being included two or more times. This is because PHP actually parses all the top-level classes in a file before executing any code and throws the fatal error immediately. To remedy this, wrap your class declaration in if(true) { ... }, which will move your class down a level in scope. Then you should get your two traces before PHP fatal errors.

This should help you find where you class is being included from multiple times in a complex project.

Xcode 4: How do you view the console?

Here' an alternative

In Xcode 4 short cut to display and hide console is (command-shift-Y) , this will show the console and debugger below ur text edior in the same window.

What's the difference between "Request Payload" vs "Form Data" as seen in Chrome dev tools Network tab

The Request Payload - or to be more precise: payload body of a HTTP Request - is the data normally send by a POST or PUT Request. It's the part after the headers and the CRLF of a HTTP Request.

A request with Content-Type: application/json may look like this:

POST /some-path HTTP/1.1
Content-Type: application/json

{ "foo" : "bar", "name" : "John" }

If you submit this per AJAX the browser simply shows you what it is submitting as payload body. That’s all it can do because it has no idea where the data is coming from.

If you submit a HTML-Form with method="POST" and Content-Type: application/x-www-form-urlencoded or Content-Type: multipart/form-data your request may look like this:

POST /some-path HTTP/1.1
Content-Type: application/x-www-form-urlencoded


In this case the form-data is the request payload. Here the Browser knows more: it knows that bar is the value of the input-field foo of the submitted form. And that’s what it is showing to you.

So, they differ in the Content-Type but not in the way data is submitted. In both cases the data is in the message-body. And Chrome distinguishes how the data is presented to you in the Developer Tools.