Programs & Examples On #File type

The type of a file, as characterized by the format of the data it contains, or its use case. Specifies how bits are used to encode information.

How to have jQuery restrict file types on upload?

    $("input[name='btnsubmit']").attr('disabled', true);
    $('input[name="filphoto"]').change(function () {
    var ext = this.value.match(/\.(.+)$/)[1];
    switch (ext) 
    case 'jpg':
    case 'jpeg':
    case 'png':
    case 'bmp':
        $("input[name='btnsubmit']").attr('disabled', false);
        alert('This is not an allowed file type.');
        $("input[name='btnsubmit']").attr('disabled', true);
        this.value = '';

What do .c and .h file extensions mean to C?

The .c files are source files which will be compiled. The .h files are used to expose the API of a program to either other part of that program or other program is you are creating a library.

For example, the program PizzaDelivery could have 1 .c file with the main program, and 1 .c file with utility functions. Now, for the main part of the program to be able to use the utility functions, you need to expose the API, via function prototype, into a .h file, this .h file being included by the main .c file.

Full path from file input using jQuery

You can't: It's a security feature in all modern browsers.

For IE8, it's off by default, but can be reactivated using a security setting:

When a file is selected by using the input type=file object, the value of the value property depends on the value of the "Include local directory path when uploading files to a server" security setting for the security zone used to display the Web page containing the input object.

The fully qualified filename of the selected file is returned only when this setting is enabled. When the setting is disabled, Internet Explorer 8 replaces the local drive and directory path with the string C:\fakepath\ in order to prevent inappropriate information disclosure.

In all other current mainstream browsers I know of, it is also turned off. The file name is the best you can get.

More detailed info and good links in this question. It refers to getting the value server-side, but the issue is the same in JavaScript before the form's submission.

Upload DOC or PDF using PHP


    //create table


    -- Database: `mydb`

    -- --------------------------------------------------------

    -- Table structure for table `tbl_user_data`

    CREATE TABLE `tbl_user_data` (
      `attachment_id` int(11) NOT NULL,
      `attachment` varchar(200) NOT NULL

    -- Indexes for dumped tables

    -- Indexes for table `tbl_user_data`
    ALTER TABLE `tbl_user_data`
      ADD PRIMARY KEY (`attachment_id`);

    -- AUTO_INCREMENT for dumped tables

    -- AUTO_INCREMENT for table `tbl_user_data`
    ALTER TABLE `tbl_user_data`
      MODIFY `attachment_id` int(11) NOT NULL AUTO_INCREMENT;

    $servername = "localhost";
    $username = "root";
    $password = "";
    // Create connection
    $dbname = "myDB";
    // Create connection
    $conn = new mysqli($servername, $username, $password, $dbname);
    // Check connection
    if ($conn->connect_error) {
        die("Connection failed: " . $conn->connect_error);


      $statusMsg = '';

      //file upload path
      $targetDir = "resumeUpload/";
      $fileName = basename($_FILES["resume"]["name"]);
      $targetFilePath = $targetDir . $newFileName;
      $fileType = pathinfo($targetFilePath,PATHINFO_EXTENSION);

      if(!empty($_FILES["resume"]["name"])) {
          //allow certain file formats
          //$allowTypes = array('jpg','png','jpeg','gif','pdf','docx','doc');
          $allowTypes = array('pdf','docx','doc');
          if(in_array($fileType, $allowTypes)){
              //upload file to server
              if(move_uploaded_file($_FILES["resume"]["tmp_name"], $targetFilePath)){
                  $statusMsg = "The file ".$fileName. " has been uploaded.";
                  $statusMsg = "Sorry, there was an error uploading your file.";
              $statusMsg = 'Sorry, only DOC,DOCX, & PDF files are allowed to upload.';
          $statusMsg = 'Please select a file to upload.';

      //display status message
      echo $statusMsg;

      $sql="INSERT INTO `tbl_user_data` (`attachment_id`, `attachment`) VALUES
      ('NULL', '$newFileName')";

      if (mysqli_query($conn, $sql)) {

       $last_id = mysqli_insert_id($conn);
         echo "upload success";
      } else {
          echo "Error: " . $sql . "<br>" . mysqli_error($conn);


    <form id="frm_upload" action="" method="post" enctype="multipart/form-data">
    Upload Resume:<input type="file" name="resume" id="resume">
    <button type="submit" name="submit">Apply  Now</button> 

     //output sample[![check here for sample output][1]][1]

Node.js get file extension

This solution supports querystrings!

var Url = require('url');
var Path = require('path');

var url = '';
var result = Path.extname(Url.parse(url).pathname); // '.jpg'

Get column from a two dimensional array

I have created a library matrix-slicer to manipulate with matrix items. So your problem could be solved like this:

var m = new Matrix([
    [1, 2],
    [3, 4],

m.getColumn(1); // => [2, 4]

Possible it will be useful for somebody. ;-)

Java string replace and the NUL (NULL, ASCII 0) character?

Should be probably changed to

firstName = firstName.trim().replaceAll("\\.", "");

How to rename a table in SQL Server?

To change a table name with a different schema:

Example: Change dbo.MyTable1 to wrk.MyTable2

EXEC SP_RENAME 'dbo.MyTable1', 'MyTable2'


What regular expression will match valid international phone numbers?

This will work for international numbers;


@"^((\+\d{1,3}(-| )?\(?\d\)?(-| )?\d{1,5})|(\(?\d{2,6}\)?))(-| )?(\d{3,4})(-| )?(\d{4})(( x| ext)\d{1,5}){0,1}$"


/^((\+\d{1,3}(-| )?\(?\d\)?(-| )?\d{1,5})|(\(?\d{2,6}\)?))(-| )?(\d{3,4})(-| )?(\d{4})(( x| ext)\d{1,5}){0,1}$/

Error message 'Unable to load one or more of the requested types. Retrieve the LoaderExceptions property for more information.'

Adding my specific problem/solution to this as this is the first result for this error message. In my case, the error was received when I deployed a second application within the folder of my first application in IIS. Both were defining connection string with the same name resulting in the child application having a conflict and in turn generating this (to me) non-obvious error message. It was solved by adding:


in the connection string block of the child web application which prevented it from inheriting the connection strings of web.config files higher in the hierarchy, so it looks like:

  <add name="DbContext" connectionString="MySERVER" providerName="System.Data.SqlClient" />

A reference Stack Overflow question which helped once I determined what was going on was Will a child application inherit from its parent web.config?.

Why can't C# interfaces contain fields?

The short answer is yes, every implementing type will have to create its own backing variable. This is because an interface is analogous to a contract. All it can do is specify particular publicly accessible pieces of code that an implementing type must make available; it cannot contain any code itself.

Consider this scenario using what you suggest:

public interface InterfaceOne
    int myBackingVariable;

    int MyProperty { get { return myBackingVariable; } }

public interface InterfaceTwo
    int myBackingVariable;

    int MyProperty { get { return myBackingVariable; } }

public class MyClass : InterfaceOne, InterfaceTwo { }

We have a couple of problems here:

  • Because all members of an interface are--by definition--public, our backing variable is now exposed to anyone using the interface
  • Which myBackingVariable will MyClass use?

The most common approach taken is to declare the interface and a barebones abstract class that implements it. This allows you the flexibility of either inheriting from the abstract class and getting the implementation for free, or explicitly implementing the interface and being allowed to inherit from another class. It works something like this:

public interface IMyInterface
    int MyProperty { get; set; }

public abstract class MyInterfaceBase : IMyInterface
    int myProperty;

    public int MyProperty
        get { return myProperty; }
        set { myProperty = value; }

Column/Vertical selection with Keyboard in SublimeText 3

This should do it:

  1. Ctrl+A - select all.
  2. Ctrl+Shift+L - split selection into lines.
  3. Then move all cursors with left/right, select with Shift+left/right. Move all cursors to start of line with Home.

A message body writer for Java type, class myPackage.B, and MIME media type, application/octet-stream, was not found

In your client code you are not specifying the content type of the data you are sending - so Jersey is not able to locate the right MessageBodyWritter to serialize the b1 object.

Modify the last line of your main method as follows:

ClientResponse response = resource.type(MediaType.APPLICATION_XML).put(ClientResponse.class, b1);

And add @XmlRootElement annotation to class B on both the server as well as the client sides.

How to pass an object into a state using UI-router?

Btw you can also use the ui-sref attribute in your templates to pass objects

ui-sref="myState({ myParam: myObject })"

SQL Server - inner join when updating

This should do it:

UPDATE ProductReviews
SET    ProductReviews.status = '0'
FROM   ProductReviews
       INNER JOIN products
         ON =
WHERE = '17190'
       AND products.shopkeeper = '89137'

How to update a plot in matplotlib?

This worked for me. Repeatedly calls a function updating the graph every time.

import matplotlib.pyplot as plt
import matplotlib.animation as anim

def plot_cont(fun, xmax):
    y = []
    fig = plt.figure()
    ax = fig.add_subplot(1,1,1)

    def update(i):
        yi = fun()
        x = range(len(y))
        ax.plot(x, y)
        print i, ': ', yi

    a = anim.FuncAnimation(fig, update, frames=xmax, repeat=False)

"fun" is a function that returns an integer. FuncAnimation will repeatedly call "update", it will do that "xmax" times.

How to position the div popup dialog to the center of browser screen?

I think you need to make the .holder position:relative; and .popup position:absolute;

How do I split a string on a delimiter in Bash?

There are two simple methods:

cat "text1;text2;text3" | tr " " "\n"


cat "text1;text2;text3" | sed -e 's/ /\n/g'

ReactJS - Get Height of an element

See this fiddle (actually updated your's)

You need to hook into componentDidMount which is run after render method. There, you get actual height of element.

var DivSize = React.createClass({
    getInitialState() {
    return { state: 0 };

  componentDidMount() {
    const height = document.getElementById('container').clientHeight;
    this.setState({ height });

  render: function() {
    return (
        <div className="test">
        Size: <b>{this.state.height}px</b> but it should be 18px after the render

  <DivSize />,
<script src=""></script>

<div id="container">
jhiwhiw (this is 36px height)
    <!-- This element's contents will be replaced with your component. -->

How to add an ORDER BY clause using CodeIgniter's Active Record methods?

I believe the get() function immediately runs the select query and does not accept ORDER BY conditions as parameters. I think you'll need to separately declare the conditions, then run the query. Give this a try:

$this->db->order_by("name", "asc");
$query = $this->db->get(); 
return $query->result();

CodeIgniter Documentation order_by()

How to fix a header on scroll

I know Coop has already answered this question, but here is a version which also tracks where in the document the div is, rather than relying on a static value:


var offset = $( ".sticky-header" ).offset();
var sticky = document.getElementById("sticky-header")

$(window).scroll(function() {

    if ( $('body').scrollTop() >{
    } else {



     position: fixed;
    top: 0px;

What is the advantage of using heredoc in PHP?

Heredoc's are a great alternative to quoted strings because of increased readability and maintainability. You don't have to escape quotes and (good) IDEs or text editors will use the proper syntax highlighting.

A very common example: echoing out HTML from within PHP:

$html = <<<HTML
  <div class='something'>
    <ul class='mylist'>

// Sometime later
echo $html;

It is easy to read and easy to maintain.

The alternative is echoing quoted strings, which end up containing escaped quotes and IDEs aren't going to highlight the syntax for that language, which leads to poor readability and more difficulty in maintenance.

Updated answer for Your Common Sense

Of course you wouldn't want to see an SQL query highlighted as HTML. To use other languages, simply change the language in the syntax:

$sql = <<<SQL
       SELECT * FROM table

How can I install a previous version of Python 3 in macOS using homebrew?

As an update, when doing

brew unlink python # If you have installed (with brew) another version of python
brew install

You may encounter

Error: python contains a recursive dependency on itself:
  python depends on sphinx-doc
  sphinx-doc depends on python

To bypass it, add the --ignore-dependencies argument to brew install.

brew unlink python # If you have installed (with brew) another version of python
brew install --ignore-dependencies

What data type to use for hashed password field and what length?

It really depends on the hashing algorithm you're using. The length of the password has little to do with the length of the hash, if I remember correctly. Look up the specs on the hashing algorithm you are using, run a few tests, and truncate just above that.

Batch Files - Error Handling

Using ERRORLEVEL when it's available is the easiest option. However, if you're calling an external program to perform some task, and it doesn't return proper codes, you can pipe the output to 'find' and check the errorlevel from that.

c:\mypath\myexe.exe | find "ERROR" >nul2>nul
if not ERRORLEVEL 1 (
echo. Uh oh, something bad happened
exit /b 1

Or to give more info about what happened

c:\mypath\myexe.exe 2&1> myexe.log
find "Invalid File" "myexe.log" >nul2>nul && echo.Invalid File error in Myexe.exe && exit /b 1
find "Error 0x12345678" "myexe.log" >nul2>nul && echo.Myexe.exe was unable to contact server x && exit /b 1

Why does AngularJS include an empty option in select?

A quick solution:

select option:empty { display:none }

Hope it helps someone. Ideally, the selected answer should be the approach but if in case that's not possible then should work as a patch.

How do you check for permissions to write to a directory or file?

Its a fixed version of MaxOvrdrv's Code.

public static bool IsReadable(this DirectoryInfo di)
    AuthorizationRuleCollection rules;
    WindowsIdentity identity;
        rules = di.GetAccessControl().GetAccessRules(true, true, typeof(SecurityIdentifier));
        identity = WindowsIdentity.GetCurrent();
    catch (UnauthorizedAccessException uae)
        return false;

    bool isAllow = false;
    string userSID = identity.User.Value;

    foreach (FileSystemAccessRule rule in rules)
        if (rule.IdentityReference.ToString() == userSID || identity.Groups.Contains(rule.IdentityReference))
            if ((rule.FileSystemRights.HasFlag(FileSystemRights.Read) ||
                rule.FileSystemRights.HasFlag(FileSystemRights.ReadAttributes) ||
                rule.FileSystemRights.HasFlag(FileSystemRights.ReadData)) && rule.AccessControlType == AccessControlType.Deny)
                return false;
            else if ((rule.FileSystemRights.HasFlag(FileSystemRights.Read) &&
                rule.FileSystemRights.HasFlag(FileSystemRights.ReadAttributes) &&
                rule.FileSystemRights.HasFlag(FileSystemRights.ReadData)) && rule.AccessControlType == AccessControlType.Allow)
                isAllow = true;

    return isAllow;

public static bool IsWriteable(this DirectoryInfo me)
    AuthorizationRuleCollection rules;
    WindowsIdentity identity;
        rules = me.GetAccessControl().GetAccessRules(true, true, typeof(System.Security.Principal.SecurityIdentifier));
        identity = WindowsIdentity.GetCurrent();
    catch (UnauthorizedAccessException uae)
        return false;

    bool isAllow = false;
    string userSID = identity.User.Value;

    foreach (FileSystemAccessRule rule in rules)
        if (rule.IdentityReference.ToString() == userSID || identity.Groups.Contains(rule.IdentityReference))
            if ((rule.FileSystemRights.HasFlag(FileSystemRights.Write) ||
                rule.FileSystemRights.HasFlag(FileSystemRights.WriteAttributes) ||
                rule.FileSystemRights.HasFlag(FileSystemRights.WriteData) ||
                rule.FileSystemRights.HasFlag(FileSystemRights.CreateDirectories) ||
                rule.FileSystemRights.HasFlag(FileSystemRights.CreateFiles)) && rule.AccessControlType == AccessControlType.Deny)
                return false;
            else if ((rule.FileSystemRights.HasFlag(FileSystemRights.Write) &&
                rule.FileSystemRights.HasFlag(FileSystemRights.WriteAttributes) &&
                rule.FileSystemRights.HasFlag(FileSystemRights.WriteData) &&
                rule.FileSystemRights.HasFlag(FileSystemRights.CreateDirectories) &&
                rule.FileSystemRights.HasFlag(FileSystemRights.CreateFiles)) && rule.AccessControlType == AccessControlType.Allow)
                isAllow = true;

    return isAllow;

Android/Eclipse: how can I add an image in the res/drawable folder?

You just need to copy/cut and paste the images into drawable folder using windows/mac file explorer

To refresh the workspace follow the steps mentioned in this question Eclipse: How do i refresh an entire workspace? F5 doesn't do it

If that does not work you might wanna restart eclispe

How to input a string from user into environment variable from batch file

You can use set with the /p argument:

SET /P variable=[promptString]

The /P switch allows you to set the value of a variable to a line of input entered by the user. Displays the specified promptString before reading the line of input. The promptString can be empty.

So, simply use something like

set /p Input=Enter some text: 

Later you can use that variable as argument to a command:

myCommand %Input%

Be careful though, that if your input might contain spaces it's probably a good idea to quote it:

myCommand "%Input%"

How to update PATH variable permanently from Windows command line?

This script

includes all the necessary Windows API calls which can be refactored for your needs. It is actually an AutoHotkey GUI to change the System PATH easily. Needs to be run as an Administrator.

Sending mass email using PHP

I would insert all the emails into a database (sort of like a queue), then process them one at a time as you have done in your code (if you want to use swiftmailer or phpmailer etc, you can do that too.)

After each mail is sent, update the database to record the date/time it was sent.

By putting them in the database first you have

  1. a record of who you sent it to
  2. if your script times out or fails and you have to run it again, then you won't end up sending the same email out to people twice
  3. you can run the send process from a cron job and do a batch at a time, so that your mail server is not overwhelmed, and keep track of what has been sent

Keep in mind, how to automate bounced emails or invalid emails so they can automatically removed from your list.

If you are sending that many emails you are bound to get a few bounces.

Why does this code using random strings print "hello world"?

It's all about the input seed. Same seed give the same results all the time. Even you re-run your program again and again it's the same output.

public static void main(String[] args) {



private static void randomString(int i) {
    Random ran = new Random(i);




lambda expression join multiple tables with select and where clause

If I understand your questions correctly, all you need to do is add the .Where(m => m.r.u.UserId == 1):

    var UserInRole = db.UserProfiles.
        Join(db.UsersInRoles, u => u.UserId, uir => uir.UserId,
        (u, uir) => new { u, uir }).
        Join(db.Roles, r => r.uir.RoleId, ro => ro.RoleId, (r, ro) => new { r, ro })
        .Where(m => m.r.u.UserId == 1)
        .Select (m => new AddUserToRole
            UserName = m.r.u.UserName,
            RoleName =

Hope that helps.

Try-catch block in Jenkins pipeline script

You're using the declarative style of specifying your pipeline, so you must not use try/catch blocks (which are for Scripted Pipelines), but the post section. See:

How to print variables in Perl

You should always include all relevant code when asking a question. In this case, the print statement that is the center of your question. The print statement is probably the most crucial piece of information. The second most crucial piece of information is the error, which you also did not include. Next time, include both of those.

print $ids should be a fairly hard statement to mess up, but it is possible. Possible reasons:

  1. $ids is undefined. Gives the warning undefined value in print
  2. $ids is out of scope. With use strict, gives fatal warning Global variable $ids needs explicit package name, and otherwise the undefined warning from above.
  3. You forgot a semi-colon at the end of the line.
  4. You tried to do print $ids $nIds, in which case perl thinks that $ids is supposed to be a filehandle, and you get an error such as print to unopened filehandle.


1: Should not happen. It might happen if you do something like this (assuming you are not using strict):

my $var;
while (<>) {
    $Var .= $_;
print $var;

Gives the warning for undefined value, because $Var and $var are two different variables.

2: Might happen, if you do something like this:

if ($something) {
    my $var = "something happened!";
print $var;

my declares the variable inside the current block. Outside the block, it is out of scope.

3: Simple enough, common mistake, easily fixed. Easier to spot with use warnings.

4: Also a common mistake. There are a number of ways to correctly print two variables in the same print statement:

print "$var1 $var2";  # concatenation inside a double quoted string
print $var1 . $var2;  # concatenation
print $var1, $var2;   # supplying print with a list of args

Lastly, some perl magic tips for you:

use strict;
use warnings;

# open with explicit direction '<', check the return value
# to make sure open succeeded. Using a lexical filehandle.
open my $fh, '<', 'file.txt' or die $!;

# read the whole file into an array and
# chomp all the lines at once
chomp(my @file = <$fh>);
close $fh;

my $ids  = join(' ', @file);
my $nIds = scalar @file;
print "Number of lines: $nIds\n";
print "Text:\n$ids\n";

Reading the whole file into an array is suitable for small files only, otherwise it uses a lot of memory. Usually, line-by-line is preferred.


  • print "@file" is equivalent to $ids = join(' ',@file); print $ids;
  • $#file will return the last index in @file. Since arrays usually start at 0, $#file + 1 is equivalent to scalar @file.

You can also do:

my $ids;
do {
    local $/;
    $ids = <$fh>;

By temporarily "turning off" $/, the input record separator, i.e. newline, you will make <$fh> return the entire file. What <$fh> really does is read until it finds $/, then return that string. Note that this will preserve the newlines in $ids.

Line-by-line solution:

open my $fh, '<', 'file.txt' or die $!; # btw, $! contains the most recent error
my $ids;
while (<$fh>) {
    $ids .= "$_ "; # concatenate with string
my $nIds = $.; # $. is Current line number for the last filehandle accessed.

Floating point exception

This should give you a really good idea. Since a modulus is, in its basic sense, division with a remainder, something % 0 IS division by zero and as such, will trigger a SIGFPE being thrown.

I can't install python-ldap

python3 does not support python-ldap. Rather to install ldap3.

How to determine the screen width in terms of dp or dip at runtime in Android?

This is a copy/pastable function to be used based on the previous responses.

     * @param context
     * @return the Screen height in DP
    public static float getHeightDp(Context context) {
        DisplayMetrics displayMetrics = context.getResources().getDisplayMetrics();
        float dpHeight = displayMetrics.heightPixels / displayMetrics.density;
        return dpHeight;

     * @param context
     * @return the screnn width in dp
    public static float getWidthDp(Context context) {
        DisplayMetrics displayMetrics = context.getResources().getDisplayMetrics();
        float dpWidth = displayMetrics.widthPixels / displayMetrics.density;
        return dpWidth;

Replace Line Breaks in a String C#

var answer = Regex.Replace(value, "(\n|\r)+", replacementString);

How do I format currencies in a Vue component?

The comment by @RoyJ has a great suggestion. In the template you can just use built-in localized strings:

     Total: <b>{{ }}</b>

It's not supported in some of the older browsers, but if you're targeting IE 11 and later, you should be fine.

How to change the timeout on a .NET WebClient object

You can extend the timeout: inherit the original WebClient class and override the webrequest getter to set your own timeout, like in the following example.

MyWebClient was a private class in my case:

private class MyWebClient : WebClient
    protected override WebRequest GetWebRequest(Uri uri)
        WebRequest w = base.GetWebRequest(uri);
        w.Timeout = 20 * 60 * 1000;
        return w;

Easiest way to use SVG in Android?

Android Studio supports SVG from 1.4 onwards

Here is a video on how to import.

Size of character ('a') in C/C++

In C, the type of a character constant like 'a' is actually an int, with size of 4 (or some other implementation-dependent value). In C++, the type is char, with size of 1. This is one of many small differences between the two languages.

How to calculate a Mod b in Casio fx-991ES calculator

You can calculate A mod B (for positive numbers) using this:

Pol( -Rec( 1/r , 2πr × A/B ) , Y ) ( πr - Y ) B

Then press [CALC], and enter your values for A and B, and any value for Y.

/ indicates using the fraction key, and r means radians ( [SHIFT] [Ans] [2] )

html/css buttons that scroll down to different div sections on a webpage


<a href="#top">Top</a>
<a href="#middle">Middle</a>
<a href="#bottom">Bottom</a>
<div id="top"><a href="top"></a>Top</div>
<div id="middle"><a href="middle"></a>Middle</div>
<div id="bottom"><a href="bottom"></a>Bottom</div>


    height: 600px;
    width: 300px;
    background: green; 


Google Maps API v3: How do I dynamically change the marker icon?

This thread might be dead, but StyledMarker is available for API v3. Just bind the color change you want to the correct DOM event using the addDomListener() method. This example is pretty close to what you want to do. If you look at the page source, change:

google.maps.event.addDomListener(document.getElementById("changeButton"),"click",function() {

to something like:

google.maps.event.addDomListener("mouseover",function() {

That should be enough to get you moving along.

The Wikipedia page on DOM Events will also help you target the event that you want to capture on the client-side.

Good luck (if you still need it)

How do I make an attributed string using Swift?


  • Swift 5.2, Xcode 11.4 (11E146)


protocol AttributedStringComponent {
    var text: String { get }
    func getAttributes() -> [NSAttributedString.Key: Any]?

// MARK: String extensions

extension String: AttributedStringComponent {
    var text: String { self }
    func getAttributes() -> [NSAttributedString.Key: Any]? { return nil }

extension String {
    func toAttributed(with attributes: [NSAttributedString.Key: Any]?) -> NSAttributedString {
        .init(string: self, attributes: attributes)

// MARK: NSAttributedString extensions

extension NSAttributedString: AttributedStringComponent {
    var text: String { string }

    func getAttributes() -> [Key: Any]? {
        if string.isEmpty { return nil }
        var range = NSRange(location: 0, length: string.count)
        return attributes(at: 0, effectiveRange: &range)

extension NSAttributedString {

    convenience init?(from attributedStringComponents: [AttributedStringComponent],
                      defaultAttributes: [NSAttributedString.Key: Any],
                      joinedSeparator: String = " ") {
        switch attributedStringComponents.count {
        case 0: return nil
            var joinedString = ""
            typealias SttributedStringComponentDescriptor = ([NSAttributedString.Key: Any], NSRange)
            let sttributedStringComponents = attributedStringComponents.enumerated().flatMap { (index, component) -> [SttributedStringComponentDescriptor] in
                var components = [SttributedStringComponentDescriptor]()
                if index != 0 {
                                       NSRange(location: joinedString.count, length: joinedSeparator.count)))
                    joinedString += joinedSeparator
                components.append((component.getAttributes() ?? defaultAttributes,
                                   NSRange(location: joinedString.count, length: component.text.count)))
                joinedString += component.text
                return components

            let attributedString = NSMutableAttributedString(string: joinedString)
            sttributedStringComponents.forEach { attributedString.addAttributes($0, range: $1) }
            self.init(attributedString: attributedString)


let defaultAttributes = [
    .font: UIFont.systemFont(ofSize: 16, weight: .regular),
] as [NSAttributedString.Key : Any]

let marketingAttributes = [
    .font: UIFont.systemFont(ofSize: 20.0, weight: .bold),
] as [NSAttributedString.Key : Any]

let attributedStringComponents = [
    "pay for",
    NSAttributedString(string: "one",
                       attributes: marketingAttributes),
    "and get",
    "three!\n".toAttributed(with: marketingAttributes),
    "Only today!".toAttributed(with: [
        .font: UIFont.systemFont(ofSize: 16.0, weight: .bold),
] as [AttributedStringComponent]
let attributedText = NSAttributedString(from: attributedStringComponents, defaultAttributes: defaultAttributes)

Full Example

do not forget to paste the solution code here

import UIKit

class ViewController: UIViewController {

    private weak var label: UILabel!
    override func viewDidLoad() {
        let label = UILabel(frame: .init(x: 40, y: 40, width: 300, height: 80))
        label.numberOfLines = 2
        self.label = label

        let defaultAttributes = [
            .font: UIFont.systemFont(ofSize: 16, weight: .regular),
        ] as [NSAttributedString.Key : Any]

        let marketingAttributes = [
            .font: UIFont.systemFont(ofSize: 20.0, weight: .bold),
        ] as [NSAttributedString.Key : Any]

        let attributedStringComponents = [
            "pay for",
            NSAttributedString(string: "one",
                               attributes: marketingAttributes),
            "and get",
            "three!\n".toAttributed(with: marketingAttributes),
            "Only today!".toAttributed(with: [
                .font: UIFont.systemFont(ofSize: 16.0, weight: .bold),
        ] as [AttributedStringComponent]
        label.attributedText = NSAttributedString(from: attributedStringComponents, defaultAttributes: defaultAttributes)
        label.textAlignment = .center


enter image description here

How to create a function in SQL Server

This will work for most of the website names :

SELECT ID, REVERSE(PARSENAME(REVERSE(WebsiteName), 2)) FROM dbo.YourTable .....

What exactly is the meaning of an API?

An API is a set of commands, functions, and protocols which programmers can use when building software for a specific OS or any other software. The API allows programmers to use predefined functions to interact with the operating system, instead of writing them from scratch. All computer operating systems, such as Windows, Unix, and the Mac OS and language such as Java provide an application program interface for programmers.


Determine if a cell (value) is used in any formula

On Excel 2010 try this:

  1. select the cell you want to check if is used somewhere in a formula;
  2. Formulas -> Trace Dependents (on Formula Auditing menu)

Setting the default ssh key location

If you are only looking to point to a different location for you identity file, the you can modify your ~/.ssh/config file with the following entry:

IdentityFile ~/.foo/identity

man ssh_config to find other config options.

"cannot resolve symbol R" in Android Studio

To Fix "can not resolve symbol r" error. Try these solutions.

  1. Build -> Clean Project.

  2. Build -> Build Project.

  3. Build -> Make Project.
  4. Third icon from left in Toolbar -> Sync project with gradle files.
  5. File -> Invalidate caches and restart.
  6. Make sure you are using compatible gradle version in application level gradle file.

e.g. : "classpath ''".

I hope these solutions can help you.

Thanks for reading.

How to compile the finished C# project and then run outside Visual Studio?

The easiest way is:

  • Find the drop-down box at the top of Visual Studio's window that says Debug
  • Select Release
  • Hit F6 to build it
  • Switch back to Debug and then close Visual Studio
  • Open Windows Explorer and navigate to your project's folder (My Documents\Visual Studio 200x\Projects\my_project\)
  • Now go to bin\Release\ and copy the executable from there to wherever you want to store it
  • Make shortcuts as appropriate and enjoy your new game! :)

How to get rid of blank pages in PDF exported from SSRS

I've successfully used pdftk to remove pages I didn't want/need in pdfs. You can download the program here

You might try something like the following. Taken from here under examples

Remove 'page 13' from in1.pdf to create out1.pdf pdftk in.pdf cat 1-12 14-end output out1.pdf


pdftk A=in1.pdf cat A1-12 A14-end output out1.pdf

Choosing a file in Python with simple Dialog

With EasyGui:

import easygui

To install:

pip install easygui


import easygui

Add all files to a commit except a single file?

1) To start ignoring changes to a single already versioned file

git update-index --assume-unchanged "main/dontcheckmein.txt"

and to undo that git update-index --no-assume-unchanged "main/dontcheckmein.txt"

github docs to ignore files

2) To completely ignore a specific single file preventing it from being created at repository

First, look at this stackoverflow post: Git global ignore not working

In .gitignore, add the relative path to the file without leading ./.

So, if your file is at MyProject/MyFolder/myfile.txt, (where .git is also in the MyProject folder), add MyFolder/myfile.txt to your at .gitignore file.

You can confirm what rules are associated with ignore via git check-ignore "MyFolder/myfile.txt"

About global ignore

That link talks about ~/.gitignore_global, but the file is related to your project. So, if you put the exclude pattern MyFolder/myfile.txt in ~/.gitignore_global, it will work but will not make much sense...

On the other hand, if you setup your project with git config core.excludesfile .gitignore where .gitignore is in MyProject, the local file will override ~/.gitignore_global, which can have very useful rules...

So, for now, I think it's best to make some script to mix your .gitignore with ~/.gitignore_global at .gitignore.

One last warning
If the file you want to ignore is already in the repository, this method will not work unless you do this: git rm "MyFolder/myfile.txt", but back it up first, as it will be removed locally also! You can copy it back later...

How to convert a DataTable to a string in C#?

using(var writer = new StringWriter()) {

Of course the usefulness of this depends on how important the formatting is. If it's just a debug dump, I find XML outputs like this very readable. However, if the formatting is important to you, then you have no choice but to write your own method to do it.

Should you use rgba(0, 0, 0, 0) or rgba(255, 255, 255, 0) for transparency in CSS?

There a small difference when u use rgba(255,255,255,a),background color becomes more and more lighter as the value of 'a' increase from 0.0 to 1.0. Where as when use rgba(0,0,0,a), the background color becomes more and more darker as the value of 'a' increases from 0.0 to 1.0. Having said that, its clear that both (255,255,255,0) and (0,0,0,0) make background transparent. (255,255,255,1) would make the background completely white where as (0,0,0,1) would make background completely black.

Bootstrap modal not displaying

If you are using angular and trying to create a directive that has a custom modal in it, the modal backdrop will show but the modal itself will not unless you set replace: true on your directive.

Typescript Directive:

export class myModalDirective implements ng.IDirective {
    static Register = () => {
        angular.module('app').directive('myModal', () => { return new myModalDirective () });
    templateUrl = 'mymodal.html'    
restrict = 'E';
    replace = true;
    scope = {
        show: '='
    link = (scope: any, element: ng.IAugmentedJQuery, attrs: ng.IAttributes, ctrl: any) => {
        var vm = this;
        scope.$watch(function () { return; }, function (vis) {
            if (vis) {
            } else {

    constructor () {

Modal HTML

<div class="modal fade" data-keyboard="false" data-backdrop="static">
    <div class="modal-dialog">
        <div class="modal-content">
                <div class="modal-header">
                    <h4 class="modal-title">Modal Title</h4>
                <div class="modal-body">

close fancy box from function from within open 'fancybox'

Bit of an old thread but ...

Actually, I suspect that the answer to the original question about how to close the window from within the window has more to do with the fact that the click event is not attached to the element. If the click event is attached in document.ready the event will not be attached when fancybox creates the new window.

You need to re-apply the click event once the new window . Probably the easiest way to do this is to use onComplete feature.

This works for me:

    'transitionIn'  :   'fade',
    'transitionOut' :   'elastic',
    'speedIn'       :   600, 
    'speedOut'      :   400, 
    'overlayShow'   :   true,
    'overlayColor'  :   '#000022',
            'overlayOpacity'  : 0.8,
            'onComplete' : function(){$('.closer').click(function(){parent.$.fancybox.close();})}

Actually, after a bit of thought 'live' rather than 'click' or 'bind' might work just as well.

How can I force Python's file.write() to use the same newline format in Windows as in Linux ("\r\n" vs. "\n")?

You need to open the file in binary mode i.e. wb instead of w. If you don't, the end of line characters are auto-converted to OS specific ones.

Here is an excerpt from Python reference about open().

The default is to use text mode, which may convert '\n' characters to a platform-specific representation on writing and back on reading.

Is there a simple, elegant way to define singletons?

I think that forcing a class or an instance to be a singleton is overkill. Personally, I like to define a normal instantiable class, a semi-private reference, and a simple factory function.

class NothingSpecial:

_the_one_and_only = None

def TheOneAndOnly():
    global _the_one_and_only
    if not _the_one_and_only:
        _the_one_and_only = NothingSpecial()
    return _the_one_and_only

Or if there is no issue with instantiating when the module is first imported:

class NothingSpecial:

THE_ONE_AND_ONLY = NothingSpecial()

That way you can write tests against fresh instances without side effects, and there is no need for sprinkling the module with global statements, and if needed you can derive variants in the future.

Get all column names of a DataTable into string array using (LINQ/Predicate)

Try this (LINQ method syntax):

string[] columnNames = dt.Columns.Cast<DataColumn>()
                                 .Select(x => x.ColumnName)

or in LINQ Query syntax:

string[] columnNames = (from dc in dt.Columns.Cast<DataColumn>()
                        select dc.ColumnName).ToArray();

Cast is required, because Columns is of type DataColumnCollection which is a IEnumerable, not IEnumerable<DataColumn>. The other parts should be obvious.

How to fix "unable to write 'random state' " in openssl

Angular js init ng-model from default values

I tried what @Mark Rajcok suggested. Its working for String values (Visa-4242). Please refer this fiddle.

From the fiddle:

The same thing that is done in the fiddle can be done using ng-repeat, which everybody could recommend. But after reading the answer given by @Mark Rajcok, i just wanted to try the same for a form with array of profiles. Things work well untill i have the $scope.profiles = [{},{}]; code in the controller. If i remove this code, im getting errors. But in normal scenarios i cant print $scope.profiles = [{},{}]; as i print or echo html from the server. Will it be possible to execute the above, in a similar fashion as @Mark Rajcok did for the string values like <input name="card[description]" ng-model="card.description" ng-init="card.description='Visa-4242'">, without having to echo the JavaScript part from the server.

How to limit the number of selected checkboxes?

Working DEMO

Try this

var theCheckboxes = $(".pricing-levels-3 input[type='checkbox']");
    if (theCheckboxes.filter(":checked").length > 3)

jquery animate .css

You can actually still use ".css" and apply css transitions to the div being affected. So continue using ".css" and add the below styles to your stylesheet for "#hfont1". Since ".css" allows for a lot more properties than ".animate", this is always my preferred method.

#hfont1 {
    -webkit-transition: width 0.4s;
    transition: width 0.4s;

Windows batch: call more than one command in a FOR loop?

Using & is fine for short commands, but that single line can get very long very quick. When that happens, switch to multi-line syntax.

FOR /r %%X IN (*.txt) DO (
    ECHO %%X
    DEL %%X

Placement of ( and ) matters. The round brackets after DO must be placed on the same line, otherwise the batch file will be incorrect.

See if /?|find /V "" for details.

Make an html number input always display 2 decimal places

You can use Telerik's numerictextbox for a lot of functionality

<input id="account_rate" data-role="numerictextbox" data-format="#.000" data-min="0.001" data-max="100" data-decimals="3" data-spinners="false" data-bind="value: account_rate_value" onchange="APP.models.rates.buttons_state(true);" />

the core code is free to download

Make a dictionary with duplicate keys in Python

Python dictionaries don't support duplicate keys. One way around is to store lists or sets inside the dictionary.

One easy way to achieve this is by using defaultdict:

from collections import defaultdict

data_dict = defaultdict(list)

All you have to do is replace

data_dict[regNumber] = details



and you'll get a dictionary of lists.

Javascript date.getYear() returns 111 in 2011?

In order to comply with boneheaded precedent, getYear() returns the number of years since 1900.

Instead, you should call getFullYear(), which returns the actual year.

How to fade changing background image

If your trying to fade the backgound image but leave the foreground text/images you could use css to separate the background image into a new div and position it over the div containing the text/images then fade the background div.

Best Practices for Custom Helpers in Laravel 5

Having sifted through a variety of answers on SO and Google, I still couldn't find an optimal approach. Most answers suggest we leave the application and rely on 3rd party tool Composer to do the job, but I'm not convinced coupling to a tool just to include a file is wise.

Andrew Brown's answer came the closest to how I think it should be approached, but (at least in 5.1), the service provider step is unnecessary. Heisian's answer highlights the use of PSR-4 which brings us one step closer. Here's my final implementation for helpers in views:

First, create a helper file anywhere in your apps directory, with a namespace:

namespace App\Helpers;

class BobFinder
    static function bob()
        return '<strong>Bob?! Is that you?!</strong>';

Next, alias your class in config\app.php, in the aliases array:

'aliases' => [
    // Other aliases
    'BobFinder' => App\Helpers\BobFinder::class

And that should be all you need to do. PSR-4 and the alias should expose the helper to your views, so in your view, if you type:

{!! BobFinder::bob() !!}

It should output:

<strong>Bob?! Is that you?!</strong>

Best way to track onchange as-you-type in input type="text"?

I had a similar requirement (twitter style text field). Used onkeyup and onchange. onchange actually takes care of mouse paste operations during lost focus from the field.

[Update] In HTML5 or later, use oninput to get real time character modification updates, as explained in other answers above.

How should a model be structured in MVC?

More oftenly most of the applications will have data,display and processing part and we just put all those in the letters M,V and C.

Model(M)-->Has the attributes that holds state of application and it dont know any thing about V and C.

View(V)-->Has displaying format for the application and and only knows about how-to-digest model on it and does not bother about C.

Controller(C)---->Has processing part of application and acts as wiring between M and V and it depends on both M,V unlike M and V.

Altogether there is separation of concern between each. In future any change or enhancements can be added very easily.

Grep for beginning and end of line?

You probably want egrep. Try:

egrep '^[d-]rwx.*[0-9]$' usrLog.txt

Shortcut key for commenting out lines of Python code in Spyder

While the other answers got it right when it comes to add comments, in my case only the following worked.

  • Multi-line comment

    select the lines to be commented + Ctrl + 4

  • Multi-line uncomment

    select the lines to be uncommented + Ctrl + 1

CentOS 64 bit bad ELF interpreter

Just wanted to add a comment in BRPocock, but I don't have the sufficient privilegies.

So my contribution was for everyone trying to install IBM Integration Toolkit from IBM's Integration Bus bundle.

When you try to run "Installation Manager" command from folder /Integration_Toolkit/IM_Linux (the file to run is "install") you get the error showed in this post.

Further instructions to fix this problem you'll find in this IBM's web page:

Hope this helps for anybody trying to install that.

Delete a single record from Entity Framework?

u can do it simply like this

   public ActionResult Delete(int? id)
        using (var db = new RegistrationEntities())
            Models.RegisterTable Obj = new Models.RegisterTable();
            Registration.DAL.RegisterDbTable personalDetail = db.RegisterDbTable.Find(id);
            if (personalDetail == null)
                return HttpNotFound();
                Obj.UserID = personalDetail.UserID;
                Obj.FirstName = personalDetail.FName;
                Obj.LastName = personalDetail.LName;
                Obj.City = personalDetail.City;

            return View(Obj);

    [HttpPost, ActionName("Delete")]

    public ActionResult DeleteConfirmed(int? id)
        using (var db = new RegistrationEntities())
            Registration.DAL.RegisterDbTable personalDetail = db.RegisterDbTable.Find(id);
            return RedirectToAction("where u want it to redirect");


 public class RegisterTable

    public int UserID
    { get; set; }

    public string FirstName
    { get; set; }

    public string LastName
    { get; set; }

    public string Password
    { get; set; }

    public string City
    { get; set; }


view from which u will call it

 <table class="table">


    @foreach (var item in Model)
            <td> @item.FirstName </td>
            <td> @item.LastName </td>
            <td> @item.City</td>
                <a href="@Url.Action("Edit", "Registeration", new { id = item.UserID })">Edit</a> |
                <a href="@Url.Action("Details", "Registeration", new { id = item.UserID })">Details</a> |
                <a href="@Url.Action("Delete", "Registeration", new { id = item.UserID })">Delete</a>




i hope this will be easy for u to understand

Uses of content-disposition in an HTTP response header

For users, the .NET framework provides a class to create a content disposition header: System.Net.Mime.ContentDisposition

Basic usage:

var cd = new System.Net.Mime.ContentDisposition();
cd.FileName = "myFile.txt";
cd.ModificationDate = DateTime.UtcNow;
cd.Size = 100;
Response.AppendHeader("content-disposition", cd.ToString());

Need a good hex editor for Linux

Bless is a high quality, full featured hex editor.

It is written in mono/Gtk# and its primary platform is GNU/Linux. However it should be able to run without problems on every platform that mono and Gtk# run.

Bless currently provides the following features:

  • Efficient editing of large data files and block devices.
  • Multilevel undo - redo operations.
  • Customizable data views.
  • Fast data rendering on screen.
  • Multiple tabs.
  • Fast find and replace operations.
  • A data conversion table.
  • Advanced copy/paste capabilities.
  • Highlighting of selection pattern matches in the file.
  • Plugin based architecture.
  • Export of data to text and html (others with plugins).
  • Bitwise operations on data.
  • A comprehensive user manual.

wxHexEditor is another Free Hex Editor, built because there is no good hex editor for Linux system, specially for big files.

  • It uses 64 bit file descriptors (supports files or devices up to 2^64 bytes , means some exabytes but tested only 1 PetaByte file (yet). ).
  • It does NOT copy whole file to your RAM. That make it FAST and can open files (which sizes are Multi Giga < Tera < Peta < Exabytes)
  • Could open your devices on Linux, Windows or MacOSX.
  • Memory Usage : Currently ~10 MegaBytes while opened multiple > ~8GB files.
  • Could operate thru XOR encryption.
  • Written with C++/wxWidgets GUI libs and can be used with other OSes such as Mac OS, Windows as native application.
  • You can copy/edit your Disks, HDD Sectors with it.( Usefull for rescue files/partitions by hand. )
  • You can delete/insert bytes to file, more than once, without creating temp file.

DHEX is a more than just another hex editor: It includes a diff mode, which can be used to easily and conveniently compare two binary files. Since it is based on ncurses and is themeable, it can run on any number of systems and scenarios. With its utilization of search logs, it is possible to track changes in different iterations of files easily. Wikipedia article

You can sort on Linux to find some more here:

How can I specify system properties in Tomcat configuration on startup?

cliff.meyers's original answer that suggested using <env-entry> will not help when using only System.getProperty()

According to the Tomcat 6.0 docs <env-entry> is for JNDI. So that means it won't have any effect on System.getProperty().

With the <env-entry> from cliff.meyers's example, the following code


will return null, not the value "abc123ftw".

According to the Tomcat 6 docs, to use <env-entry> you'd have to write code like this to use <env-entry>:

// Obtain our environment naming context
Context initCtx = new InitialContext();
Context envCtx = (Context) initCtx.lookup("java:comp/env");

// Look up our data source
String s = (String)envCtx.lookup("SMTP_PASSWORD");

Caveat: I have not actually tried the example above. But I have tried <env-entry> with System.getProperty(), and that definitely does not work.

Failed to read artifact descriptor for org.apache.maven.plugins:maven-source-plugin:jar:2.4

Two possible situations :


If you are generally doing updates I would ..

  1. Begin a transaction
  2. Do the update
  3. Check the rowcount
  4. If it is 0 do the insert
  5. Commit

If you are generally doing inserts I would

  1. Begin a transaction
  2. Try an insert
  3. Check for primary key violation error
  4. if we got an error do the update
  5. Commit

This way you avoid the select and you are transactionally sound on Sqlite.

C dynamically growing array

These posts apparently are in the wrong order! This is #3 in a series of 3 posts. Sorry.

I've "taken a few MORE liberties" with Lie Ryan's code. The linked list admittedly was time-consuming to access individual elements due to search overhead, i.e. walking down the list until you find the right element. I have now cured this by maintaining an address vector containing subscripts 0 through whatever paired with memory addresses. This works because the address vector is allocated all-at-once, thus contiguous in memory. Since the linked-list is no longer required, I've ripped out its associated code and structure.

This approach is not quite as efficient as a plain-and-simple static array would be, but at least you don't have to "walk the list" searching for the proper item. You can now access the elements by using a subscript. To enable this, I have had to add code to handle cases where elements are removed and the "actual" subscripts wouldn't be reflected in the pointer vector's subscripts. This may or may not be important to users. For me, it IS important, so I've made re-numbering of subscripts optional. If renumbering is not used, program flow goes to a dummy "missing" element which returns an error code, which users can choose to ignore or to act on as required.

From here, I'd advise users to code the "elements" portion to fit their needs and make sure that it runs correctly. If your added elements are arrays, carefully code subroutines to access them, seeing as how there's extra array structure that wasn't needed with static arrays. Enjoy!

#include <glib.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>

// Code from
// For pointer-to-pointer info see:
typedef struct STRUCT_SS_VECTOR
{   size_t size; // # of vector elements
    void** items; // makes up one vector element's component contents
    int subscript; // this element's subscript nmbr, 0 thru whatever
 //   struct STRUCT_SS_VECTOR* this_element; // linked list via this ptr
 //   struct STRUCT_SS_VECTOR* next_element; // and next ptr
} ss_vector;

ss_vector* vector; // ptr to vector of components
ss_vector* missing_element(int subscript) // intercepts missing elements
{   printf("missing element at subscript %i\n",subscript);
    return NULL;

typedef struct TRACKER_VECTOR
{   int subscript;
    ss_vector* vector_ptr;
} tracker_vector;  // up to 20 or so, max suggested

tracker_vector* tracker;
int max_tracker=0; // max allowable # of elements in "tracker_vector"
int tracker_count=0; // current # of elements in "tracker_vector"
int tracker_increment=5; // # of elements to add at each expansion

void bump_tracker_vector(int new_tracker_count)
{   //init or lengthen tracker vector
    if(max_tracker==0) // not yet initialized
    { tracker=calloc(tracker_increment, sizeof(tracker_vector));
printf("initialized %i-element tracker vector of size %lu at %lu\n",max_tracker,sizeof(tracker_vector),(size_t)tracker);
    else if (max_tracker<=tracker_count) // append to existing tracker vector by writing a new one, copying old one
    {   tracker_vector* temp_tracker=calloc(max_tracker+tracker_increment,sizeof(tracker_vector));  
        for(int i=0;(i<max_tracker);i++){   temp_tracker[i]=tracker[i];} // copy old tracker to new
printf("  re-initialized %i-element tracker vector of size %lu at %lu\n",max_tracker,sizeof(tracker_vector),(size_t)tracker);
    } // else if
    // fall through for most "bumps"
}  // bump_tracker_vector()

ss_vector* ss_init_vector(size_t item_size) // item_size is size of one array member
{   ss_vector* vector= malloc(sizeof(ss_vector)); 
    vector->size = 0; // initialize count of vector component elements
    vector->items = calloc(1, item_size); // allocate & zero out memory for one linked list element
    bump_tracker_vector(0); // init/store the tracker vector
    return vector; //->this_element;
} // ss_init_vector()

ss_vector* ss_vector_append( int i) // ptr to this element, element nmbr
{   ss_vector* local_vec_element=0;
    local_vec_element= calloc(1,sizeof(ss_vector)); // memory for one component
    local_vec_element->subscript=i; //vec_element->size; 
    local_vec_element->size=i; // increment # of vector components
    bump_tracker_vector(i);  // increment/store tracker vector
    tracker[i].vector_ptr=local_vec_element; //->this_element;
    return local_vec_element;
}  // ss_vector_append()

void bubble_sort(void)
{   //  bubble sort
    struct TRACKER_VECTOR local_tracker;
    int i=0;
    {   if(tracker[i].subscript>tracker[i+1].subscript)
        {   local_tracker.subscript=tracker[i].subscript; // swap tracker elements
            if(i>0) i--; // step back and go again
        {   if(i<tracker_count-1) i++;
    } // while()
} // void bubble_sort()

void move_toward_zero(int target_subscript) // toward zero
{   struct TRACKER_VECTOR local_tracker;
    // Target to be moved must range from 1 to max_tracker
    if((target_subscript<1)||(target_subscript>tracker_count)) return; // outside range
    // swap target_subscript ptr and target_subscript-1 ptr

void renumber_all_subscripts(gboolean arbitrary)
{   // assumes tracker_count has been fixed and tracker[tracker_count+1]has been zeroed out
    if(arbitrary)  // arbitrary renumber, ignoring "true" subscripts
    {   for(int i=0;i<tracker_count;i++) 
        {   tracker[i].subscript=i;}
    else // use "true" subscripts, holes and all
    {   for(int i=0;i<tracker_count;i++) 
        {   if ((size_t)tracker[i].vector_ptr!=0) // renumbering "true" subscript tracker & vector_element
            {   tracker[i].subscript=tracker[i].vector_ptr->subscript;}
            else // renumbering "true" subscript tracker & NULL vector_element
            {   tracker[i].subscript=-1;}
        } // for()
    } // if(arbitrary) ELSE
} // renumber_all_subscripts()

void collapse_tracker_higher_elements(int target_subscript)
{   // Fix tracker vector by collapsing higher subscripts toward 0.
    //  Assumes last tracker element entry is discarded.
    int j;
    {   tracker[j].subscript=tracker[j+1].subscript;
    // Discard last tracker element and adjust count
} // void collapse_tracker_higher_elements()

void ss_vector_free_one_element(int target_subscript, gboolean Keep_subscripts) 
{   // Free requested element contents.
    //      Adjust subscripts if desired; otherwise, mark NULL.
    // ----special case: vector[0]
    if(target_subscript==0) // knock out zeroth element no matter what
    {   free(tracker[0].vector_ptr);} 
    // ----if not zeroth, start looking at other elements
    else if(tracker_count<target_subscript-1)
    {   printf("vector element not found\n");return;}
    // Requested subscript okay. Freeit. 
    {   free(tracker[target_subscript].vector_ptr);} // free element ptr
    // done with removal.
    if(Keep_subscripts) // adjust subscripts if required.
    {   tracker[target_subscript].vector_ptr=missing_element(target_subscript);} // point to "0" vector
    else // NOT keeping subscripts intact, i.e. collapsing/renumbering all subscripts toward zero
    {   collapse_tracker_higher_elements(target_subscript);
        renumber_all_subscripts(TRUE); // gboolean arbitrary means as-is, FALSE means by "true" subscripts
    } // if (target_subscript==0) else
// show the new list
// for(int i=0;i<tracker_count;i++){printf("   remaining element[%i] at %lu\n",tracker[i].subscript,(size_t)tracker[i].vector_ptr);}
} // void ss_vector_free_one_element()

void ss_vector_free_all_elements(void) 
{   // Start at "tracker[0]". Walk the entire list, free each element's contents, 
    //      then free that element, then move to the next one.
    //      Then free the "tracker" vector.
    for(int i=tracker_count;i>=0;i--) 
    {   // Modify your code to free vector element "items" here
        if(tracker[i].subscript>=0) free(tracker[i].vector_ptr);
} // void ss_vector_free_all_elements()

// defining some sort of struct, can be anything really
typedef struct APPLE_STRUCT
{   int id; // one of the data in the component
    int other_id; // etc
    struct APPLE_STRUCT* next_element;
} apple; // description of component

apple* init_apple(int id) // make a single component
{   apple* a; // ptr to component
    a = malloc(sizeof(apple)); // memory for one component
    a->id = id; // populate with data
    // don't mess with aa->last_rec here
    return a; // return pointer to component

int return_id_value(int i,apple* aa) // given ptr to component, return single data item
{   printf("was inserted as apple[%i].id = %i     ",i,aa->id);

ss_vector* return_address_given_subscript(int i) 
{   return tracker[i].vector_ptr;} 

int Test(void)  // was "main" in the example
{   int i;
    ss_vector* local_vector;
    local_vector=ss_init_vector(sizeof(apple)); // element "0"
    for (i = 1; i < 10; i++) // inserting items "1" thru whatever
    {local_vector=ss_vector_append(i);}   // finished ss_vector_append()
    // list all tracker vector entries
    for(i=0;(i<tracker_count);i++) {printf("tracker element [%i] has address %lu\n",tracker[i].subscript, (size_t)tracker[i].vector_ptr);}
    // ---test search function
    printf("\n NEXT, test search for address given subscript\n");
printf("finished return_address_given_subscript(5) with vector at %lu\n",(size_t)local_vector);
printf("finished return_address_given_subscript(0) with vector at %lu\n",(size_t)local_vector);
printf("finished return_address_given_subscript(9) with vector at %lu\n",(size_t)local_vector);
    // ---test single-element removal
    printf("\nNEXT, test single element removal\n");
    ss_vector_free_one_element(5,TRUE); // keep subscripts; install dummy error element
printf("finished ss_vector_free_one_element(5)\n");
printf("finished ss_vector_free_one_element(3)\n");
    // ---test moving elements
printf("\n Test moving a few elements up\n");
    // show the new list
    printf("New list:\n");
    for(int i=0;i<tracker_count;i++){printf("   %i:element[%i] at %lu\n",i,tracker[i].subscript,(size_t)tracker[i].vector_ptr);}
    // ---plant some bogus subscripts for the next subscript test
printf("\n RENUMBER to use \"actual\" subscripts\n");   
    printf("Sorted list:\n");
    for(int i=0;i<tracker_count;i++)
    {   if ((size_t)tracker[i].vector_ptr!=0)
        {   printf("   %i:element[%i] or [%i]at %lu\n",i,tracker[i].subscript,tracker[i].vector_ptr->subscript,(size_t)tracker[i].vector_ptr);
        {   printf("   %i:element[%i] at 0\n",i,tracker[i].subscript);
printf("\nBubble sort to get TRUE order back\n");
    printf("Sorted list:\n");
    for(int i=0;i<tracker_count;i++)
    {   if ((size_t)tracker[i].vector_ptr!=0)
        {printf("   %i:element[%i] or [%i]at %lu\n",i,tracker[i].subscript,tracker[i].vector_ptr->subscript,(size_t)tracker[i].vector_ptr);}
        else {printf("   %i:element[%i] at 0\n",i,tracker[i].subscript);}
    // don't forget to free everything
    return 0;

int main(int argc, char *argv[])
{   char cmd[5],main_buffer[50]; // Intentionally big for "other" I/O purposes
    cmd[0]=32; // blank = ASCII 32
    //  while(cmd!="R"&&cmd!="W"  &&cmd!="E"        &&cmd!=" ") 
    {   memset(cmd, '\0', sizeof(cmd));
        memset(main_buffer, '\0', sizeof(main_buffer));
        // default back to the cmd loop
        cmd[0]=32; // blank = ASCII 32
        printf("REad, TEst, WRITe, EDIt, or EXIt? ");
        fscanf(stdin, "%s", main_buffer);
        for(int i=0;i<4;i++)cmd[i]=toupper(cmd[i]);
        printf("%s received\n ",cmd);
        // process top level commands
        if(cmd[0]==82) {printf("READ accepted\n");} //Read
        else if(cmd[0]==87) {printf("WRITe accepted\n");} // Write
        else if(cmd[0]==84) 
        {   printf("TESt accepted\n");// TESt
        else if(cmd[0]==69) // "E"
        {   if(cmd[1]==68) {printf("EDITing\n");} // eDit
            else if(cmd[1]==88) {printf("EXITing\n");exit(0);} // eXit
            else    printf("  unknown E command %c%c\n",cmd[0],cmd[1]);
        else    printf("  unknown command\n");
        cmd[0]=32; // blank = ASCII 32
    } // while()
    // default back to the cmd loop
}   // main()

How to set calculation mode to manual when opening an excel file?

The best way around this would be to create an Excel called 'launcher.xlsm' in the same folder as the file you wish to open. In the 'launcher' file put the following code in the 'Workbook' object, but set the constant TargetWBName to be the name of the file you wish to open.

Private Const TargetWBName As String = "myworkbook.xlsx"

'// First, a function to tell us if the workbook is already open...
Function WorkbookOpen(WorkBookName As String) As Boolean
' returns TRUE if the workbook is open
    WorkbookOpen = False
    On Error GoTo WorkBookNotOpen
    If Len(Application.Workbooks(WorkBookName).Name) > 0 Then
        WorkbookOpen = True
        Exit Function
    End If
End Function

Private Sub Workbook_Open()
    'Check if our target workbook is open
    If WorkbookOpen(TargetWBName) = False Then
        'set calculation to manual
        Application.Calculation = xlCalculationManual
        Workbooks.Open ThisWorkbook.Path & "\" & TargetWBName
        Me.Close False
    End If
End Sub

Set the constant 'TargetWBName' to be the name of the workbook that you wish to open. This code will simply switch calculation to manual, then open the file. The launcher file will then automatically close itself. *NOTE: If you do not wish to be prompted to 'Enable Content' every time you open this file (depending on your security settings) you should temporarily remove the 'me.close' to prevent it from closing itself, save the file and set it to be trusted, and then re-enable the 'me.close' call before saving again. Alternatively, you could just set the False to True after Me.Close

Python - Passing a function into another function

Just pass it in, like this:

Game(list_a, list_b, Rule1)

and then your Game function could look something like this (still pseudocode):

def Game(listA, listB, rules=None):
    if rules:
        # do something useful
        # ...
        result = rules(variable) # this is how you can call your rule
        # do something useful without rules

Preloading @font-face fonts?

This should solve your problem.

To answer your initial question: yes you can. Only Gecko and WebKit browsers support it currently though.
You just need to add link tags in your head:

<link rel="prefetch" href="pathto/font">
<link rel="prerender" href="pathto/page">

OnClickListener in Android Studio

Button button= (Button) findViewById(;
button.setOnClickListener(new View.OnClickListener() {
    public void onClick(View v) {
        startActivity(new Intent(MainActivity.this,StandingsActivity.class));

This code is not in any method. If you want to use it, it must be within a method like OnCreate()

protected void onCreate(Bundle savedInstanceState) {

    Button button= (Button) findViewById(;
    button.setOnClickListener(new View.OnClickListener() {
        public void onClick(View v) {
            startActivity(new Intent(MainActivity.this,StandingsActivity.class));

How do I pass a unique_ptr argument to a constructor or a function?

Base(Base::UPtr n):next(std::move(n)) {}

should be much better as

Base(Base::UPtr&& n):next(std::forward<Base::UPtr>(n)) {}


void setNext(Base::UPtr n)

should be

void setNext(Base::UPtr&& n)

with same body.

And ... what is evt in handle() ??

Sum values from an array of key-value pairs in JavaScript

Creating a sum method would work nicely, e.g. you could add the sum function to Array

Array.prototype.sum = function(selector) {
    if (typeof selector !== 'function') {
        selector = function(item) {
            return item;
    var sum = 0;
    for (var i = 0; i < this.length; i++) {
        sum += parseFloat(selector(this[i]));
    return sum;

then you could do

> [1,2,3].sum()

and in your case

> myData.sum(function(item) { return item[1]; });

Edit: Extending the builtins can be frowned upon because if everyone did it we would get things unexpectedly overriding each other (namespace collisions). you could add the sum function to some module and accept an array as an argument if you like. that could mean changing the signature to myModule.sum = function(arr, selector) { then this would become arr

How to escape regular expression special characters using javascript?

Use the backslash to escape a character. For example:


This will match \d instead of a numeric character

"Could not find a valid gem in any repository" (rubygame and others)

Can you post your versions?

ruby -v
#=> ruby 1.9.3p125 (2012-02-16 revision 34643) [x86_64-linux]

gem -v
#=> 1.8.19

If your gem command is not current, you can update it like this:

gem update --system

To see if you can connect to using Ruby:

require 'net/http'
require 'uri'
puts Net::HTTP.get URI.parse('')

If yes, that's good.

If no, then somehow Ruby is blocked from opening a net connection. Try these and see if any of them work:


curl --local-port 1080

curl --local-port 8080

env | grep -i proxy

If you're using a company machine, or within a company firewall, or running your own firewall, you may need to use a proxy.

For info on Ruby and proxies see

How to update column value in laravel

I tried to update a field with

$table->update(['field' => 'val']);

But it wasn't working, i had to modify my table Model to authorize this field to be edited : add 'field' in the array "protected $fillable"

Hope it will help someone :)

How to know if docker is already logged in to a docker registry server

You can do the following command to see the username you are logged in with and the registry used:

docker system info | grep -E 'Username|Registry'

How to express a NOT IN query with ActiveRecord/Rails?

Piggybacking off of jonnii:

Topic.find(:all, :conditions => ['forum_id not in (?)', @forums.pluck(:id)])

using pluck rather than mapping over the elements

found via railsconf 2012 10 things you did not know rails could do

How to delete specific characters from a string in Ruby?

Do as below using String#tr :

 "((String1))".tr('()', '')
 # => "String1"

HTML table with fixed headers and a fixed column?

Here is a good jQuery plugin, working in all browsers!

You have a fixed header table without fixing its width.

Check it:

Disclaimer: I am the author of the plugin.

Auto reloading python Flask app upon code changes

I got a different idea:


pip install python-dotenv

Install the python-dotenv module, which will read local preference for your project environment.


Add .flaskenv file in your project directory. Add following code:


It's done!

With this config for your Flask project, when you run flask run and you will see this output in your terminal:

enter image description here

And when you edit your file, just save the change. You will see auto-reload is there for you:

enter image description here

With more explanation:

Of course you can manually hit export FLASK_ENV=development every time you need. But using different configuration file to handle the actual working environment seems like a better solution, so I strongly recommend this method I use.

How can I print literal curly-brace characters in a string and also use .format on it?

Use escape sequences to escape the curly braces in the f-string. Ex:print(f'{a={1}}')

How does String substring work in Swift

Same frustration, this should not be that hard...

I compiled this example of getting positions for substring(s) from larger text:

// Play with finding substrings returning an array of the non-unique words and positions in text

import UIKit

let Bigstring = "Why is it so hard to find substrings in Swift3"
let searchStrs : Array<String>? = ["Why", "substrings", "Swift3"]

FindSubString(inputStr: Bigstring, subStrings: searchStrs)

func FindSubString(inputStr : String, subStrings: Array<String>?) ->    Array<(String, Int, Int)> {
    var resultArray : Array<(String, Int, Int)> = []
    for i: Int in 0...(subStrings?.count)!-1 {
        if inputStr.contains((subStrings?[i])!) {
            let range: Range<String.Index> = inputStr.range(of: subStrings![i])!
            let lPos = inputStr.distance(from: inputStr.startIndex, to: range.lowerBound)
            let uPos = inputStr.distance(from: inputStr.startIndex, to: range.upperBound)
            let element = ((subStrings?[i])! as String, lPos, uPos)
    for words in resultArray {
    return resultArray

returns ("Why", 0, 3) ("substrings", 26, 36) ("Swift3", 40, 46)

adding 30 minutes to datetime php/mysql

If you are using MySQL you can do it like this:

SELECT '2008-12-31 23:59:59' + INTERVAL 30 MINUTE;

For a pure PHP solution use strtotime

strtotime('+ 30 minute',$yourdate);

Calling Python in Java?

It depends on what do you mean by python functions? if they were written in cpython you can not directly call them you will have to use JNI, but if they were written in Jython you can easily call them from java, as jython ultimately generates java byte code.

Now when I say written in cpython or jython it doesn't make much sense because python is python and most code will run on both implementations unless you are using specific libraries which relies on cpython or java.

see here how to use Python interpreter in Java.

How can I get the Google cache age of any URL or web page?

This one good also to view cachepage

  1. Cache page view via google: Your url

  2. Cache page view via*/Your url

Get the difference between dates in terms of weeks, months, quarters, and years

try this for a months solution

StartDate <- strptime("14 January 2013", "%d %B %Y") 
EventDates <- strptime(c("26 March 2014"), "%d %B %Y") 
difftime(EventDates, StartDate) 

Calling one Activity from another in Android

Add the following to your on button click event:

Intent intent = new Intent(First.this, Second.class);

What is the difference between "SMS Push" and "WAP Push"?

An SMS Push is a message to tell the terminal to initiate the session. This happens because you can't initiate an IP session simply because you don't know the IP Adress of the mobile terminal. Mostly used to send a few lines of data to end recipient, to the effect of sending information, or reminding of events.

WAP Push is an SMS within the header of which is included a link to a WAP address. On receiving a WAP Push, the compatible mobile handset automatically gives the user the option to access the WAP content on his handset. The WAP Push directs the end-user to a WAP address where content is stored ready for viewing or downloading onto the handset. This wap address may be a page or a WAP site.

The user may “take action” by using a developer-defined soft-key to immediately activate an application to accomplish a specific task, such as downloading a picture, making a purchase, or responding to a marketing offer.

How to import js-modules into TypeScript file?

I'm currently taking some legacy codebases and introducing minimal TypeScript changes to see if it helps our team. Depending on how strict you want to be with TypeScript, this may or may not be an option for you.

The most helpful way for us to get started was to extend our tsconfig.json file with this property:

// tsconfig.json excerpt:

  "compilerOptions": {
    "allowJs": true,

This change lets our JS files that have JSDoc type hints get compiled. Also our IDEs (JetBrains IDEs and VS Code) can provide code-completion and Intellisense.


How can I get the DateTime for the start of the week?

A little more verbose and culture-aware:

System.Globalization.CultureInfo ci = 
DayOfWeek fdow = ci.DateTimeFormat.FirstDayOfWeek;
DayOfWeek today = DateTime.Now.DayOfWeek;
DateTime sow = DateTime.Now.AddDays(-(today - fdow)).Date;

How to pass List<String> in post method using Spring MVC?

You can pass input as ["apple","orange"]if you want to leave the method as it is.

It worked for me with a similar method signature.

Common elements in two lists

You can use set intersection operations with your ArrayList objects.

Something like this:

List<Integer> l1 = new ArrayList<Integer>();


List<Integer> l2= new ArrayList<Integer>();

System.out.println("l1 == "+l1);
System.out.println("l2 == "+l2);

List<Integer> l3 = new ArrayList<Integer>(l2);

    System.out.println("l3 == "+l3);

Now, l3 should have only common elements between l1 and l2.

l1 == [1, 2, 3]
l2 == [4, 2, 3]
l3 == [2, 3]

Nested ifelse statement

Using the SQL CASE statement with the dplyr and sqldf packages:


df <-structure(list(idnat = structure(c(2L, 2L, 2L, 1L), .Label = c("foreign", 
"french"), class = "factor"), idbp = structure(c(3L, 1L, 4L, 
2L), .Label = c("colony", "foreign", "mainland", "overseas"), class = "factor")), .Names = c("idnat", 
"idbp"), class = "data.frame", row.names = c(NA, -4L))


sqldf("SELECT idnat, idbp,
          WHEN idbp IN ('colony', 'overseas') THEN 'overseas' 
          ELSE idbp 
        END AS idnat2
       FROM df")


df %>% 
mutate(idnat2 = case_when(.$idbp == 'mainland' ~ "mainland", 
                          .$idbp %in% c("colony", "overseas") ~ "overseas", 
                         TRUE ~ "foreign"))


    idnat     idbp   idnat2
1  french mainland mainland
2  french   colony overseas
3  french overseas overseas
4 foreign  foreign  foreign

Find methods calls in Eclipse project

Go to the method in, and select Open Call Hierarchy from the context menu.

Sibling package imports

in your main file add this:

import sys
import os 

mainScriptDepth = the depth of the main file from the root of the project.

Here in your case mainScriptDepth = "../../".

How to split a string literal across multiple lines in C / Objective-C?

There are two ways to split strings over multiple lines:

Using \

All lines in C can be split into multiple lines using \.

Plain C:

char *my_string = "Line 1 \
                   Line 2";


NSString *my_string = @"Line1 \

Better approach

There's a better approach that works just for strings.

Plain C:

char *my_string = "Line 1 "
                  "Line 2";


NSString *my_string = @"Line1 "
                       "Line2";    // the second @ is optional

The second approach is better, because there isn't a lot of whitespace included. For a SQL query however, both are possible.

NOTE: With a #define, you have to add an extra '\' to concatenate the two strings:

Plain C:

#define kMyString "Line 1"\
                  "Line 2"

Android Studio with Google Play Services

EDITED: This guy really brought it home and has a good little tutorial

one side note: I had played around so much that I needed to do a gradlew clean to get it to run succesfully

If you have imported your project or are working from the Sample Maps application located in \extras\google\google_play_services\samples\maps check out this tutorial.

If you are creating a new project from scratch then note Xav's comments on that same post. He describes that Android Studio uses a different compiler and that you have to modify the build.gradle file manually. I did this with success. I copied

  • google-play-services.jar

into my lib directory and added the following to my build.gradle file

dependencies {
    compile files('libs/android-support-v4.jar')
    compile files('libs/google-play-services.jar')

Also, if this is a new project check out this post, too.

ImportError: No module named six

You probably don't have the six Python module installed. You can find it on pypi.

To install it:

$ easy_install six

(if you have pip installed, use pip install six instead)

NPM: npm-cli.js not found when running npm

Updating NPM to the latest version worked for me:

npm install npm@latest -g

Adding values to specific DataTable cells

Try this:

dt.Rows[RowNumber]["ColumnName"] = "Your value"

For example: if you want to add value 5 (number 5) to 1st row and column name "index" you would do this

dt.Rows[0]["index"] = 5;

I believe DataTable row starts with 0

Is there an equivalent to the SUBSTRING function in MS Access SQL?

I couldn't find an off-the-shelf module that added this function, so I wrote one:

In Access, go to the Database Tools ribbon, in the Macro area click into Visual Basic. In the top left Project area, right click the name of your file and select Insert -> Module. In the module paste this:

Public Function Substring_Index(strWord As String, strDelim As String, intCount As Integer) As String

Substring_Index = delims

start = 0
test = ""

For i = 1 To intCount
    oldstart = start + 1
    start = InStr(oldstart, strWord, strDelim)
    Substring_Index = Mid(strWord, oldstart, start - oldstart)
Next i

End Function

Save the module as module1 (the default). You can now use statements like:

SELECT Substring_Index([fieldname],",",2) FROM table

Select an Option from the Right-Click Menu in Selenium Webdriver - Java

Right click can be achieved using Java script executor as well(in cases where action class is not supported):

JavascriptExecutor js = (JavascriptExecutor) driver;

String javaScript = "var evt = document.createEvent('MouseEvents');"
                + "var RIGHT_CLICK_BUTTON_CODE = 2;"
                + "evt.initMouseEvent('contextmenu', true, true, window, 1, 0, 0, 0, 0, false, false, false, false, RIGHT_CLICK_BUTTON_CODE, null);"
                + "arguments[0].dispatchEvent(evt)";

js.executeScript(javaScript, element);

Apply style to cells of first row

Use tr:first-child to take the first tr:

.category_table tr:first-child td {
    vertical-align: top;

If you have nested tables, and you don't want to apply styles to the inner rows, add some child selectors so only the top-level tds in the first top-level tr get the styles:

.category_table > tbody > tr:first-child > td {
    vertical-align: top;

move div with CSS transition

This may be the good solution for you: change the code like this very little change

    position: relative; 
.box:hover .hidden{
    opacity: 1;
.box .hidden{
    background: yellow;
    height: 334px; 
    position: absolute;
    top: 0;
    left: 0;
    width: 0;
    opacity: 0;
    transition: all 1s ease;

See demo here

In Python script, how do I set PYTHONPATH?

You don't set PYTHONPATH, you add entries to sys.path. It's a list of directories that should be searched for Python packages, so you can just append your directories to that list.


In fact, sys.path is initialized by splitting the value of PYTHONPATH on the path separator character (: on Linux-like systems, ; on Windows).

You can also add directories using site.addsitedir, and that method will also take into account .pth files existing within the directories you pass. (That would not be the case with directories you specify in PYTHONPATH.)

jquery (or pure js) simulate enter key pressed for testing

For those who want to do this in pure javascript, look at:

Using standard KeyboardEvent

As Joe comment it, KeyboardEvent is now the standard.

Same example to fire an enter (keyCode 13):

const ke = new KeyboardEvent('keydown', {
    bubbles: true, cancelable: true, keyCode: 13

You can use this page help you to find the right keyboard event.

Outdated answer:

You can do something like (here for Firefox)

var ev = document.createEvent('KeyboardEvent');
// Send key '13' (= enter)
    'keydown', true, true, window, false, false, false, false, 13, 0);

multiple plot in one figure in Python

Since I don't have a high enough reputation to comment I'll answer liang question on Feb 20 at 10:01 as an answer to the original question.

In order for the for the line labels to show you need to add plt.legend to your code. to build on the previous example above that also includes title, ylabel and xlabel:

import matplotlib.pyplot as plt

plt.plot(<X AXIS VALUES HERE>, <Y AXIS VALUES HERE>, 'line type', label='label here')
plt.plot(<X AXIS VALUES HERE>, <Y AXIS VALUES HERE>, 'line type', label='label here')

What does \0 stand for?

\0 is zero character. In C it is mostly used to indicate the termination of a character string. Of course it is a regular character and may be used as such but this is rarely the case.

The simpler versions of the built-in string manipulation functions in C require that your string is null-terminated(or ends with \0).

Matplotlib/pyplot: How to enforce axis range?

I tried all of those above answers, and I then summarized a pipeline of how to draw the fixed-axes image. It applied both to show function and savefig function.

  1. before you plot:

    fig = pylab.figure()
    ax = fig.gca()

This is to request an ax which is subplot(1,1,1).

  1. During the plot:

    ax.plot('You plot argument') # Put inside your argument, like ax.plot(x,y,label='test')
    ax.axis('The list of range') # Put in side your range [xmin,xmax,ymin,ymax], like ax.axis([-5,5,-5,200])
  2. After the plot:

    1. To show the image :
    2. To save the figure :

      fig.savefig('the name of your figure')

I find out that put axis at the front of the code won't work even though I have set autoscale_on to False.

I used this code to create a series of animation. And below is the example of combing multiple fixed axes images into an animation. img

Responsive iframe using Bootstrap

The best solution that worked great for me.

You have to: Copy this code to your main CSS file,

.responsive-video {
    position: relative;
    padding-bottom: 56.25%;
    padding-top: 60px; overflow: hidden;

.responsive-video iframe,
.responsive-video object,
.responsive-video embed {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;

and then put your embeded video to

<div class="responsive-video">
    <iframe ></iframe>

That’s it! Now you can use responsive videos on your site.

React ignores 'for' attribute of the label element

For React you must use it's per-define keywords to define html attributes.

class -> className

is used and

for -> htmlFor

is used, as react is case sensitive make sure you must follow small and capital as required.

Rename a column in MySQL

Rename column name in mysql

alter table categories change  type  category_type varchar(255);

Check if all values in list are greater than a certain number

You can use all():

my_list1 = [30,34,56]
my_list2 = [29,500,43]
if all(i >= 30 for i in my_list1):
    print 'yes'
if all(i >= 30 for i in my_list2):
    print 'no'

Note that this includes all numbers equal to 30 or higher, not strictly above 30.

How to connect to a secure website using SSL in Java with a pkcs12 file?

This is an example to use ONLY p12 file it's not optimazed but it work. The pkcs12 file where generated by OpenSSL by me. Example how to load p12 file and build Trust zone from it... It outputs certificates from p12 file and add good certs to TrustStore

KeyStore ks=KeyStore.getInstance("pkcs12");
ks.load(new FileInputStream("client_t_c1.p12"),"c1".toCharArray());

KeyStore jks=KeyStore.getInstance("JKS");

for (Enumeration<String>t=ks.aliases();t.hasMoreElements();)
    String alias = t.nextElement();
    System.out.println("@:" + alias);
    if (ks.isKeyEntry(alias)){
        Certificate[] a = ks.getCertificateChain(alias);
        for (int i=0;i<a.length;i++)
            X509Certificate x509 = (X509Certificate)a[i];
            if (i>0)
                jks.setCertificateEntry(x509.getSubjectDN().toString(), x509);

System.out.println("init Stores...");

KeyManagerFactory kmf=KeyManagerFactory.getInstance("SunX509");
kmf.init(ks, "c1".toCharArray());

TrustManagerFactory tmf=TrustManagerFactory.getInstance("SunX509");

SSLContext ctx = SSLContext.getInstance("TLS");
ctx.init(kmf.getKeyManagers(), tmf.getTrustManagers(), null);

How can I get phone serial number (IMEI)

public String getIMEI(Context context){

    TelephonyManager mngr = (TelephonyManager) context.getSystemService(context.TELEPHONY_SERVICE); 
    String imei = mngr.getDeviceId();
    return imei;


Tomcat Server Error - Port 8080 already in use

Since it is easy to tackle with Command Prompt. Open the CMD and type following.

netstat -aon | find "8080"

If a process uses above port, it should return something output like this.

TCP    xxx.xx.xx.xx:8080      ESTABLISHED     2222

The last column value (2222) is referred to the Process ID (PID).

Just KILL it as follows.

taskkill /F /PID 2222

Now you can start your server.

How to make external HTTP requests with Node.js

I would combine node-http-proxy and express.

node-http-proxy will support a proxy inside your node.js web server via RoutingProxy (see the example called Proxy requests within another http server).

Inside your custom server logic you can do authentication using express. See the auth sample here for an example.

Combining those two examples should give you what you want.

show distinct column values in pyspark dataframe: python

You can use df.dropDuplicates(['col1','col2']) to get only distinct rows based on colX in the array.

Windows recursive grep command-line

If you have Perl installed, you could use ack, available at

Remove icon/logo from action bar on android

If you do not want the icon in particular activity.

   new ColorDrawable(getResources().getColor(android.R.color.transparent)));    

ExpressionChangedAfterItHasBeenCheckedError: Expression has changed after it was checked. Previous value: 'undefined'

Try this, to call your code in ngOnInit()

someMethod() // emitted method call from output
    // Your code 

  someMethod(); // call here your error will be gone

replacing text in a file with Python

Faster way of writing it would be...

in = open('path/to/input/file').read()
out = open('path/to/input/file', 'w')
replacements = {'zero':'0', 'temp':'bob', 'garbage':'nothing'}
for i in replacements.keys():
    in = in.replace(i, replacements[i])

This eliminated a lot of the iterations that the other answers suggest, and will speed up the process for longer files.

Mongoose delete array element in document and save

This is working for me and really very helpful.

SubCategory.update({ _id: { $in: (obj) {
            return mongoose.Types.ObjectId(obj);
    } },
        $pull: {
            coupon: couponId,
    }, { multi: true }, function (err, numberAffected) {
        if(err) {
            return callback({

I have a model which name is SubCategory and I want to remove Coupon from this category Array. I have an array of categories so I have used arrOfSubCategory. So I fetch each array of object from this array with map function with the help of $in operator.

Make a div into a link

Actually you need to include the JavaScript code at the moment, check this tutorial to do so.

but there is a tricky way to achieve this using a CSS code you must nest an anchor tag inside your div tag and you must apply this property to it,


when you've done that,it will make the whole width area clickable (but within the height of the anchor tag),if you want to cover the whole div area you must set the height of the anchor tag exactly to the height of the div tag,for example:


this is gonna make the whole area clickable,then you can apply text-indent:-9999px to anchor tag to achieve the goal.

this is really tricky and simple and it's just created using CSS code.

here is an example:

How can I set an SQL Server connection string?

We can simply connect to the database like this:


For example:

string connectionString = @"uid=spacecraftU1;pwd=Appolo11;
SqlConnection con = new SqlConnection(connectionString);

Iterate over object in Angular

I had a similar issue, built something for objects and Maps.

import { Pipe } from 'angular2/core.js';_x000D_
 * Map to Iteratble Pipe_x000D_
 * _x000D_
 * It accepts Objects and [Maps](
 * _x000D_
 * Example:_x000D_
 * _x000D_
 *  <div *ngFor="#keyValuePair of someObject | mapToIterable">_x000D_
 *    key {{keyValuePair.key}} and value {{keyValuePair.value}}_x000D_
 *  </div>_x000D_
 * _x000D_
@Pipe({ name: 'mapToIterable' })_x000D_
export class MapToIterable {_x000D_
  transform(value) {_x000D_
    let result = [];_x000D_
    if(value.entries) {_x000D_
      for (var [key, value] of value.entries()) {_x000D_
        result.push({ key, value });_x000D_
    } else {_x000D_
      for(let key in value) {_x000D_
        result.push({ key, value: value[key] });_x000D_
    return result;_x000D_

Typescript: No index signature with a parameter of type 'string' was found on type '{ "A": string; }

You can fix the errors by validating your input, which is something you should do regardless of course.

The following typechecks correctly, via type guarding validations

const DNATranscriber = {
    G: 'C',
    C: 'G',
    T: 'A',
    A: 'U'

export default class Transcriptor {
    toRna(dna: string) {
        const codons = [...dna];
        if (!isValidSequence(codons)) {
            throw Error('invalid sequence');
        const transcribedRNA = => DNATranscriber[codon]);
        return transcribedRNA;

function isValidSequence(values: string[]): values is Array<keyof typeof DNATranscriber> {
    return values.every(isValidCodon);
function isValidCodon(value: string): value is keyof typeof DNATranscriber {
    return value in DNATranscriber;

It is worth mentioning that you seem to be under the misapprehention that converting JavaScript to TypeScript involves using classes.

In the following, more idiomatic version, we leverage TypeScript to improve clarity and gain stronger typing of base pair mappings without changing the implementation. We use a function, just like the original, because it makes sense. This is important! Converting JavaScript to TypeScript has nothing to do with classes, it has to do with static types.

const DNATranscriber = {
    G = 'C',
    C = 'G',
    T = 'A',
    A = 'U'

export default function toRna(dna: string) {
    const codons = [...dna];
    if (!isValidSequence(codons)) {
        throw Error('invalid sequence');
    const transcribedRNA = => DNATranscriber[codon]);
    return transcribedRNA;

function isValidSequence(values: string[]): values is Array<keyof typeof DNATranscriber> {
    return values.every(isValidCodon);
function isValidCodon(value: string): value is keyof typeof DNATranscriber {
    return value in DNATranscriber;


Since TypeScript 3.7, we can write this more expressively, formalizing the correspondence between input validation and its type implication using assertion signatures.

const DNATranscriber = {
    G = 'C',
    C = 'G',
    T = 'A',
    A = 'U'
} as const;

type DNACodon = keyof typeof DNATranscriber;
type RNACodon = typeof DNATranscriber[DNACodon];

export default function toRna(dna: string): RNACodon[] {
    const codons = [...dna];
    const transcribedRNA = => DNATranscriber[codon]);
    return transcribedRNA;

function validateSequence(values: string[]): asserts values is DNACodon[] {
    if (!values.every(isValidCodon)) {
        throw Error('invalid sequence');    
function isValidCodon(value: string): value is DNACodon {
    return value in DNATranscriber;

You can read more about assertion signatures in the TypeScript 3.7 release notes.

How to set up default schema name in JPA configuration?

For those who uses last versions of spring boot will help this:

.properties:<name of your schema>


                default_schema: <name of your schema>

Why does flexbox stretch my image rather than retaining aspect ratio?

I faced the same issue with a Foundation menu. align-self: center; didn't work for me.

My solution was to wrap the image with a <div style="display: inline-table;">...</div>

Setting HTTP headers

All of the above answers are wrong because they fail to handle the OPTIONS preflight request, the solution is to override the mux router's interface. See AngularJS $http get request failed with custom header (alllowed in CORS)

func main() {
    r := mux.NewRouter()
    r.HandleFunc("/save", saveHandler)
    http.Handle("/", &MyServer{r})
    http.ListenAndServe(":8080", nil);


type MyServer struct {
    r *mux.Router

func (s *MyServer) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
    if origin := req.Header.Get("Origin"); origin != "" {
        rw.Header().Set("Access-Control-Allow-Origin", origin)
        rw.Header().Set("Access-Control-Allow-Methods", "POST, GET, OPTIONS, PUT, DELETE")
            "Accept, Content-Type, Content-Length, Accept-Encoding, X-CSRF-Token, Authorization")
    // Stop here if its Preflighted OPTIONS request
    if req.Method == "OPTIONS" {
    // Lets Gorilla work
    s.r.ServeHTTP(rw, req)

How to install JRE 1.7 on Mac OS X and use it with Eclipse?

The download from which installs in /Library/Internet Plug-Ins is only the JRE, for development you probably want to download the JDK from and install that instead. This will install the JDK at /Library/Java/JavaVirtualMachines/jdk1.7.0_<something>.jdk/Contents/Home which you can then add to Eclipse via Preferences -> Java -> Installed JREs.

Already defined in .obj - no double inclusions

I do recomend doing it in 2 filles (.h .cpp) But if u lazy just add inline before the function So it will look something like this

inline void functionX() 
{ }

more about inline functions:

The inline functions are a C++ enhancement feature to increase the execution time of a program. Functions can be instructed to compiler to make them inline so that compiler can replace those function definition wherever those are being called. Compiler replaces the definition of inline functions at compile time instead of referring function definition at runtime. NOTE- This is just a suggestion to compiler to make the function inline, if function is big (in term of executable instruction etc) then, compiler can ignore the “inline” request and treat the function as normal function.

more info here

Custom CSS Scrollbar for Firefox

I thought I would share my findings in case someone is considering a JQuery plugin to do the job.

I gave JQuery Custom Scrollbar a go. It's pretty fancy and does some smooth scrolling (with scrolling inertia) and has loads of parameters you can tweak, but it ended up being a bit too CPU intensive for me (and it adds a fair amount to the DOM).

Now I'm giving Perfect Scrollbar a go. It's simple and lightweight (6KB) and it's doing a decent job so far. It's not CPU intensive at all (as far as I can tell) and adds very little to your DOM. It's only got a couple of parameters to tweak (wheelSpeed and wheelPropagation), but it's all I need and it handles updates to the scrolling content nicely (such as loading images).

P.S. I did have a quick look at JScrollPane, but @simone is right, it's a bit dated now and a PITA.

Detect when an HTML5 video finishes

Here is a simple approach which triggers when the video ends.


    <video id="myVideo" controls="controls">
        <source src="video.mp4" type="video/mp4">
        etc ...

<script type='text/javascript'>

    document.getElementById('myVideo').addEventListener('ended', function(e) {

        alert('The End');



In the 'EventListener' line substitute the word 'ended' with 'pause' or 'play' to capture those events as well.

if block inside echo statement?

In sake of readability it should be something like

  $countries = $myaddress->get_countries();
  foreach($countries as $value) {
    $selected ='';
    if($value=='United States') $selected ='selected="selected"'; 
    echo '<option value="'.$value.'"'.$selected.'>'.$value.'</option>';

desire to stuff EVERYTHING in a single line is a decease, man. Write distinctly.

But there is another way, a better one. There is no need to use echo at all. Learn to use templates. Prepare your data first, and display it only then ready.

Business logic part:

$countries = $myaddress->get_countries();
$selected_country = 1;    

Template part:

<? foreach($countries as $row): ?>
<option value="<?=$row['id']?>"<? if ($row['id']==$current_country):> "selected"><? endif ?>
<? endforeach ?>

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;

Does Enter key trigger a click event?

For angular 6 there is a new way of doing it. On your input tag add


Where keyUpFunction($event) is your function.

Test if numpy array contains only zeros

The other answers posted here will work, but the clearest and most efficient function to use is numpy.any():

>>> all_zeros = not np.any(a)


>>> all_zeros = not a.any()
  • This is preferred over numpy.all(a==0) because it uses less RAM. (It does not require the temporary array created by the a==0 term.)
  • Also, it is faster than numpy.count_nonzero(a) because it can return immediately when the first nonzero element has been found.
    • Edit: As @Rachel pointed out in the comments, np.any() no longer uses "short-circuit" logic, so you won't see a speed benefit for small arrays.

How do I pass an object to HttpClient.PostAsync and serialize as a JSON body?

You need to pass your data in the request body as a raw string rather than FormUrlEncodedContent. One way to do so is to serialize it into a JSON string:

var json = JsonConvert.SerializeObject(data); // or JsonSerializer.Serialize if using System.Text.Json

Now all you need to do is pass the string to the post method.

var stringContent = new StringContent(json, UnicodeEncoding.UTF8, "application/json"); // use MediaTypeNames.Application.Json in Core 3.0+ and Standard 2.1+

var client = new HttpClient();
var response = await client.PostAsync(uri, stringContent);

Using DISTINCT along with GROUP BY in SQL Server

Use DISTINCT to remove duplicate GROUPING SETS from the GROUP BY clause

In a completely silly example using GROUPING SETS() in general (or the special grouping sets ROLLUP() or CUBE() in particular), you could use DISTINCT in order to remove the duplicate values produced by the grouping sets again:

FROM (VALUES('a'), ('a'), ('b'), ('b')) t(actors)
GROUP BY CUBE(actors, actors)





But why, apart from making an academic point, would you do that?

Use DISTINCT to find unique aggregate function values

In a less far-fetched example, you might be interested in the DISTINCT aggregated values, such as, how many different duplicate numbers of actors are there?

FROM (VALUES('a'), ('a'), ('b'), ('b')) t(actors)
GROUP BY actors



Use DISTINCT to remove duplicates with more than one GROUP BY column

Another case, of course, is this one:

FROM (VALUES('a', 1), ('a', 1), ('b', 1), ('b', 2)) t(actors, id)
GROUP BY actors, id


actors  count
a       2
b       1


actors  count
a       2
b       1
b       1

For more details, I've written some blog posts, e.g. about GROUPING SETS and how they influence the GROUP BY operation, or about the logical order of SQL operations (as opposed to the lexical order of operations).

Bootstrap 3 Horizontal Divider (not in a dropdown)

As I found the default Bootstrap <hr/> size unsightly, here's some simple HTML and CSS to balance out the element visually:


<hr class="half-rule"/>


.half-rule { 
    margin-left: 0;
    text-align: left;
    width: 50%;

How can I monitor the thread count of a process on linux?

JStack is quite inexpensive - one option would be to pipe the output through grep to find active threads and then pipe through wc -l.

More graphically is JConsole, which displays the thread count for a given process.

Replace spaces with dashes and make all letters lower-case

Above answer can be considered to be confusing a little. String methods are not modifying original object. They return new object. It must be:

var str = "Sonic Free Games";
str = str.replace(/\s+/g, '-').toLowerCase(); //new object assigned to var str

docker : invalid reference format

This also happens when you use development docker compose like the below, in production. You don't want to be building images in production as that breaks the ideology of containers. We should be deploying images:

    build: .
    command: python runserver
      - .:/code
      - "8000:8000"

Change that to use the built image:

    command: /bin/bash
      - "8000:8000" is not a function

If you want to map an object you can use Lodash. Just make sure it's installed via NPM or Yarn and import it.

With Lodash:

Lodash provides a function _.mapValues to map the values and preserve the keys.

_.mapValues({ one: 1, two: 2, three: 3 }, function (v) { return v * 3; });

// => { one: 3, two: 6, three: 9 }

Image overlay on responsive sized images bootstrap

If i understand your question you want to have the overlay just over the image and not cover everything?

I'd set the parent DIV (i renamed in content in the jsfiddle) position to relative, as the overlay should be positioned relative to this div not the window.

  position: relative;

I did some pocking around and updated your fiddle to just have the overlay sized to the img which (I think) is what you want, let me know anyway :)

Get Character value from KeyCode in JavaScript... then trim

In my experience String.fromCharCode(e.keyCode) is unreliable. String.fromCharCode expects unicode charcodes as an argument; e.keyCode returns javascript keycodes. Javascript keycodes and unicode charcodes are not the same thing! In particular, the numberpad keys return a different keycode from the ordinary number keys (since they are different keys) while the same keycode is returned for both upper and lowercase letters (you pressed the same key in both cases), despite them having different charcodes.

For example, the ordinary number key 1 generates an event with keycode 49 while numberpad key 1 (with Numlock on) generates keycode 97. Used with String.fromCharCode we get the following:

String.fromCharCode(49) returns "1"
String.fromCharCode(97) returns "a"

String.fromCharCode expects unicode charcodes, not javascript keycodes. The key a generates an event with a keycode of 65, independentant of the case of the character it would generate (there is also a modifier for if the Shift key is pressed, etc. in the event). The character a has a unicode charcode of 61 while the character A has a charcode of 41 (according to, for example, However, those are hex values, converting to decimal gives us a charcode of 65 for "A" and 97 for "a".[1] This is consistent with what we get from String.fromCharCode for these values.

My own requirement was limited to processing numbers and ordinary letters (accepting or rejecting depending on the position in the string) and letting control characters (F-keys, Ctrl-something) through. Thus I can check for the control characters, if it's not a control character I check against a range and only then do I need to get the actual character. Given I'm not worried about case (I change all letters to uppercase anyway) and have already limited the range of keycodes, I only have to worry about the numberpad keys. The following suffices for that:

String.fromCharCode((96 <= key && key <= 105)? key-48 : key)

More generally, a function to reliably return the character from a charcode would be great (maybe as a jQuery plugin), but I don't have time to write it just now. Sorry.

I'd also mention e.which (if you're using jQuery) which normalizes e.keyCode and e.charCode, so that you don't need to worry about what sort of key was pressed. The problem with combining it with String.fromCharCode remains.

[1] I was confused for a while -. all the docs say that String.fromCharCode expects a unicode charcode, while in practice it seemed to work for ASCII charcodes, but that was I think due to the need to convert to decimal from hex, combined with the fact that ASCII charcodes and unicode decimal charcodes overlap for ordinary latin letters.

how to get the value of css style using jquery

Yes, you're right. With the css() method you can retrieve the desired css value stored in the DOM. You can read more about this at:

But if you want to get its position you can check offset() and position() methods to get it's position.

Jackson: how to prevent field serialization

The easy way is to annotate your getters and setters.

Here is the original example modified to exclude the plain text password, but then annotate a new method that just returns the password field as encrypted text.

class User {

    private String password;

    public void setPassword(String password) {
        this.password = password;

    public String getPassword() {
        return password;

    public String getEncryptedPassword() {
        // encryption logic

How can I use modulo operator (%) in JavaScript?

It's the remainder operator and is used to get the remainder after integer division. Lots of languages have it. For example:

10 % 3 // = 1 ; because 3 * 3 gets you 9, and 10 - 9 is 1.

Apparently it is not the same as the modulo operator entirely.

How to install Cmake C compiler and CXX compiler

Try to install gcc and gcc-c++, as Cmake works smooth with them.


yum install gcc gcc-c++


apt-get install cmake gcc g++


  1. remove 'CMakeCache.txt'
  2. run compilation again.

What's the difference between eval, exec, and compile?

The short answer, or TL;DR

Basically, eval is used to evaluate a single dynamically generated Python expression, and exec is used to execute dynamically generated Python code only for its side effects.

eval and exec have these two differences:

  1. eval accepts only a single expression, exec can take a code block that has Python statements: loops, try: except:, class and function/method definitions and so on.

    An expression in Python is whatever you can have as the value in a variable assignment:

    a_variable = (anything you can put within these parentheses is an expression)
  2. eval returns the value of the given expression, whereas exec ignores the return value from its code, and always returns None (in Python 2 it is a statement and cannot be used as an expression, so it really does not return anything).

In versions 1.0 - 2.7, exec was a statement, because CPython needed to produce a different kind of code object for functions that used exec for its side effects inside the function.

In Python 3, exec is a function; its use has no effect on the compiled bytecode of the function where it is used.

Thus basically:

>>> a = 5
>>> eval('37 + a')   # it is an expression
>>> exec('37 + a')   # it is an expression statement; value is ignored (None is returned)
>>> exec('a = 47')   # modify a global variable as a side effect
>>> a
>>> eval('a = 47')  # you cannot evaluate a statement
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<string>", line 1
    a = 47
SyntaxError: invalid syntax

The compile in 'exec' mode compiles any number of statements into a bytecode that implicitly always returns None, whereas in 'eval' mode it compiles a single expression into bytecode that returns the value of that expression.

>>> eval(compile('42', '<string>', 'exec'))  # code returns None
>>> eval(compile('42', '<string>', 'eval'))  # code returns 42
>>> exec(compile('42', '<string>', 'eval'))  # code returns 42,
>>>                                          # but ignored by exec

In the 'eval' mode (and thus with the eval function if a string is passed in), the compile raises an exception if the source code contains statements or anything else beyond a single expression:

>>> compile('for i in range(3): print(i)', '<string>', 'eval')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<string>", line 1
    for i in range(3): print(i)
SyntaxError: invalid syntax

Actually the statement "eval accepts only a single expression" applies only when a string (which contains Python source code) is passed to eval. Then it is internally compiled to bytecode using compile(source, '<string>', 'eval') This is where the difference really comes from.

If a code object (which contains Python bytecode) is passed to exec or eval, they behave identically, excepting for the fact that exec ignores the return value, still returning None always. So it is possible use eval to execute something that has statements, if you just compiled it into bytecode before instead of passing it as a string:

>>> eval(compile('if 1: print("Hello")', '<string>', 'exec'))

works without problems, even though the compiled code contains statements. It still returns None, because that is the return value of the code object returned from compile.

In the 'eval' mode (and thus with the eval function if a string is passed in), the compile raises an exception if the source code contains statements or anything else beyond a single expression:

>>> compile('for i in range(3): print(i)', '<string>'. 'eval')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<string>", line 1
    for i in range(3): print(i)
SyntaxError: invalid syntax

The longer answer, a.k.a the gory details

exec and eval

The exec function (which was a statement in Python 2) is used for executing a dynamically created statement or program:

>>> program = '''
for i in range(3):
    print("Python is cool")
>>> exec(program)
Python is cool
Python is cool
Python is cool

The eval function does the same for a single expression, and returns the value of the expression:

>>> a = 2
>>> my_calculation = '42 * a'
>>> result = eval(my_calculation)
>>> result

exec and eval both accept the program/expression to be run either as a str, unicode or bytes object containing source code, or as a code object which contains Python bytecode.

If a str/unicode/bytes containing source code was passed to exec, it behaves equivalently to:

exec(compile(source, '<string>', 'exec'))

and eval similarly behaves equivalent to:

eval(compile(source, '<string>', 'eval'))

Since all expressions can be used as statements in Python (these are called the Expr nodes in the Python abstract grammar; the opposite is not true), you can always use exec if you do not need the return value. That is to say, you can use either eval('my_func(42)') or exec('my_func(42)'), the difference being that eval returns the value returned by my_func, and exec discards it:

>>> def my_func(arg):
...     print("Called with %d" % arg)
...     return arg * 2
>>> exec('my_func(42)')
Called with 42
>>> eval('my_func(42)')
Called with 42

Of the 2, only exec accepts source code that contains statements, like def, for, while, import, or class, the assignment statement (a.k.a a = 42), or entire programs:

>>> exec('for i in range(3): print(i)')
>>> eval('for i in range(3): print(i)')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<string>", line 1
    for i in range(3): print(i)
SyntaxError: invalid syntax

Both exec and eval accept 2 additional positional arguments - globals and locals - which are the global and local variable scopes that the code sees. These default to the globals() and locals() within the scope that called exec or eval, but any dictionary can be used for globals and any mapping for locals (including dict of course). These can be used not only to restrict/modify the variables that the code sees, but are often also used for capturing the variables that the executed code creates:

>>> g = dict()
>>> l = dict()
>>> exec('global a; a, b = 123, 42', g, l)
>>> g['a']
>>> l
{'b': 42}

(If you display the value of the entire g, it would be much longer, because exec and eval add the built-ins module as __builtins__ to the globals automatically if it is missing).

In Python 2, the official syntax for the exec statement is actually exec code in globals, locals, as in

>>> exec 'global a; a, b = 123, 42' in g, l

However the alternate syntax exec(code, globals, locals) has always been accepted too (see below).


The compile(source, filename, mode, flags=0, dont_inherit=False, optimize=-1) built-in can be used to speed up repeated invocations of the same code with exec or eval by compiling the source into a code object beforehand. The mode parameter controls the kind of code fragment the compile function accepts and the kind of bytecode it produces. The choices are 'eval', 'exec' and 'single':

  • 'eval' mode expects a single expression, and will produce bytecode that when run will return the value of that expression:

    >>> dis.dis(compile('a + b', '<string>', 'eval'))
      1           0 LOAD_NAME                0 (a)
                  3 LOAD_NAME                1 (b)
                  6 BINARY_ADD
                  7 RETURN_VALUE
  • 'exec' accepts any kinds of python constructs from single expressions to whole modules of code, and executes them as if they were module top-level statements. The code object returns None:

    >>> dis.dis(compile('a + b', '<string>', 'exec'))
      1           0 LOAD_NAME                0 (a)
                  3 LOAD_NAME                1 (b)
                  6 BINARY_ADD
                  7 POP_TOP                             <- discard result
                  8 LOAD_CONST               0 (None)   <- load None on stack
                 11 RETURN_VALUE                        <- return top of stack
  • 'single' is a limited form of 'exec' which accepts a source code containing a single statement (or multiple statements separated by ;) if the last statement is an expression statement, the resulting bytecode also prints the repr of the value of that expression to the standard output(!).

    An if-elif-else chain, a loop with else, and try with its except, else and finally blocks is considered a single statement.

    A source fragment containing 2 top-level statements is an error for the 'single', except in Python 2 there is a bug that sometimes allows multiple toplevel statements in the code; only the first is compiled; the rest are ignored:

    In Python 2.7.8:

    >>> exec(compile('a = 5\na = 6', '<string>', 'single'))
    >>> a

    And in Python 3.4.2:

    >>> exec(compile('a = 5\na = 6', '<string>', 'single'))
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
      File "<string>", line 1
        a = 5
    SyntaxError: multiple statements found while compiling a single statement

    This is very useful for making interactive Python shells. However, the value of the expression is not returned, even if you eval the resulting code.

Thus greatest distinction of exec and eval actually comes from the compile function and its modes.

In addition to compiling source code to bytecode, compile supports compiling abstract syntax trees (parse trees of Python code) into code objects; and source code into abstract syntax trees (the ast.parse is written in Python and just calls compile(source, filename, mode, PyCF_ONLY_AST)); these are used for example for modifying source code on the fly, and also for dynamic code creation, as it is often easier to handle the code as a tree of nodes instead of lines of text in complex cases.

While eval only allows you to evaluate a string that contains a single expression, you can eval a whole statement, or even a whole module that has been compiled into bytecode; that is, with Python 2, print is a statement, and cannot be evalled directly:

>>> eval('for i in range(3): print("Python is cool")')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<string>", line 1
    for i in range(3): print("Python is cool")
SyntaxError: invalid syntax

compile it with 'exec' mode into a code object and you can eval it; the eval function will return None.

>>> code = compile('for i in range(3): print("Python is cool")',
                   '', 'exec')
>>> eval(code)
Python is cool
Python is cool
Python is cool

If one looks into eval and exec source code in CPython 3, this is very evident; they both call PyEval_EvalCode with same arguments, the only difference being that exec explicitly returns None.

Syntax differences of exec between Python 2 and Python 3

One of the major differences in Python 2 is that exec is a statement and eval is a built-in function (both are built-in functions in Python 3). It is a well-known fact that the official syntax of exec in Python 2 is exec code [in globals[, locals]].

Unlike majority of the Python 2-to-3 porting guides seem to suggest, the exec statement in CPython 2 can be also used with syntax that looks exactly like the exec function invocation in Python 3. The reason is that Python 0.9.9 had the exec(code, globals, locals) built-in function! And that built-in function was replaced with exec statement somewhere before Python 1.0 release.

Since it was desirable to not break backwards compatibility with Python 0.9.9, Guido van Rossum added a compatibility hack in 1993: if the code was a tuple of length 2 or 3, and globals and locals were not passed into the exec statement otherwise, the code would be interpreted as if the 2nd and 3rd element of the tuple were the globals and locals respectively. The compatibility hack was not mentioned even in Python 1.4 documentation (the earliest available version online); and thus was not known to many writers of the porting guides and tools, until it was documented again in November 2012:

The first expression may also be a tuple of length 2 or 3. In this case, the optional parts must be omitted. The form exec(expr, globals) is equivalent to exec expr in globals, while the form exec(expr, globals, locals) is equivalent to exec expr in globals, locals. The tuple form of exec provides compatibility with Python 3, where exec is a function rather than a statement.

Yes, in CPython 2.7 that it is handily referred to as being a forward-compatibility option (why confuse people over that there is a backward compatibility option at all), when it actually had been there for backward-compatibility for two decades.

Thus while exec is a statement in Python 1 and Python 2, and a built-in function in Python 3 and Python 0.9.9,

>>> exec("print(a)", globals(), {'a': 42})

has had identical behaviour in possibly every widely released Python version ever; and works in Jython 2.5.2, PyPy 2.3.1 (Python 2.7.6) and IronPython 2.6.1 too (kudos to them following the undocumented behaviour of CPython closely).

What you cannot do in Pythons 1.0 - 2.7 with its compatibility hack, is to store the return value of exec into a variable:

Python 2.7.11+ (default, Apr 17 2016, 14:00:29) 
[GCC 5.3.1 20160413] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> a = exec('print(42)')
  File "<stdin>", line 1
    a = exec('print(42)')
SyntaxError: invalid syntax

(which wouldn't be useful in Python 3 either, as exec always returns None), or pass a reference to exec:

>>> call_later(exec, 'print(42)', delay=1000)
  File "<stdin>", line 1
    call_later(exec, 'print(42)', delay=1000)
SyntaxError: invalid syntax

Which a pattern that someone might actually have used, though unlikely;

Or use it in a list comprehension:

>>> [exec(i) for i in ['print(42)', 'print(foo)']
  File "<stdin>", line 1
    [exec(i) for i in ['print(42)', 'print(foo)']
SyntaxError: invalid syntax

which is abuse of list comprehensions (use a for loop instead!).

How to determine if a string is a number with C++?

I've found the following code to be the most robust (c++11). It catches both integers and floats.

#include <regex>
bool isNumber( std::string token )
    return std::regex_match( token, std::regex( ( "((\\+|-)?[[:digit:]]+)(\\.(([[:digit:]]+)?))?" ) ) );

Default values and initialization in Java

There are a few things to keep in mind while declaring primitive type values.

They are:

  1. Values declared inside a method will not be assigned a default value.
  2. Values declared as instance variables or a static variable will have default values assigned which is 0.

So in your code:

public class Main {
    int instanceVariable;
    static int staticVariable;
    public static void main(String[] args) {
        Main mainInstance = new Main()
        int localVariable;
        int localVariableTwo = 2;
       // System.out.println(localVariable); // Will throw a compilation error

intellij incorrectly saying no beans of type found for autowired repository

Sometimes - in my case that is - the reason is a wrong import. I accidentally imported

import org.jvnet.hk2.annotations.Service

instead of

import org.springframework.stereotype.Service

by blindly accepting the first choice in Idea's suggested imports. Took me a few minutes the first time it happend :-)

Am I trying to connect to a TLS-enabled daemon without TLS?

On Ubuntu after installing lxc-docker you need to add your user to the docker user group:

sudo usermod -a -G docker myusername

This is because of the socket file permissions:

srw-rw---- 1 root docker 0 Mar 20 07:43 /var/run/docker.sock

DO NOT RUN usermod WITHOUT "-a" as suggested in one of the other comments or it will wipe your additional groups setting and will just leave the "docker" group

This is what will happen:

?  ~  id pawel
uid=1000(pawel) gid=1000(pawel) groups=1000(pawel),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),108(lpadmin),124(sambashare),998(docker)
?  ~  usermod -G docker pawel
?  ~  id pawel               
uid=1000(pawel) gid=1000(pawel) groups=1000(pawel),998(docker)

"Cannot allocate an object of abstract type" error

You must have some virtual function declared in one of the parent classes and never implemented in any of the child classes. Make sure that all virtual functions are implemented somewhere in the inheritence chain. If a class's definition includes a pure virtual function that is never implemented, an instance of that class cannot ever be constructed.

How can I get the UUID of my Android phone in an application?

Instead of getting IMEI from TelephonyManager use ANDROID_ID.


This works for each android device irrespective of having telephony.

Error: Cannot access file bin/Debug/... because it is being used by another process

This is pure speculation, and not an answer.

However, I have been having this problem for a while.

I came after a time to suspect an interaction between VS and my AV precautions.

After some playing, it seems that it may have gone away when I modified my antivirus so that everything under the


folder was not included in the real-time protection.

It looks as if the build actually writes the DLL here first, then copies it to the final build location.

How to merge a Series and DataFrame

You could construct a dataframe from the series and then merge with the dataframe. So you specify the data as the values but multiply them by the length, set the columns to the index and set params for left_index and right_index to True:

In [27]:

df.merge(pd.DataFrame(data = [s.values] * len(s), columns = s.index), left_index=True, right_index=True)
   a  b  s1  s2
0  1  3   5   6
1  2  4   5   6

EDIT for the situation where you want the index of your constructed df from the series to use the index of the df then you can do the following:

df.merge(pd.DataFrame(data = [s.values] * len(df), columns = s.index, index=df.index), left_index=True, right_index=True)

This assumes that the indices match the length.

How can I select the row with the highest ID in MySQL?


How to fix "The ConnectionString property has not been initialized"

Referencing the connection string should be done as such:


ConfigurationManager.AppSettings["ConnectionString"] would be looking in the AppSettings for something named ConnectionString, which it would not find. This is why your error message indicated the "ConnectionString" property has not been initialized, because it is looking for an initialized property of AppSettings named ConnectionString.

ConfigurationManager.ConnectionStrings["MyDB"].ConnectionString instructs to look for the connection string named "MyDB".

Here is someone talking about using web.config connection strings

Interfaces vs. abstract classes

Another thing to consider is that, since there is no multiple inheritance, if you want a class to be able to implement/inherit from your interface/abstract class, but inherit from another base class, use an interface.

How to send a POST request from node.js Express?

in your server side the code looks like:

var request = require('request');'/add', function(req, res){
    json: {
    headers: {
        'Content-Type': 'application/json'
  function(error, response, body){
    // console.log(error);
    // console.log(response);
  // res.send("body");

in receiving end server code looks like:'/add', function(req, res){
console.log('received request')
let adunit = new AdUnit(req.body);
.then(game => {
res.status(200).json({'adUnit':'AdUnit is added successfully'})
.catch(err => {
res.status(400).send('unable to save to database');

Schema is just two properties unit_name and unit_price.

Requested registry access is not allowed

You can't write to the HKCR (or HKLM) hives in Vista and newer versions of Windows unless you have administrative privileges. Therefore, you'll either need to be logged in as an Administrator before you run your utility, give it a manifest that says it requires Administrator level (which will prompt the user for Admin login info), or quit changing things in places that non-Administrators shouldn't be playing. :-)

What is a void pointer in C++?

A void* does not mean anything. It is a pointer, but the type that it points to is not known.

It's not that it can return "anything". A function that returns a void* generally is doing one of the following:

  • It is dealing in unformatted memory. This is what operator new and malloc return: a pointer to a block of memory of a certain size. Since the memory does not have a type (because it does not have a properly constructed object in it yet), it is typeless. IE: void.
  • It is an opaque handle; it references a created object without naming a specific type. Code that does this is generally poorly formed, since this is better done by forward declaring a struct/class and simply not providing a public definition for it. Because then, at least it has a real type.
  • It returns a pointer to storage that contains an object of a known type. However, that API is used to deal with objects of a wide variety of types, so the exact type that a particular call returns cannot be known at compile time. Therefore, there will be some documentation explaining when it stores which kinds of objects, and therefore which type you can safely cast it to.

This construct is nothing like dynamic or object in C#. Those tools actually know what the original type is; void* does not. This makes it far more dangerous than any of those, because it is very easy to get it wrong, and there's no way to ask if a particular usage is the right one.

And on a personal note, if you see code that uses void*'s "often", you should rethink what code you're looking at. void* usage, especially in C++, should be rare, used primary for dealing in raw memory.

Move top 1000 lines from text file to a new file using Unix shell commands

Perl approach:

perl -ne 'if($i<1000) { print; } else { print STDERR;}; $i++;' in 1> 2> out && mv in

How to find list of possible words from a letter matrix [Boggle Solver]

Surprisingly, no one attempted a PHP version of this.

This is a working PHP version of John Fouhy's Python solution.

Although I took some pointers from everyone else's answers, this is mostly copied from John.

$boggle = "fxie

$alphabet = str_split(str_replace(array("\n", " ", "\r"), "", strtolower($boggle)));
$rows = array_map('trim', explode("\n", $boggle));
$dictionary = file("C:/dict.txt");
$prefixes = array(''=>'');
$words = array();
$regex = '/[' . implode('', $alphabet) . ']{3,}$/S';
foreach($dictionary as $k=>$value) {
    $value = trim(strtolower($value));
    $length = strlen($value);
    if(preg_match($regex, $value)) {
        for($x = 0; $x < $length; $x++) {
            $letter = substr($value, 0, $x+1);
            if($letter == $value) {
                $words[$value] = 1;
            } else {
                $prefixes[$letter] = 1;

$graph = array();
$chardict = array();
$positions = array();
$c = count($rows);
for($i = 0; $i < $c; $i++) {
    $l = strlen($rows[$i]);
    for($j = 0; $j < $l; $j++) {
        $chardict[$i.','.$j] = $rows[$i][$j];
        $children = array();
        $pos = array(-1,0,1);
        foreach($pos as $z) {
            $xCoord = $z + $i;
            if($xCoord < 0 || $xCoord >= count($rows)) {
            $len = strlen($rows[0]);
            foreach($pos as $w) {
                $yCoord = $j + $w;
                if(($yCoord < 0 || $yCoord >= $len) || ($z == 0 && $w == 0)) {
                $children[] = array($xCoord, $yCoord);
        $graph['None'][] = array($i, $j);
        $graph[$i.','.$j] = $children;

function to_word($chardict, $prefix) {
    $word = array();
    foreach($prefix as $v) {
        $word[] = $chardict[$v[0].','.$v[1]];
    return implode("", $word);

function find_words($graph, $chardict, $position, $prefix, $prefixes, &$results, $words) {
    $word = to_word($chardict, $prefix);
    if(!isset($prefixes[$word])) return false;

    if(isset($words[$word])) {
        $results[] = $word;

    foreach($graph[$position] as $child) {
        if(!in_array($child, $prefix)) {
            $newprefix = $prefix;
            $newprefix[] = $child;
            find_words($graph, $chardict, $child[0].','.$child[1], $newprefix, $prefixes, $results, $words);

$solution = array();
find_words($graph, $chardict, 'None', array(), $prefixes, $solution);

Here is a live link if you want to try it out. Although it takes ~2s in my local machine, it takes ~5s on my webserver. In either case, it is not very fast. Still, though, it is quite hideous so I can imagine the time can be reduced significantly. Any pointers on how to accomplish that would be appreciated. PHP's lack of tuples made the coordinates weird to work with and my inability to comprehend just what the hell is going on didn't help at all.

EDIT: A few fixes make it take less than 1s locally.

Calculate time difference in minutes in SQL Server

Please try as below to get the time difference in hh:mm:ss format

Select StartTime, EndTime, CAST((EndTime - StartTime) as time(0)) 'TotalTime' from [TableName]

Why doesn't TFS get latest get the latest?

WHen I run into this problem with it not getting latest and version mismatches I first do a "Get Specific Version" set it to changeset and put in 1. This will then remove all the files from your local workspace (for that project, folder, file, etc) and it will also have TFS update so that it knows you now have NO VERSION DOWNLOADED. You can then do a "Get Latest" and viola, you will actually have the latest

Body set to overflow-y:hidden but page is still scrollable in Chrome

Try this when you want to "fix" your body's scroll:

jQuery('body').css('height', '100vh').css('overflow-y', 'hidden');

and this when you want to turn it normal again:

jQuery('body').css('height', '').css('overflow-y', '');

How to get all key in JSON object (javascript)

var jsonData = { Name: "Ricardo Vasquez", age: "46", Email: "[email protected]" };

for (x in jsonData) {   
  console.log(x +" => "+ jsonData[x]);  
  alert(x +" => "+  jsonData[x]);  

Jquery validation plugin - TypeError: $(...).validate is not a function

for me, the problem was from require('jquery-validation') i added in the begging of that js file which Validate method used which is necessary as an npm module

unfortunately, when web pack compiles the js files, they aren't in order, so that the validate method is before defining it! and the error comes

so better to use another js file for compiling this library or use local validate method file or even using CDN but in all cases make sure you attached jquery before

Descending order by date filter in AngularJs

And a code example:

<div ng-app>
    <div ng-controller="FooController">
        <ul ng-repeat="item in items | orderBy:'num':true">
            <li>{{item.num}} :: {{item.desc}}</li>

And the JavaScript:

function FooController($scope) {
    $scope.items = [
        {desc: 'a', num: 1},
        {desc: 'b', num: 2},
        {desc: 'c', num: 3},

Will give you:

3 :: c
2 :: b
1 :: a

On JSFiddle:

Detect iPhone/iPad purely by css

I use these:

/* Non-Retina */
@media screen and (-webkit-max-device-pixel-ratio: 1) {

/* Retina */
@media only screen and (-webkit-min-device-pixel-ratio: 1.5),
only screen and (-o-min-device-pixel-ratio: 3/2),
only screen and (min--moz-device-pixel-ratio: 1.5),
only screen and (min-device-pixel-ratio: 1.5) {

/* iPhone Portrait */
@media screen and (max-device-width: 480px) and (orientation:portrait) {

/* iPhone Landscape */
@media screen and (max-device-width: 480px) and (orientation:landscape) {

/* iPad Portrait */
@media screen and (min-device-width: 481px) and (max-device-width: 1024px) and (orientation:portrait) {

/* iPad Landscape */
@media screen and (min-device-width: 481px) and (max-device-width: 1024px) and (orientation:landscape) {

Can dplyr package be used for conditional mutating?

Use ifelse

df %>%
  mutate(g = ifelse(a == 2 | a == 5 | a == 7 | (a == 1 & b == 4), 2,
               ifelse(a == 0 | a == 1 | a == 4 | a == 3 |  c == 4, 3, NA)))

Added - if_else: Note that in dplyr 0.5 there is an if_else function defined so an alternative would be to replace ifelse with if_else; however, note that since if_else is stricter than ifelse (both legs of the condition must have the same type) so the NA in that case would have to be replaced with NA_real_ .

df %>%
  mutate(g = if_else(a == 2 | a == 5 | a == 7 | (a == 1 & b == 4), 2,
               if_else(a == 0 | a == 1 | a == 4 | a == 3 |  c == 4, 3, NA_real_)))

Added - case_when Since this question was posted dplyr has added case_when so another alternative would be:

df %>% mutate(g = case_when(a == 2 | a == 5 | a == 7 | (a == 1 & b == 4) ~ 2,
                            a == 0 | a == 1 | a == 4 | a == 3 |  c == 4 ~ 3,
                            TRUE ~ NA_real_))

Added - arithmetic/na_if If the values are numeric and the conditions (except for the default value of NA at the end) are mutually exclusive, as is the case in the question, then we can use an arithmetic expression such that each term is multiplied by the desired result using na_if at the end to replace 0 with NA.

df %>%
  mutate(g = 2 * (a == 2 | a == 5 | a == 7 | (a == 1 & b == 4)) +
             3 * (a == 0 | a == 1 | a == 4 | a == 3 |  c == 4),
         g = na_if(g, 0))

Inputting a default image in case the src attribute of an html <img> is not valid?

a simple img-element is not very flexible so i combined it with a picture-element. this way no CSS is needed. when an error occurs, all srcset's are set to the fallback version. a broken link image is not showing up. it does not load unneeded image versions. the picture-element supports responsive design and multiple fallbacks for types that are not supported by the browser.

    <source id="s1" srcset="image1_not_supported_by_browser.webp" type="image/webp">
    <source id="s2" srcset="image2_broken_link.png" type="image/png">
    <img src="image3_fallback.jpg" alt="" onerror="this.onerror=null;document.getElementById('s1').srcset=document.getElementById('s2').srcset=this.src;">

What does the percentage sign mean in Python

Modulus operator; gives the remainder of the left value divided by the right value. Like:

3 % 1 would equal zero (since 3 divides evenly by 1)

3 % 2 would equal 1 (since dividing 3 by 2 results in a remainder of 1).

How to grep and replace

Be very careful when using find and sed in a git repo! If you don't exclude the binary files you can end up with this error:

error: bad index file sha1 signature 
fatal: index file corrupt

To solve this error you need to revert the sed by replacing your new_string with your old_string. This will revert your replaced strings, so you will be back to the beginning of the problem.

The correct way to search for a string and replace it is to skip find and use grep instead in order to ignore the binary files:

sed -ri -e "s/old_string/new_string/g" $(grep -Elr --binary-files=without-match "old_string" "/files_dir")

Credits for @hobs

Get all non-unique values (i.e.: duplicate/more than one occurrence) in an array

Yet another way by using underscore. Numbers is the source array and dupes has possible duplicate values.

var itemcounts = _.countBy(numbers, function (n) { return n; });
var dupes = _.reduce(itemcounts, function (memo, item, idx) {
    if (item > 1)
    return memo;
}, []);

Create two-dimensional arrays and access sub-arrays in Ruby

a =

0.upto(a.length-1) do |i|
  0.upto(a.length-1) do |j|
    a[i[j]] = 1

0.upto(a.length-1) do |i|
  0.upto(a.length-1) do |j|
    print a[i[j]] = 1 #It's not a[i][j], but a[i[j]]
  puts "\n"

Delete statement in SQL is very slow

Deleting a lot of rows can be very slow. Try to delete a few at a time, like:

delete top (10) YourTable where col in ('1','2','3','4')
while @@rowcount > 0
    delete top (10) YourTable where col in ('1','2','3','4')

Jquery get form field value

$("form").submit(function(event) {_x000D_
      var firstfield_value  = event.currentTarget[0].value;_x000D_
      var secondfield_value = event.currentTarget[1].value; _x000D_
      event.preventDefault(); _x000D_
<script src=""></script>_x000D_
<form action="" method="post" >_x000D_
<input type="text" name="field1" value="value1">_x000D_
<input type="text" name="field2" value="value2">_x000D_