Programs & Examples On #Adaboost

AdaBoost is a meta machine learning algorithm. It performs several rounds of training in which the best weak classifiers are selected. At the end of each round, the still misclassified training samples are given a higher weight, resulting in more focus on these samples during the next round of selecting a weak classifier.

What does servletcontext.getRealPath("/") mean and when should I use it


The ServletContext#getRealPath() is intented to convert a web content path (the path in the expanded WAR folder structure on the server's disk file system) to an absolute disk file system path.

The "/" represents the web content root. I.e. it represents the web folder as in the below project structure:

 |-- src
 |    :
 |-- web
 |    |-- META-INF
 |    |    `-- MANIFEST.MF
 |    |-- WEB-INF
 |    |    `-- web.xml
 |    |-- index.jsp
 |    `-- login.jsp

So, passing the "/" to getRealPath() would return you the absolute disk file system path of the /web folder of the expanded WAR file of the project. Something like /path/to/server/work/folder/some.war/ which you should be able to further use in File or FileInputStream.

Note that most starters don't seem to see/realize that you can actually pass the whole web content path to it and that they often use

String absolutePathToIndexJSP = servletContext.getRealPath("/") + "index.jsp"; // Wrong!

or even

String absolutePathToIndexJSP = servletContext.getRealPath("") + "index.jsp"; // Wronger!

instead of

String absolutePathToIndexJSP = servletContext.getRealPath("/index.jsp"); // Right!

Don't ever write files in there

Also note that even though you can write new files into it using FileOutputStream, all changes (e.g. new files or edited files) will get lost whenever the WAR is redeployed; with the simple reason that all those changes are not contained in the original WAR file. So all starters who are attempting to save uploaded files in there are doing it wrong.

Moreover, getRealPath() will always return null or a completely unexpected path when the server isn't configured to expand the WAR file into the disk file system, but instead into e.g. memory as a virtual file system.

getRealPath() is unportable; you'd better never use it

Use getRealPath() carefully. There are actually no sensible real world use cases for it. Based on my 20 years of Java EE experience, there has always been another way which is much better and more portable than getRealPath().

If all you actually need is to get an InputStream of the web resource, better use ServletContext#getResourceAsStream() instead, this will work regardless of the way how the WAR is expanded. So, if you for example want an InputStream of index.jsp, then do not do:

InputStream input = new FileInputStream(servletContext.getRealPath("/index.jsp")); // Wrong!

But instead do:

InputStream input = servletContext.getResourceAsStream("/index.jsp"); // Right!

Or if you intend to obtain a list of all available web resource paths, use ServletContext#getResourcePaths() instead.

Set<String> resourcePaths = servletContext.getResourcePaths("/");

You can obtain an individual resource as URL via ServletContext#getResource(). This will return null when the resource does not exist.

URL resource = servletContext.getResource(path);

Or if you intend to save an uploaded file, or create a temporary file, then see the below "See also" links.

See also:

MySQL parameterized queries

Beware of using string interpolation for SQL queries, since it won't escape the input parameters correctly and will leave your application open to SQL injection vulnerabilities. The difference might seem trivial, but in reality it's huge.

Incorrect (with security issues)

c.execute("SELECT * FROM foo WHERE bar = %s AND baz = %s" % (param1, param2))

Correct (with escaping)

c.execute("SELECT * FROM foo WHERE bar = %s AND baz = %s", (param1, param2))

It adds to the confusion that the modifiers used to bind parameters in a SQL statement varies between different DB API implementations and that the mysql client library uses printf style syntax instead of the more commonly accepted '?' marker (used by eg. python-sqlite).

How to get primary key column in Oracle?

Save the following script as something like findPK.sql.

set verify off
accept TABLE_NAME char prompt 'Table name>'

SELECT cols.column_name
FROM all_constraints cons NATURAL JOIN all_cons_columns cols
WHERE cons.constraint_type = 'P' AND table_name = UPPER('&TABLE_NAME');

It can then be called using


Cannot connect to SQL Server named instance from another SQL Server

well after spending about 10 days trying to solve this issue, i finally figured it out today and decide to post the solution

in the start menu, type RUN, open it the in the run box, type SERVICES.MSC, click okay

ensure that these two services are started SQL Server(MSSQLSERVER) SQL Server Vss writer

How to send custom headers with requests in Swagger UI?

Here's a simpler answer for the ASP.NET Core Web Api/Swashbuckle combo, that doesn't require you to register any custom filters. Third time's a charm you know :).

Adding the code below to your Swagger config will cause the Authorize button to appear, allowing you to enter a bearer token to be sent for all requests. Don't forget to enter this token as Bearer <your token here> when asked.

Note that the code below will send the token for any and all requests and operations, which may or may not be what you want.

    services.AddSwaggerGen(c =>

        c.AddSecurityDefinition("Bearer", new ApiKeyScheme()
            Description = "JWT Authorization header using the Bearer scheme. Example: \"Authorization: Bearer {token}\"",
            Name = "Authorization",
            In = "header",
            Type = "apiKey"

        c.AddSecurityRequirement(new Dictionary<string, IEnumerable<string>>
            { "Bearer", new string[] { } }


Via this thread.

YouTube: How to present embed video with sound muted

Try this

<iframe width="420" height="315" src="
HeQ39bLsoTI?autoplay=1&cc_load_policy=1" volume="0" frameborder="0"

don't forget to write volume="0"

Excel 2007 - Compare 2 columns, find matching values

You could fill the C Column with variations on the following formula:


Then C would only contain values that were in A and C.

Eloquent get only one column as an array

I think you can achieve it by using the below code


apt-get for Cygwin?

Update: you can read the more complex answer, which contains more methods and information.

There exists a couple of scripts, which can be used as simple package managers. But as far as I know, none of them allows you to upgrade packages, because it’s not an easy task on Windows since there is not possible to overwrite files in use. So you have to close all Cygwin instances first and then you can use Cygwin’s native setup.exe (which itself does the upgrade via “replace after reboot” method, when files are in use).


The best one for me. Simply because it’s one of the most recent. It works correctly for both platforms - x86 and x86_64. There exists a lot of forks with some additional features. For example the kou1okada fork is one of improved versions.

Cygwin’s setup.exe

It has also command line mode. Moreover it allows you to upgrade all installed packages at once.

setup.exe-x86_64.exe -q --packages=bash,vim

Example use:

setup.exe-x86_64.exe -q --packages="bash,vim"

You can create an alias for easier use, for example:

alias cyg-get="/cygdrive/d/path/to/cygwin/setup-x86_64.exe -q -P"

Then you can for example install the Vim package with:

cyg-get vim

How to show empty data message in Datatables

By default the grid view will take care, just pass empty data set.

How to schedule a task to run when shutting down windows

I had to also enable "Specify maximum wait time for group policy scripts" and "Display instructions in shutdown scripts as they run" to make it work for me as I explain here.

How to echo out the values of this array?

Here is a simple routine for an array of primitive elements:

for ($i = 0; $i < count($mySimpleArray); $i++)
   echo $mySimpleArray[$i] . "\n";

CSS get height of screen resolution

It is not possible to get the height of the screen from CSS. However, using since CSS3 you can use media queries to control the display of the template as per the resolution.

If you want to code on the basis of height using media queries, you can define style-sheet and call it like this.

<link rel="stylesheet" media="screen and (device-height: 600px)" />

How do I wrap text in a pre tag?

Try using

<pre style="white-space:normal;">. 

Or better throw CSS.

How to make the overflow CSS property work with hidden as value

This worked for me

<div style="display: flex; position: absolute; width: 100%;">
  <div style="white-space: nowrap; overflow: hidden;text-overflow: ellipsis;">
    Lorem ipsum dolor sit amet, consectetur adipiscing elit. Integer nec odio. Praesent libero. Sed cursus ante dapibus diam. Sed nisi.

Adding position:absolute to the parent container made it work.

PS: This is for anyone looking for a solution to dynamically truncating text.

EDIT: This was meant to be an answer for this question but since they are related and it could help someone on this question I shall also leave it here instead of deleting it.

Search code inside a Github project

Update January 2013: a brand new search has arrived!, based on

A search for stat within the ruby repo will be expressed as stat repo:ruby/ruby, and will now just workTM.
(the repo name is not case sensitive: test repo:wordpress/wordpress returns the same as test repo:Wordpress/Wordpress)

enter image description here

Will give:

enter image description here

And you have many other examples of search, based on followers, or on forks, or...

Update July 2012 (old days of Lucene search and poor code indexing, combined with broken GUI, kept here for archive):

The search (based on SolrQuerySyntax) is now more permissive and the dreaded "Invalid search query. Try quoting it." is gone when using the default search selector "Everything":)

(I suppose we can all than Tim Pease, which had in one of his objectives "hacking on improved search experiences for all GitHub properties", and I did mention this Stack Overflow question at the time ;) )

Here is an illustration of a grep within the ruby code: it will looks for repos and users, but also for what I wanted to search in the first place: the code!

GitHub more permissive search results

Initial answer and illustration of the former issue (Sept. 2012 => March 2012)

You can use the advanced search GitHub form:

  • Choose Code, Repositories or Users from the drop-down and
  • use the corresponding prefixes listed for that search type.

For instance, Use the repo:username/repo-name directive to limit the search to a code repository.
The initial "Advanced Search" page includes the section:

Code Search:

The Code search will look through all of the code publicly hosted on GitHub. You can also filter by :

  • the language language:
  • the repository name (including the username) repo:
  • the file path path:

So if you select the "Code" search selector, then your query grepping for a text within a repo will work:

Good Search selector

What is incredibly unhelpful from GitHub is that:

  • if you forget to put the right search selector (here "Code"), you will get an error message:
    "Invalid search query. Try quoting it."

Wrong selector for the code filer

  • the error message doesn't help you at all.
    No amount of "quoting it" will get you out of this error.

  • once you get that error message, you don't get the sections reminding you of the right association between the search selectors ("Repositories", "Users" or "Language") and the (right) search filters (here "repo:").
    Any further attempt you do won't display those associations (selectors-filters) back. Only the error message you see above...
    The only way to get back those arrays is by clicking the "Advance Search" icon:

Advance Search Icon on GitHub

  • the "Everything" search selector, which is the default, is actually the wrong one for all of the search filters! Except "language:"...
    (You could imagine/assume that "Everything" would help you to pick whatever search selector actually works with the search filter "repo:", but nope. That would be too easy)

  • you cannot specify the search selector you want through the "Advance Search" field alone!
    (but you can for "language:", even though "Search Language" is another combo box just below the "Search for" 'type' one...)

Wrong search selector

So, the user's experience usually is as follows:

  • you click "Advanced Search", glance over those sections of filters, and notice one you want to use: "repo:"
  • you make a first advanced search "repo:jruby/jruby stat", but with the default Search selector "Everything"
    => FAIL! (and the arrays displaying the association "Selectors-Filters" is gone)
  • you notice that "Search for" selector thingy, select the first choice "Repositories" ("Dah! I want to search within repositories...")
    => FAIL!
  • dejected, you select the next choice of selectors (here, "Users"), without even looking at said selector, just to give it one more try...
    => FAIL!
  • "Screw this, GitHub search is broken! I'm outta here!"
    (GitHub advanced search is actually not broken. Only their GUI is...)

So, to recap, if you want to "grep for something inside a Github project's code", as the OP Ben Humphreys, don't forget to select the "Code" search selector...

What is <=> (the 'Spaceship' Operator) in PHP 7?

According to the RFC that introduced the operator, $a <=> $b evaluates to:

  • 0 if $a == $b
  • -1 if $a < $b
  • 1 if $a > $b

which seems to be the case in practice in every scenario I've tried, although strictly the official docs only offer the slightly weaker guarantee that $a <=> $b will return

an integer less than, equal to, or greater than zero when $a is respectively less than, equal to, or greater than $b

Regardless, why would you want such an operator? Again, the RFC addresses this - it's pretty much entirely to make it more convenient to write comparison functions for usort (and the similar uasort and uksort).

usort takes an array to sort as its first argument, and a user-defined comparison function as its second argument. It uses that comparison function to determine which of a pair of elements from the array is greater. The comparison function needs to return:

an integer less than, equal to, or greater than zero if the first argument is considered to be respectively less than, equal to, or greater than the second.

The spaceship operator makes this succinct and convenient:

$things = [
        'foo' => 5.5,
        'bar' => 'abc'
        'foo' => 7.7,
        'bar' => 'xyz'
        'foo' => 2.2,
        'bar' => 'efg'

// Sort $things by 'foo' property, ascending
usort($things, function ($a, $b) {
    return $a['foo'] <=> $b['foo'];

// Sort $things by 'bar' property, descending
usort($things, function ($a, $b) {
    return $b['bar'] <=> $a['bar'];

More examples of comparison functions written using the spaceship operator can be found in the Usefulness section of the RFC.

install beautiful soup using pip

import os

os.system("pip install beautifulsoup4")


import subprocess

exe = subprocess.Popen("pip install beautifulsoup4")

exe_out = exe.communicate()


JavaScript, Node.js: is Array.forEach asynchronous?

No, it is blocking. Have a look at the specification of the algorithm.

However a maybe easier to understand implementation is given on MDN:

if (!Array.prototype.forEach)
  Array.prototype.forEach = function(fun /*, thisp */)
    "use strict";

    if (this === void 0 || this === null)
      throw new TypeError();

    var t = Object(this);
    var len = t.length >>> 0;
    if (typeof fun !== "function")
      throw new TypeError();

    var thisp = arguments[1];
    for (var i = 0; i < len; i++)
      if (i in t), t[i], i, t);

If you have to execute a lot of code for each element, you should consider to use a different approach:

function processArray(items, process) {
    var todo = items.concat();

    setTimeout(function() {
        if(todo.length > 0) {
            setTimeout(arguments.callee, 25);
    }, 25);

and then call it with:

processArray([many many elements], function () {lots of work to do});

This would be non-blocking then. The example is taken from High Performance JavaScript.

Another option might be web workers.

How to set a text box for inputing password in winforms?

To set a text box for password input:

textBox1.PasswordChar = '*';

you can also change this property in design time by editing properties of the text box.

To show if "Capslock is ON":

using System;  
using System.Windows.Forms;  
if (Control.IsKeyLocked(Keys.CapsLock)) {  
    MessageBox.Show("The Caps Lock key is ON.");  

Filter items which array contains any of given values

Whilst this an old question, I ran into this problem myself recently and some of the answers here are now deprecated (as the comments point out). So for the benefit of others who may have stumbled here:

A term query can be used to find the exact term specified in the reverse index:

  "query": {
   "term" : { "tags" : "a" }

From the documenation

Alternatively you can use a terms query, which will match all documents with any of the items specified in the given array:

  "query": {
   "terms" : { "tags" : ["a", "c"]}

One gotcha to be aware of (which caught me out) - how you define the document also makes a difference. If the field you're searching in has been indexed as a text type then Elasticsearch will perform a full text search (i.e using an analyzed string).

If you've indexed the field as a keyword then a keyword search using a 'non-analyzed' string is performed. This can have a massive practical impact as Analyzed strings are pre-processed (lowercased, punctuation dropped etc.) See (

To avoid these issues, the string field has split into two new types: text, which should be used for full-text search, and keyword, which should be used for keyword search. (

What is the "N+1 selects problem" in ORM (Object-Relational Mapping)?

In my opinion the article written in Hibernate Pitfall: Why Relationships Should Be Lazy is exactly opposite of real N+1 issue is.

If you need correct explanation please refer Hibernate - Chapter 19: Improving Performance - Fetching Strategies

Select fetching (the default) is extremely vulnerable to N+1 selects problems, so we might want to enable join fetching

document.getElementById().value and document.getElementById().checked not working for IE

The code you pasted should work... There must be something else we are not seeing here.

Check this out. Working for me fine on IE7. When you submit you will see the variable passed in the URL.

How to get file creation & modification date/times in Python?

os.stat returns a named tuple with st_mtime and st_ctime attributes. The modification time is st_mtime on both platforms; unfortunately, on Windows, ctime means "creation time", whereas on POSIX it means "change time". I'm not aware of any way to get the creation time on POSIX platforms.

What characters are allowed in an email address?

The answer is (almost) ALL (7-bit ASCII).
If the inclusion rules is "...allowed under some/any/none conditions..."

Just by looking at one of several possible inclusion rules for allowed text in the "domain text" part in RFC 5322 at the top of page 17 we find:

dtext          =   %d33-90 /          ; Printable US-ASCII
                   %d94-126 /         ;  characters not including
                   obs-dtext          ;  "[", "]", or "\"

the only three missing chars in this description are used in domain-literal [], to form a quoted-pair \, and the white space character (%d32). With that the whole range 32-126 (decimal) is used. A similar requirement appear as "qtext" and "ctext". Many control characters are also allowed/used. One list of such control chars appears in page 31 section 4.1 of RFC 5322 as obs-NO-WS-CTL.

obs-NO-WS-CTL  =   %d1-8 /            ; US-ASCII control
                   %d11 /             ;  characters that do not
                   %d12 /             ;  include the carriage
                   %d14-31 /          ;  return, line feed, and
                   %d127              ;  white space characters

All this control characters are allowed as stated at the start of section 3.5:

.... MAY be used, the use of US-ASCII control characters (values
     1 through 8, 11, 12, and 14 through 31) is discouraged ....

And such an inclusion rule is therefore "just too wide". Or, in other sense, the expected rule is "too simplistic".

How to list files using dos commands?

Try dir /b, for bare format.

dir /? will show you documentation of what you can do with the dir command. Here is the output from my Windows 7 machine:

C:\>dir /?
Displays a list of files and subdirectories in a directory.

DIR [drive:][path][filename] [/A[[:]attributes]] [/B] [/C] [/D] [/L] [/N]
  [/O[[:]sortorder]] [/P] [/Q] [/R] [/S] [/T[[:]timefield]] [/W] [/X] [/4]

              Specifies drive, directory, and/or files to list.

  /A          Displays files with specified attributes.
  attributes   D  Directories                R  Read-only files
               H  Hidden files               A  Files ready for archiving
               S  System files               I  Not content indexed files
               L  Reparse Points             -  Prefix meaning not
  /B          Uses bare format (no heading information or summary).
  /C          Display the thousand separator in file sizes.  This is the
              default.  Use /-C to disable display of separator.
  /D          Same as wide but files are list sorted by column.
  /L          Uses lowercase.
  /N          New long list format where filenames are on the far right.
  /O          List by files in sorted order.
  sortorder    N  By name (alphabetic)       S  By size (smallest first)
               E  By extension (alphabetic)  D  By date/time (oldest first)
               G  Group directories first    -  Prefix to reverse order
  /P          Pauses after each screenful of information.
  /Q          Display the owner of the file.
  /R          Display alternate data streams of the file.
  /S          Displays files in specified directory and all subdirectories.
  /T          Controls which time field displayed or used for sorting
  timefield   C  Creation
              A  Last Access
              W  Last Written
  /W          Uses wide list format.
  /X          This displays the short names generated for non-8dot3 file
              names.  The format is that of /N with the short name inserted
              before the long name. If no short name is present, blanks are
              displayed in its place.
  /4          Displays four-digit years

Switches may be preset in the DIRCMD environment variable.  Override
preset switches by prefixing any switch with - (hyphen)--for example, /-W.

My prerelease app has been "processing" for over a week in iTunes Connect, what gives?

I was facing this issue. It solved when I logged in into iTunes Connect in Chrome browser than Safari. My app was in processed state already.

Adding multiple columns AFTER a specific column in MySQL

This works fine for me:


ASP.NET MVC 404 Error Handling

In IIS, you can specify a redirect to "certain" page based on error code. In you example, you can configure 404 - > Your customized 404 error page.

swift UITableView set rowHeight

For setting row height there is separate method:

For Swift 3

func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {
    return 100.0;//Choose your custom row height

Older Swift uses

func tableView(tableView: UITableView, heightForRowAtIndexPath indexPath: NSIndexPath) -> CGFloat {
    return 100.0;//Choose your custom row height

Otherwise you can set row height using:

self.tableView.rowHeight = 44.0

In ViewDidLoad.

Visual Studio 2015 doesn't have cl.exe

For me that have Visual Studio 2015 this works:
Search this in the start menu: Developer Command Prompt for VS2015 and run the program in the search result.
You can now execute your command in it, for example: cl /?

How to configure XAMPP to send mail from localhost?

As in my personal experience I found that very similar thing to Vikas Dwivedi answer will work just fine.

Step 1 (php.ini file)

In php.ini file located in xampp\php\php.ini. Change settings to the following:

 [mail function]
 sendmail_path =":\xampp7\sendmail\sendmail.exe -t"

Turn off other variables under mail funciton by putting ; before them. e.g ;smtp_port=25

Step 2 (sendmail.ini file)

In sendmail.ini located in xampp\sendmail\semdmail.ini change to the following:
 [email protected]

Step 3 (code)

Create a php file and use the following:

    mail($to, "subject", "body", "From: ".$from);


  • You need to restart apache in order for php.ini to reload.
  • you need to activate Google Less secure app access in
  • It might help to run Xampp with Admin permission.

iterating over each character of a String in ruby 1.8.6 (each_char)

I have the same problem. I usually resort to String#split:

"ABCDEFG".split("").each do |i|
  puts i

I guess you could also implement it yourself like this:

class String
  def each_char
    self.split("").each { |i| yield i }

Edit: yet another alternative is String#each_byte, available in Ruby 1.8.6, which returns the ASCII value of each char in an ASCII string:

"ABCDEFG".each_byte do |i|
  puts i.chr # Fixnum#chr converts any number to the ASCII char it represents

How to set the style -webkit-transform dynamically using JavaScript?

If you want to do it via setAttribute you would change the style attribute like so:

element.setAttribute('style','transform:rotate(90deg); -webkit-transform: rotate(90deg)') //etc

This would be helpful if you want to reset all other inline style and only set your needed style properties' values again, BUT in most cases you may not want that. That's why everybody advised to use this: = 'rotate(90deg)'; = 'rotate(90deg)';

The above is equivalent to['transform'] = 'rotate(90deg)';['-webkit-transform'] = 'rotate(90deg)';

Limit text length to n lines using CSS

Currently you can't, but in future you will be able to use text-overflow:ellipis-lastline. Currently it's available with vendor prefix in Opera 10.60+: example

Twitter bootstrap collapse: change display of toggle button

My following JS solution is better than the other approaches here because it ensures that it will always say 'open' when the target is closed, and vice versa.


<a href="#collapseExample" class="btn btn-primary" data-toggle="collapse" data-toggle-secondary="Close">
<div class="collapse" id="collapseExample">
  <div class="well">


$('[data-toggle-secondary]').each(function() {
    var $toggle = $(this);
    var originalText = $toggle.text();
    var secondaryText = $'toggle-secondary');
    var $target = $($toggle.attr('href'));

    $target.on('', function() {
        if ($toggle.text() == originalText) {
        } else {


$('[data-toggle-secondary]').each(function() {_x000D_
    var $toggle = $(this);_x000D_
    var originalText = $toggle.text();_x000D_
    var secondaryText = $'toggle-secondary');_x000D_
    var $target = $($toggle.attr('href'));_x000D_
    $target.on('', function() {_x000D_
        if ($toggle.text() == originalText) {_x000D_
        } else {_x000D_
<script src=""></script>_x000D_
<link href="" rel="stylesheet"/>_x000D_
<script src=""></script>_x000D_
<a href="#collapseExample" class="btn btn-primary" data-toggle="collapse" data-toggle-secondary="Close">_x000D_
<div class="collapse" id="collapseExample">_x000D_
  <div class="well">_x000D_

JS Fiddle

Other benefits of this approach:

  • the code is DRY and reusable
  • each collapse button stays separate
  • you only need to put one change into the HTML: adding the data-toggle-secondary attribute

How do you extract a JAR in a UNIX filesystem with a single command and specify its target directory using the JAR command?

Can't you just change working directory within the python script using os.chdir(target)? I agree, I can't see any way of doing it from the jar command itself.

If you don't want to permanently change directory, then store the current directory (using os.getcwd())in a variable and change back afterwards.

MongoDB what are the default user and password?

In addition with what @Camilo Silva already mentioned, if you want to give free access to create databases, read, write databases, etc, but you don't want to create a root role, you can change the 3rd step with the following:

use admin
    user: "myUserAdmin",
    pwd: "abc123",
    roles: [ { role: "userAdminAnyDatabase", db: "admin" }, 
             { role: "dbAdminAnyDatabase", db: "admin" }, 
             { role: "readWriteAnyDatabase", db: "admin" } ]

Declaring a variable and setting its value from a SELECT query in Oracle

ORA-01422: exact fetch returns more than requested number of rows

if you don't specify the exact record by using where condition, you will get the above exception

     select eid into id from employee where salary=26500;

Postgresql: error "must be owner of relation" when changing a owner object

From the fine manual.

You must own the table to use ALTER TABLE.

Or be a database superuser.

ERROR: must be owner of relation contact

PostgreSQL error messages are usually spot on. This one is spot on.

Send data from javascript to a mysql database

The other posters are correct you cannot connect to MySQL directly from javascript. This is because JavaScript is at client side & mysql is server side.

So your best bet is to use ajax to call a handler as quoted above if you can let us know what language your project is in we can better help you ie php/java/.net

If you project is using php then the example from Merlyn is a good place to start, I would personally use jquery.ajax() to cut down you code and have a better chance of less cross browser issues.

Write output to a text file in PowerShell

The simplest way is to just redirect the output, like so:

Compare-Object $(Get-Content c:\user\documents\List1.txt) $(Get-Content c:\user\documents\List2.txt) > c:\user\documents\diff_output.txt

> will cause the output file to be overwritten if it already exists.
>> will append new text to the end of the output file if it already exists.

What operator is <> in VBA

It is the "not equal" operator, i.e. the equivalent of != in pretty much every other language.

C# winforms combobox dynamic autocomplete

Here is my final solution. It works fine with a large amount of data. I use Timer to make sure the user want find current value. It looks like complex but it doesn't. Thanks to Max Lambertini for the idea.

        private bool _canUpdate = true; 

        private bool _needUpdate = false;       

        //If text has been changed then start timer
        //If the user doesn't change text while the timer runs then start search
        private void combobox1_TextChanged(object sender, EventArgs e)
            if (_needUpdate)
                if (_canUpdate)
                    _canUpdate = false;

        private void UpdateData()
            if (combobox1.Text.Length > 1)
                List<string> searchData = Search.GetData(combobox1.Text);

        //If an item was selected don't start new search
        private void combobox1_SelectedIndexChanged(object sender, EventArgs e)
            _needUpdate = false;

        //Update data only when the user (not program) change something
        private void combobox1_TextUpdate(object sender, EventArgs e)
            _needUpdate = true;

        //While timer is running don't start search
        //timer1.Interval = 1500;
        private void RestartTimer()
            _canUpdate = false;

        //Update data when timer stops
        private void timer1_Tick(object sender, EventArgs e)
            _canUpdate = true;

        //Update combobox with new data
        private void HandleTextChanged(List<string> dataSource)
            var text = combobox1.Text;

            if (dataSource.Count() > 0)
                combobox1.DataSource = dataSource;  

                var sText = combobox1.Items[0].ToString();
                combobox1.SelectionStart = text.Length;
                combobox1.SelectionLength = sText.Length - text.Length;
                combobox1.DroppedDown = true;

                combobox1.DroppedDown = false;
                combobox1.SelectionStart = text.Length;

This solution isn't very cool. So if someone has another solution please share it with me.

Error message: (provider: Shared Memory Provider, error: 0 - No process is on the other end of the pipe.)

In C# and SQL SERVER, we can fix the error by adding Integrated Security = true to the connection string.

Please find the full connection string:

constr = @"Data Source=<Data-Source-Server-Name>;Initial Catalog=<DB-Name>;Integrated Security=true";

Convert NSNumber to int in Objective-C

A tested one-liner:

int number = ((NSNumber*)[dict objectForKey:@"integer"]).intValue;

Why is using "" for array iteration a bad idea?

Since JavaScript elements are saved as standard object properties, it is not advisable to iterate through JavaScript arrays using loops because normal elements and all enumerable properties will be listed.


How to differ sessions in browser-tabs?

You can use link-rewriting to append a unique identifier to all your URLs when starting at a single page (e.g. index.html/jsp/whatever). The browser will use the same cookies for all your tabs so everything you put in cookies will not be unique.

What does asterisk * mean in Python?

I find * useful when writing a function that takes another callback function as a parameter:

def some_function(parm1, parm2, callback, *callback_args):
    a = 1
    b = 2
    callback(a, b, *callback_args)

That way, callers can pass in arbitrary extra parameters that will be passed through to their callback function. The nice thing is that the callback function can use normal function parameters. That is, it doesn't need to use the * syntax at all. Here's an example:

def my_callback_function(a, b, x, y, z):

x = 5
y = 6
z = 7

some_function('parm1', 'parm2', my_callback_function, x, y, z)

Of course, closures provide another way of doing the same thing without requiring you to pass x, y, and z through some_function() and into my_callback_function().

if (select count(column) from table) > 0 then


The oracle tag was not on the question when this answer was offered, and apparently it doesn't work with oracle, but it does work with at least postgres and mysql

No, just use the value directly:

  if (select count(*) from table) > 0 then
     update table
  end if;

Note there is no need for an "else".


You can simply do it all within the update statement (ie no if construct):

update table
set ...
where ...
and exists (select 'x' from table where ...)

How do I parse a URL query parameters, in Javascript?

Today (2.5 years after this answer) you can safely use Array.forEach. As @ricosrealm suggests, decodeURIComponent was used in this function.

function getJsonFromUrl(url) {
  if(!url) url =;
  var query = url.substr(1);
  var result = {};
  query.split("&").forEach(function(part) {
    var item = part.split("=");
    result[item[0]] = decodeURIComponent(item[1]);
  return result;

actually it's not that simple, see the peer-review in the comments, especially:

  • hash based routing (@cmfolio)
  • array parameters (@user2368055)
  • proper use of decodeURIComponent and non-encoded = (@AndrewF)
  • non-encoded + (added by me)

For further details, see MDN article and RFC 3986.

Maybe this should go to codereview SE, but here is safer and regexp-free code:

function getJsonFromUrl(url) {
  if(!url) url = location.href;
  var question = url.indexOf("?");
  var hash = url.indexOf("#");
  if(hash==-1 && question==-1) return {};
  if(hash==-1) hash = url.length;
  var query = question==-1 || hash==question+1 ? url.substring(hash) : 
  var result = {};
  query.split("&").forEach(function(part) {
    if(!part) return;
    part = part.split("+").join(" "); // replace every + with space, regexp-free version
    var eq = part.indexOf("=");
    var key = eq>-1 ? part.substr(0,eq) : part;
    var val = eq>-1 ? decodeURIComponent(part.substr(eq+1)) : "";
    var from = key.indexOf("[");
    if(from==-1) result[decodeURIComponent(key)] = val;
    else {
      var to = key.indexOf("]",from);
      var index = decodeURIComponent(key.substring(from+1,to));
      key = decodeURIComponent(key.substring(0,from));
      if(!result[key]) result[key] = [];
      if(!index) result[key].push(val);
      else result[key][index] = val;
  return result;

This function can parse even URLs like

var url = "?foo%20e[]=a%20a&foo+e[%5Bx%5D]=b&foo e[]=c";
// {"foo e": ["a a",  "c",  "[x]":"b"]}

var obj = getJsonFromUrl(url)["foo e"];
for(var key in obj) { // Array.forEach would skip string keys here
  0 : a a
  1 : c
  [x] : b

create a trusted self-signed SSL cert for localhost (for use with Express/Node)

If you're using node, why not generate them with node? This module seems to be pretty full featured:

Note that I wouldn't generate on the fly. Generate with some kind of build script so you have a consistent certificate and key. Otherwise you'll have to authorize the newly generated self-signed certificate every time.

How to convert minutes to Hours and minutes (hh:mm) in java

You can also use the TimeUnit class. You could define

private static final String FORMAT = "%02d:%02d:%02d";
can have a method like:

public static String parseTime(long milliseconds) {
      return String.format(FORMAT,
              TimeUnit.MILLISECONDS.toMinutes(milliseconds) - TimeUnit.HOURS.toMinutes(
              TimeUnit.MILLISECONDS.toSeconds(milliseconds) - TimeUnit.MINUTES.toSeconds(

Convert an integer to a float number

There is no float type. Looks like you want float64. You could also use float32 if you only need a single-precision floating point value.

package main

import "fmt"

func main() {
    i := 5
    f := float64(i)
    fmt.Printf("f is %f\n", f)

Better way of getting time in milliseconds in javascript?


The skipping is most likely due to garbage collection. Typically garbage collection can be avoided by reusing variables as much as possible, but I can't say specifically what methods you can use to reduce garbage collection pauses.

wget: unable to resolve host address `http'

I have this issue too. I suspect there is an issue with DigitalOcean’s nameservers, so this will likely affect a lot of other people too. Here’s what I’ve done to temporarily get around it - but someone else might be able to advise on a better long-term fix:

  1. Make sure your DNS Resolver config file is writable:

    sudo chmod o+r /etc/resolv.conf

  2. Temporarily change your DNS to use Google’s nameservers instead of DigitalOcean’s:

    sudo nano /etc/resolv.conf

Change the IP address in the file to:

Press CTRL + X to save the file.

This is only a temporary fix as this file is automatically written/updated by the server, however, I’ve not yet worked out what writes to it so that I can update it permanently.

Using "word-wrap: break-word" within a table

table-layout: fixed will get force the cells to fit the table (and not the other way around), e.g.:

<table style="border: 1px solid black; width: 100%; word-wrap:break-word;
              table-layout: fixed;">

Export MySQL data to Excel in PHP

Try the Following Code Please. just only update two values.
1.your_database_name 2.table_name

    $con = new mysqli($host, $username, $password,$dbname); 

        $sql_data="select * from table_name";
    filename = "Webinfopen.xls"; // File Name
    // Download file
    header("Content-Disposition: attachment; filename=\"$filename\"");
    header("Content-Type: application/");

    $flag = false;
    while ($row = mysqli_fetch_assoc($result_data)) {
        if (!$flag) {
            // display field/column names as first row
            echo implode("\t", array_keys($row)) . "\r\n";
            $flag = true;
        echo implode("\t", array_values($row)) . "\r\n";

Subtract days from a DateTime

That error usually occurs when you try to subtract an interval from DateTime.MinValue or you want to add something to DateTime.MaxValue (or you try to instantiate a date outside this min-max interval). Are you sure you're not assigning MinValue somewhere?

LINQ: When to use SingleOrDefault vs. FirstOrDefault() with filtering criteria

In your last example:

var latestCust = db.Customers
.OrderByDescending(x=> x.CreatedOn)
.FirstOrDefault();//Single or First, or doesn't matter?

Yes it does. If you try to use SingleOrDefault() and the query results in more than record you would get and exception. The only time you can safely use SingleOrDefault() is when you are expecting only 1 and only 1 result...

Boolean vs tinyint(1) for boolean values in MySQL

While it's true that bool and tinyint(1) are functionally identical, bool should be the preferred option because it carries the semantic meaning of what you're trying to do. Also, many ORMs will convert bool into your programing language's native boolean type.

Java Byte Array to String to Byte Array

What Arrays.toString() does is create a string representation of each individual byte in your byteArray.

Please check the API documentation Arrays API

To convert your response string back to the original byte array, you have to use split(",") or something and convert it into a collection and then convert each individual item in there to a byte to recreate your byte array.

Laravel 5 show ErrorException file_put_contents failed to open stream: No such file or directory

the solution that worked for me is to just serve the app as admin if you are

  1. on mac or linux use sudo php artisan serve
  2. on windows try to open CMD as an adminstrator and then go to project directory and run php artisan serve

How to change XML Attribute

Here's the beginnings of a parser class to get you started. This ended up being my solution to a similar problem:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Xml.Linq;

namespace XML
    public class Parser

        private string _FilePath = string.Empty;

        private XDocument _XML_Doc = null;

        public Parser(string filePath)
            _FilePath = filePath;
            _XML_Doc = XDocument.Load(_FilePath);

        /// <summary>
        /// Replaces values of all attributes of a given name (attributeName) with the specified new value (newValue) in all elements.
        /// </summary>
        /// <param name="attributeName"></param>
        /// <param name="newValue"></param>
        public void ReplaceAtrribute(string attributeName, string newValue)
            ReplaceAtrribute(string.Empty, attributeName, new List<string> { }, newValue);

        /// <summary>
        /// Replaces values of all attributes of a given name (attributeName) with the specified new value (newValue) in elements with a given name (elementName).
        /// </summary>
        /// <param name="elementName"></param>
        /// <param name="attributeName"></param>
        /// <param name="newValue"></param>
        public void ReplaceAtrribute(string elementName, string attributeName, string newValue)
            ReplaceAtrribute(elementName, attributeName, new List<string> { }, newValue);

        /// <summary>
        /// Replaces values of all attributes of a given name (attributeName) and value (oldValue)  
        /// with the specified new value (newValue) in elements with a given name (elementName).
        /// </summary>
        /// <param name="elementName"></param>
        /// <param name="attributeName"></param>
        /// <param name="oldValue"></param>
        /// <param name="newValue"></param>
        public void ReplaceAtrribute(string elementName, string attributeName, string oldValue, string newValue)
            ReplaceAtrribute(elementName, attributeName, new List<string> { oldValue }, newValue);              

        /// <summary>
        /// Replaces values of all attributes of a given name (attributeName), which has one of a list of values (oldValues), 
        /// with the specified new value (newValue) in elements with a given name (elementName).
        /// If oldValues is empty then oldValues will be ignored.
        /// </summary>
        /// <param name="elementName"></param>
        /// <param name="attributeName"></param>
        /// <param name="oldValues"></param>
        /// <param name="newValue"></param>
        public void ReplaceAtrribute(string elementName, string attributeName, List<string> oldValues, string newValue)
            List<XElement> elements = _XML_Doc.Elements().Descendants().ToList();

            foreach (XElement element in elements)
                if (elementName == string.Empty | element.Name.LocalName.ToString() == elementName)
                    if (element.Attribute(attributeName) != null)

                        if (oldValues.Count == 0 || oldValues.Contains(element.Attribute(attributeName).Value))
                        { element.Attribute(attributeName).Value = newValue; }


        public void SaveChangesToFile()


What is the difference between JavaScript and jQuery?

Javascript is a programming language whereas jQuery is a library to help make writing in javascript easier. It's particularly useful for simply traversing the DOM in an HTML page.

shuffling/permutating a DataFrame in pandas

You can use sklearn.utils.shuffle() (requires sklearn 0.16.1 or higher to support Pandas data frames):

# Generate data
import pandas as pd
df = pd.DataFrame({'A':range(5), 'B':range(5)})
print('df: {0}'.format(df))

# Shuffle Pandas data frame
import sklearn.utils
df = sklearn.utils.shuffle(df)
print('\n\ndf: {0}'.format(df))


df:    A  B
0  0  0
1  1  1
2  2  2
3  3  3
4  4  4

df:    A  B
1  1  1
0  0  0
3  3  3
4  4  4
2  2  2

Then you can use df.reset_index() to reset the index column, if needs to be:

df = df.reset_index(drop=True)
print('\n\ndf: {0}'.format(df)


df:    A  B
0  1  1
1  0  0
2  4  4
3  2  2
4  3  3

Delete all rows in a table based on another table

To Delete table records based on another table

     Delete From Table1 a,Table2 b where


      DELETE FROM Table1


        DELETE Table1
     FROM Table1 t1 INNER JOIN Table2 t2 ON t1.ID = t2.ID;

jQuery Determine if a matched class has a given id

You could also check if the id element is used by doing so:

if(typeof $(.div).attr('id') == undefined){
   //element has no id
} else {
   //element has id selector

I use this method for global dataTables and specific ordered dataTables

How to extract string following a pattern with grep, regex or perl

The regular expression would be:


Then the grouping would be in the \1

Turning Sonar off for certain code

Use //NOSONAR on the line you get warning if it is something you cannot help your code with. It works!

What is output buffering?

I know that this is an old question but I wanted to write my answer for visual learners. I couldn't find any diagrams explaining output buffering on the worldwide-web so I made a diagram myself in Windows mspaint.exe.

If output buffering is turned off, then echo will send data immediately to the Browser.

enter image description here

If output buffering is turned on, then an echo will send data to the output buffer before sending it to the Browser.

enter image description here


To see whether Output buffering is turned on / off please refer to phpinfo at the core section. The output_buffering directive will tell you if Output buffering is on/off.

enter image description here In this case the output_buffering value is 4096 which means that the buffer size is 4 KB. It also means that Output buffering is turned on, on the Web server.


It's possible to turn on/off and change buffer size by changing the value of the output_buffering directive. Just find it in php.ini, change it to the setting of your choice, and restart the Web server. You can find a sample of my php.ini below.

; Output buffering is a mechanism for controlling how much output data
; (excluding headers and cookies) PHP should keep internally before pushing that
; data to the client. If your application's output exceeds this setting, PHP
; will send that data in chunks of roughly the size you specify.
; Turning on this setting and managing its maximum buffer size can yield some
; interesting side-effects depending on your application and web server.
; You may be able to send headers and cookies after you've already sent output
; through print or echo. You also may see performance benefits if your server is
; emitting less packets due to buffered output versus PHP streaming the output
; as it gets it. On production servers, 4096 bytes is a good setting for performance
; reasons.
; Note: Output buffering can also be controlled via Output Buffering Control
;   functions.
; Possible Values:
;   On = Enabled and buffer is unlimited. (Use with caution)
;   Off = Disabled
;   Integer = Enables the buffer and sets its maximum size in bytes.
; Note: This directive is hardcoded to Off for the CLI SAPI
; Default Value: Off
; Development Value: 4096
; Production Value: 4096
output_buffering = 4096

The directive output_buffering is not the only configurable directive regarding Output buffering. You can find other configurable Output buffering directives here:

Example: ob_get_clean()

Below you can see how to capture an echo and manipulate it before sending it to the browser.

// Turn on output buffering  

echo 'Hello World';  // save to output buffer

$output = ob_get_clean();  // Get content from the output buffer, and discard the output buffer ...
$output = strtoupper($output); // manipulate the output  

echo $output;  // send to output stream / Browser

// OUTPUT:  


More info about Output buffer with examples can be found here:

How to get Current Directory?

Code snippets from my CAE project with unicode development environment:

/// @brief Gets current module file path. 
std::string getModuleFilePath() {
    TCHAR buffer[MAX_PATH];
    GetModuleFileName( NULL, buffer, MAX_PATH );
    CT2CA pszPath(buffer);
    std::string path(pszPath);
    std::string::size_type pos = path.find_last_of("\\/");
    return path.substr( 0, pos);

Just use the templete CA2CAEX or CA2AEX which calls the internal API ::MultiByteToWideChar or ::WideCharToMultiByte?

How can I extract a good quality JPEG image from a video file with ffmpeg?

Output the images in a lossless format such as PNG:

ffmpeg.exe -i 10fps.h264 -r 10 -f image2 10fps.h264_%03d.png

Edit/Update: Not quite sure why I originally gave a strange filename example (with a possibly made-up extension).

I have since found that -vsync 0 is simpler than -r 10 because it avoids needing to know the frame rate.

This is something like what I currently use:

mkdir stills
ffmpeg -i my-film.mp4 -vsync 0 -f image2 stills/my-film-%06d.png

To extract only the key frames (which are likely to be of higher quality post-edit):

ffmpeg -skip_frame nokey -i my-film.mp4 -vsync 0 -f image2 stills/my-film-%06d.png

Then use another program (where you can more precisely specify quality, subsampling and DCT method – e.g. GIMP) to convert the PNGs you want to JPEG.

It is possible to obtain slightly sharper images in JPEG format this way than is possible with -qmin 1 -q:v 1 and outputting as JPEG directly from ffmpeg.

Why do we always prefer using parameters in SQL statements?

In addition to other answers need to add that parameters not only helps prevent sql injection but can improve performance of queries. Sql server caching parameterized query plans and reuse them on repeated queries execution. If you not parameterized your query then sql server would compile new plan on each query(with some exclusion) execution if text of query would differ.

More information about query plan caching

SQL Query for Student mark functionality

You just have to partition the problem into some bite-sized steps and solve each one by one

First, get the maximum score in each subject:

select SubjectID, max(MarkRate)
from Mark
group by SubjectID;

Then query who are those that has SubjectID with max MarkRate:

select SubjectID, MarkRate, StudentID
from Mark
where (SubjectID,MarkRate)
  select SubjectID, max(MarkRate)
  from Mark
  group by SubjectID
order by SubjectID, StudentID;

Then obtain the Student's name, instead of displaying just the StudentID:

select SubjectName, MarkRate, StudentName
from Mark
join Student using(StudentID)
join Subject using(SubjectID)
where (SubjectID,MarkRate)
  select SubjectID, max(MarkRate)
  from Mark
  group by SubjectID
order by SubjectName, StudentName

Database vendors' artificial differences aside with regards to joining and correlating results, the basic step is the same; first, partition the problem in a bite-sized parts, and then integrate them as you solved each one of them, so it won't be as confusing.

Sample data:

    (StudentID int, StudentName varchar(6), Details varchar(1));    
    (StudentID, StudentName, Details)
    (1, 'John', 'X'),
    (2, 'Paul', 'X'),
    (3, 'George', 'X'),
    (4, 'Paul', 'X');

    (SubjectID varchar(1), SubjectName varchar(7));    
    (SubjectID, SubjectName)
    ('M', 'Math'),
    ('E', 'English'),
    ('H', 'History');

    (StudentID int, SubjectID varchar(1), MarkRate int);    
    (StudentID, SubjectID, MarkRate)
    (1, 'M', 90),
    (1, 'E', 100),
    (2, 'M', 95),
    (2, 'E', 70),
    (3, 'E', 95),
    (3, 'H', 98),
    (4, 'H', 90),
    (4, 'E', 100);

Live test here:!1/08728/3

IN tuple test is still a join by any other name:

Convert this..

select SubjectName, MarkRate, StudentName
from Mark
join Student using(StudentID)
join Subject using(SubjectID)

where (SubjectID,MarkRate)
  select SubjectID, max(MarkRate)
  from Mark
  group by SubjectID

order by SubjectName, StudentName JOIN:

select SubjectName, MarkRate, StudentName
from Mark
join Student using(StudentID)
join Subject using(SubjectID)

  select SubjectID, max(MarkRate) as MarkRate
  from Mark
  group by SubjectID
  ) as x using(SubjectID,MarkRate)

order by SubjectName, StudentName

Contrast this code with the code immediate it. See how JOIN on independent query look like an IN construct? They almost look the same, and IN was just replaced with JOIN keyword; and the replaced IN keyword with JOIN is in fact longer, you need to alias the independent query's column result(max(MarkRate) AS MarkRate) and also the subquery itself (as x). Anyway, this are just matter of style, I prefer IN clause, as the intent is clearer. Using JOINs merely to reflect the data relationship.

Anyway, here's the query that works on all databases that doesn't support tuple test(IN):

select sb.SubjectName, m.MarkRate, st.StudentName
from Mark as m
join Student as st on st.StudentID = m.StudentID
join Subject as sb on sb.SubjectID = m.SubjectID

  select SubjectID, max(MarkRate) as MaxMarkRate
  from Mark
  group by SubjectID
  ) as x on m.SubjectID = x.SubjectID AND m.MarkRate = x.MaxMarkRate

order by sb.SubjectName, st.StudentName

Live test:!1/08728/4

Displaying a vector of strings in C++

You have to insert the elements using the insert method present in vectors STL, check the below program to add the elements to it, and you can use in the same way in your program.

#include <iostream>
#include <vector>
#include <string.h>

int main ()
  std::vector<std::string> myvector ;
  std::vector<std::string>::iterator it;

   it = myvector.begin();
  std::string myarray [] = { "Hi","hello","wassup" };
  myvector.insert (myvector.begin(), myarray, myarray+3);

  std::cout << "myvector contains:";
  for (it=myvector.begin(); it<myvector.end(); it++)
    std::cout << ' ' << *it;
    std::cout << '\n';

  return 0;

Global keyboard capture in C# application

private void buttonHook_Click(object sender, EventArgs e)
    // Hooks only into specified Keys (here "A" and "B").
    // (***) Use this constructor

    _globalKeyboardHook = new GlobalKeyboardHook(new Keys[] { Keys.A, Keys.B });

    // Hooks into all keys.
    // (***) Or this - not both

    _globalKeyboardHook = new GlobalKeyboardHook();
    _globalKeyboardHook.KeyboardPressed += OnKeyPressed;

And then is working fine.

C-like structures in Python

How about a dictionary?

Something like this:

myStruct = {'field1': 'some val', 'field2': 'some val'}

Then you can use this to manipulate values:

print myStruct['field1']
myStruct['field2'] = 'some other values'

And the values don't have to be strings. They can be pretty much any other object.

Escape double quotes in Java

Escaping the double quotes with backslashes is the only way to do this in Java.

Some IDEs around such as IntelliJ IDEA do this escaping automatically when pasting such a String into a String literal (i.e. between the double quotes surrounding a java String literal)

One other option would be to put the String into some kind of text file that you would then read at runtime

How to install Android SDK on Ubuntu?

install the android SDK for me was not the problem, having the right JRE and JDK was the problem.

To solve this install the JVM 8 (the last fully compatible, for now):

sudo apt-get install openjdk-8-jre

Next use update-alternative to switch to the jre-8 version:

sudo update-alternatives --config java

You can revert JVM version when you want with the same update-alternatives command

Note that you problably have to do the same after this with javac also (now you have only java command at version 8)

first do:

sudo apt-get install openjdk-8-jdk


sudo update-alternatives --config javac

After this you can install android SDK that require this specific Java version

Javascript split regex question

or just (anything but numbers):


Excel Formula to SUMIF date falls in particular month

=SUMPRODUCT( (MONTH($A$2:$A$6)=1) * ($B$2:$B$6) )


  • (MONTH($A$2:$A$6)=1) creates an array of 1 and 0, it's 1 when the month is january, thus in your example the returned array would be [1, 1, 1, 0, 0]

  • SUMPRODUCT first multiplies each value of the array created in the above step with values of the array ($B$2:$B$6), then it sums them. Hence in your example it does this: (1 * 430) + (1 * 96) + (1 * 440) + (0 * 72.10) + (0 * 72.30)

This works also in OpenOffice and Google Spreadsheets

How to convert an integer to a character array using C

Use itoa, as is shown here.

char buf[5];
// Convert 123 to string [buf]
itoa(123, buf, 10);

buf will be a string array as you documented. You might need to increase the size of the buffer.

Integer division with remainder in JavaScript?

I did some speed tests on Firefox.

-100/3             // -33.33..., 0.3663 millisec
Math.floor(-100/3) // -34,       0.5016 millisec
~~(-100/3)         // -33,       0.3619 millisec
(-100/3>>0)        // -33,       0.3632 millisec
(-100/3|0)         // -33,       0.3856 millisec
(-100-(-100%3))/3  // -33,       0.3591 millisec

/* a=-100, b=3 */
a/b                // -33.33..., 0.4863 millisec
Math.floor(a/b)    // -34,       0.6019 millisec
~~(a/b)            // -33,       0.5148 millisec
(a/b>>0)           // -33,       0.5048 millisec
(a/b|0)            // -33,       0.5078 millisec
(a-(a%b))/b        // -33,       0.6649 millisec

The above is based on 10 million trials for each.

Conclusion: Use (a/b>>0) (or (~~(a/b)) or (a/b|0)) to achieve about 20% gain in efficiency. Also keep in mind that they are all inconsistent with Math.floor, when a/b<0 && a%b!=0.

How can I fix the 'Missing Cross-Origin Resource Sharing (CORS) Response Header' webfont issue?

I'm going to assume your host is using C-Panel - and that it's probably HostGator or GoDaddy. In both cases they use C-Panel (in fact, a lot of hosts do) to make the Server administration as easy as possible on you, the end user. Even if you are hosting through someone else - see if you can log in to some kind of admin panel and find an .htaccess file that you can edit. (Note: The period before just means that it's a "hidden" file/directory).

Once you find the htaccess file add the following line:

  1. Header set Access-Control-Allow-Origin "*" Just to see if it works. Warning: Do not use this line on a production server

It should work. If not, call your host and ask them why the line isn't working - they'll probably be able to help you quickly from there.

  1. Once you do have the above working change the * to the address of the requesting domain You may find an issue with canonical addressing (including the www) and if so you may need to configure your host for a redirect. That's a different and smaller bridge to cross though. You'll at least be in the right place.

Reading multiple Scanner inputs

If every input asks the same question, you should use a for loop and an array of inputs:

Scanner dd = new Scanner(;
int[] vars = new int[3];

for(int i = 0; i < vars.length; i++) {
  System.out.println("Enter next var: ");
  vars[i] = dd.nextInt();

Or as Chip suggested, you can parse the input from one line:

Scanner in = new Scanner(;
int[] vars = new int[3];

System.out.println("Enter "+vars.length+" vars: ");
for(int i = 0; i < vars.length; i++)
  vars[i] = in.nextInt();

You were on the right track, and what you did works. This is just a nicer and more flexible way of doing things.

How to check if a file exists from inside a batch file

Try something like the following example, quoted from the output of IF /? on Windows XP:

IF EXIST filename. (
    del filename.
) ELSE (
    echo filename. missing.

You can also check for a missing file with IF NOT EXIST.

The IF command is quite powerful. The output of IF /? will reward careful reading. For that matter, try the /? option on many of the other built-in commands for lots of hidden gems.  

Python equivalent of a given wget command

For Windows and Python 3.x, my two cents contribution about renaming the file on download :

  1. Install wget module : pip install wget
  2. Use wget :
import wget'Url', 'C:\\PathToMyDownloadFolder\\NewFileName.extension')

Truely working command line example :

python -c "import wget;"""", ""C:\\Users\\TestName.TestExtension"")"

Note : 'C:\\PathToMyDownloadFolder\\NewFileName.extension' is not mandatory. By default, the file is not renamed, and the download folder is your local path.

How to write inline if statement for print?

You can use:

print (1==2 and "only if condition true" or "in case condition is false")

Just as well you can keep going like:

print 1==2 and "aa" or ((2==3) and "bb" or "cc")

Real world example:

>>> print "%d item%s found." % (count, (count>1 and 's' or ''))
1 item found.
>>> count = 2
>>> print "%d item%s found." % (count, (count>1 and 's' or ''))
2 items found.

How to get setuptools and easy_install?

For python3 on Ubuntu

 sudo apt-get install python3-setuptools

Can I write or modify data on an RFID tag?

Some RFID chips are read-write, the majority are read-only. You can find out if your chip is read-only by checking the datasheet.

JSON.NET Error Self referencing loop detected for type

In .NET Core 1.0, you can set this as a global setting in your Startup.cs file:

using System.Buffers;
using Microsoft.AspNetCore.Mvc.Formatters;
using Newtonsoft.Json;

// beginning of Startup class

    public void ConfigureServices(IServiceCollection services)
        services.AddMvc(options =>
            options.OutputFormatters.Add(new JsonOutputFormatter(new JsonSerializerSettings(){
                ReferenceLoopHandling = ReferenceLoopHandling.Ignore,
            }, ArrayPool<char>.Shared));

How to write :hover condition for a:before and a:after?

You can also restrict your action to just one class using the right pointed bracket (">"), as I have done in this code:

<!DOCTYPE html>
<html lang="en">
  <meta charset="UTF-8">
  <style type="text/css">
    span {
    a {
    .test1>a:hover span {
    .test1>a:hover:before {

  <div class="test1">
    <a href="#"><span>Google</span></a>
  <div class="test2">
    <a href="#"><span>Apple</span></a>


Note: The hover:before switch works only on the .test1 class

Creating table variable in SQL server 2008 R2

@tableName Table variables are alive for duration of the script running only i.e. they are only session level objects.

To test this, open two query editor windows under sql server management studio, and create table variables with same name but different structures. You will get an idea. The @tableName object is thus temporary and used for our internal processing of data, and it doesn't contribute to the actual database structure.

There is another type of table object which can be created for temporary use. They are #tableName objects declared like similar create statement for physical tables:

Create table #test (Id int, Name varchar(50))

This table object is created and stored in temp database. Unlike the first one, this object is more useful, can store large data and takes part in transactions etc. These tables are alive till the connection is open. You have to drop the created object by following script before re-creating it.

IF OBJECT_ID('tempdb..#test') IS NOT NULL
  DROP TABLE #test 

Hope this makes sense !

How to use both onclick and target="_blank"

The method is prone to cause popup blockers to complain

A better approach is:

Put a form in the webpage with an id

<form action="theUrlToGoTo" method="post" target="yourTarget" id="yourFormName"> </form>

Then use:

function openYourRequiredPage() {
var theForm = document.getElementById("yourFormName");



onclick="Javascript: openYourRequiredPage()"

You can use




As you wish

How to Get a Sublist in C#

With LINQ:

List<string> l = new List<string> { "1", "2", "3" ,"4","5"};
List<string> l2 = l.Skip(1).Take(2).ToList();

If you need foreach, then no need for ToList:

foreach (string s in l.Skip(1).Take(2)){}

Advantage of LINQ is that if you want to just skip some leading element,you can :

List<string> l2 = l.Skip(1).ToList();
foreach (string s in l.Skip(1)){}

i.e. no need to take care of count/length, etc.

Find an element by class name, from a known parent element

var element = $("#parentDiv .myClassNameOfInterest")

calling server side event from html button control

You may use event handler serverclick as below

//cmdAction is the id of HTML button as below

    <form id="form1" runat="server">
        <button type="submit" id="cmdAction" text="Button1" runat="server">

//cs code

public partial class _Default : System.Web.UI.Page
        protected void Page_Load(object sender, EventArgs e)
                cmdAction.ServerClick += new EventHandler(submit_click);  

        protected void submit_click(object sender, EventArgs e)
            Response.Write("HTML Server Button Control");

How to cut first n and last n columns?

You can cut using following ,
-d: delimiter ,-f for fields
\t used for tab separated fields

cut -d$'\t' -f 1-3,7-

Django ChoiceField

First I recommend you as @ChrisHuang-Leaver suggested to define a new file with all the choices you need it there, like

    (1, _("Not relevant")),
    (2, _("Review")),
    (3, _("Maybe relevant")),
    (4, _("Relevant")),
    (5, _("Leading candidate"))
    (1, _("Unread")),
    (2, _("Read"))

Now you need to import them on the models, so the code is easy to understand like this(

from myApp.choices import * 

class Profile(models.Model):
    user = models.OneToOneField(User)    
    status = models.IntegerField(choices=STATUS_CHOICES, default=1)   
    relevance = models.IntegerField(choices=RELEVANCE_CHOICES, default=1)

And you have to import the choices in the too:

from myApp.choices import * 

class CViewerForm(forms.Form):

    status = forms.ChoiceField(choices = STATUS_CHOICES, label="", initial='', widget=forms.Select(), required=True)
    relevance = forms.ChoiceField(choices = RELEVANCE_CHOICES, required=True)

Anyway you have an issue with your template, because you're not using any {{form.field}}, you generate a table but there is no inputs only hidden_fields.

When the user is staff you should generate as many input fields as users you can manage. I think django form is not the best solution for your situation.

I think it will be better for you to use html form, so you can generate as many inputs using the boucle: {% for user in users_list %} and you generate input with an ID related to the user, and you can manage all of them in the view.

C - casting int to char and append char to char

int myInt = 65;

char myChar = (char)myInt;  // myChar should now be the letter A

char[20] myString = {0}; // make an empty string.

myString[0] = myChar;
myString[1] = myChar; // Now myString is "AA"

This should all be found in any intro to C book, or by some basic online searching.

How to log request and response body with Retrofit-Android?

This is not the best way to do it the better answers are above. This is just another way to check it by using Android Logs. Put them all in this helps to catch parsing errors.

 call.enqueue(new Callback<JsonObject>() {
                    public void onResponse(Call<JsonObject> call,
                                           Response<JsonObject> response) {

    // Catching Responses From Retrofit
    Log.d("TAG", "onResponseisSuccessful: "+response.isSuccessful());
    Log.d("TAG", "onResponsebody: "+response.body());
    Log.d("TAG", "onResponseerrorBody: "+response.errorBody());
    Log.d("TAG", "onResponsemessage: "+response.message());
    Log.d("TAG", "onResponsecode: "+response.code());
    Log.d("TAG", "onResponseheaders: "+response.headers());
    Log.d("TAG", "onResponseraw: "+response.raw());
    Log.d("TAG", "onResponsetoString: "+response.toString());


                    public void onFailure(Call<JsonObject> call,
                                          Throwable t) {

Log.d("TAG", "onFailuregetLocalizedMessage: " +t.getLocalizedMessage());
Log.d("TAG", "onFailuregetMessage: " +t.getMessage());
Log.d("TAG", "onFailuretoString: " +t.toString());
Log.d("TAG", "onFailurefillInStackTrace: " +t.fillInStackTrace());
Log.d("TAG", "onFailuregetCause: " +t.getCause());
Log.d("TAG", "onFailuregetStackTrace: " + Arrays.toString(t.getStackTrace()));
Log.d("TAG", "getSuppressed: " + Arrays.toString(t.getSuppressed()));


YouTube API to fetch all videos on a channel

First, you need to get the ID of the playlist that represents the uploads from the user/channel:

You can specify the username with the forUsername={username} param, or specify mine=true to get your own (you need to authenticate first). Include part=contentDetails to see the playlists.


In the result "relatedPlaylists" will include "likes" and "uploads" playlists. Grab that "upload" playlist ID. Also note the "id" is your channelID for future reference.

Next, get a list of videos in that playlist:

Just drop in the playlistId!


Difference between a virtual function and a pure virtual function

You can actually provide implementations of pure virtual functions in C++. The only difference is all pure virtual functions must be implemented by derived classes before the class can be instantiated.

Python error "ImportError: No module named"

Yup. You need the directory to contain the file, which is the file that initializes the package. Here, have a look at this.

The files are required to make Python treat the directories as containing packages; this is done to prevent directories with a common name, such as string, from unintentionally hiding valid modules that occur later on the module search path. In the simplest case, can just be an empty file, but it can also execute initialization code for the package or set the __all__ variable, described later.

How to embed a YouTube channel into a webpage

In order to embed your channel, all you need to do is copy then paste the following code in another web-page.

<script src=""></script>

Make sure to replace the YourChannelName with your actual channel name.

For example: if your channel name were CaliChick94066 your channel embed code would be:

<script src=""></script>

Please look at the following links:

YouTube on your site

Embed YouTube Channel

You just have to name the URL to your channel name. Also you can play with the height and the border color and size. Hope it helps

How to replicate background-attachment fixed on iOS

It has been asked in the past, apparently it costs a lot to mobile browsers, so it's been disabled.

Check this comment by @PaulIrish:

Fixed-backgrounds have huge repaint cost and decimate scrolling performance, which is, I believe, why it was disabled.

you can see workarounds to this in this posts:

Fixed background image with ios7

Fixed body background scrolls with the page on iOS7

What is the difference between 'git pull' and 'git fetch'?

The short and easy answer is that git pull is simply git fetch followed by git merge.

It is very important to note that git pull will automatically merge whether you like it or not. This could, of course, result in merge conflicts. Let's say your remote is origin and your branch is master. If you git diff origin/master before pulling, you should have some idea of potential merge conflicts and could prepare your local branch accordingly.

In addition to pulling and pushing, some workflows involve git rebase, such as this one, which I paraphrase from the linked article:

git pull origin master
git checkout foo-branch
git rebase master
git push origin foo-branch

If you find yourself in such a situation, you may be tempted to git pull --rebase. Unless you really, really know what you are doing, I would advise against that. This warning is from the man page for git-pull, version 2.3.5:

This is a potentially dangerous mode of operation. It rewrites history, which does not bode well when you published that history already. Do not use this option unless you have read git-rebase(1) carefully.

Difference between RUN and CMD in a Dockerfile

There has been enough answers on RUN and CMD. I just want to add a few words on ENTRYPOINT. CMD arguments can be overwritten by command line arguments, while ENTRYPOINT arguments are always used.

This article is a good source of information.

Iterating through a list in reverse order in java

Guava offers Lists#reverse(List) and ImmutableList#reverse(). As in most cases for Guava, the former delegates to the latter if the argument is an ImmutableList, so you can use the former in all cases. These do not create new copies of the list but just "reversed views" of it.


List reversed = ImmutableList.copyOf(myList).reverse();

What is the best JavaScript code to create an img element

oImg.setAttribute('width', '1px');

px is for CSS only. Use either:

oImg.width = '1';

to set a width through HTML, or: = '1px';

to set it through CSS.

Note that old versions of IE don't create a proper image with document.createElement(), and old versions of KHTML don't create a proper DOM Node with new Image(), so if you want to be fully backwards compatible use something like:

// IEWIN boolean previously sniffed through eg. conditional comments

function img_create(src, alt, title) {
    var img = IEWIN ? new Image() : document.createElement('img');
    img.src = src;
    if ( alt != null ) img.alt = alt;
    if ( title != null ) img.title = title;
    return img;

Also be slightly wary of document.body.appendChild if the script may execute as the page is in the middle of loading. You can end up with the image in an unexpected place, or a weird JavaScript error on IE. If you need to be able to add it at load-time (but after the <body> element has started), you could try inserting it at the start of the body using body.insertBefore(body.firstChild).

To do this invisibly but still have the image actually load in all browsers, you could insert an absolutely-positioned-off-the-page <div> as the body's first child and put any tracking/preload images you don't want to be visible in there.

Correct way to set Bearer token with CURL

This is a cURL function that can send or retrieve data. It should work with any PHP app that supports OAuth:

    function jwt_request($token, $post) {

       header('Content-Type: application/json'); // Specify the type of data
       $ch = curl_init(''); // Initialise cURL
       $post = json_encode($post); // Encode the data array into a JSON string
       $authorization = "Authorization: Bearer ".$token; // Prepare the authorisation token
       curl_setopt($ch, CURLOPT_HTTPHEADER, array('Content-Type: application/json' , $authorization )); // Inject the token into the header
       curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
       curl_setopt($ch, CURLOPT_POST, 1); // Specify the request method as POST
       curl_setopt($ch, CURLOPT_POSTFIELDS, $post); // Set the posted fields
       curl_setopt($ch, CURLOPT_FOLLOWLOCATION, 1); // This will follow any redirects
       $result = curl_exec($ch); // Execute the cURL statement
       curl_close($ch); // Close the cURL connection
       return json_decode($result); // Return the received data


Use it within one-way or two-way requests:

$token = "080042cad6356ad5dc0a720c18b53b8e53d4c274"; // Get your token from a cookie or database
$post = array('some_trigger'=>'...','some_values'=>'...'); // Array of data with a trigger
$request = jwt_request($token,$post); // Send or retrieve data

Should operator<< be implemented as a friend or as a member function?

operator<< implemented as a friend function:

#include <iostream>
#include <string>
using namespace std;

class Samp
    int ID;
    string strName; 
    friend std::ostream& operator<<(std::ostream &os, const Samp& obj);
 std::ostream& operator<<(std::ostream &os, const Samp& obj)
        os << obj.ID<< “ ” << obj.strName;
        return os;

int main()
   Samp obj, obj1;
    obj.ID = 100;
    obj.strName = "Hello";
    cout << obj <<endl<< obj1;


100 Hello
100 Hello

This can be a friend function only because the object is on the right hand side of operator<< and argument cout is on the left hand side. So this can't be a member function to the class, it can only be a friend function.

Auto populate columns in one sheet from another sheet

If I understood you right you want to have sheet1!A1 in sheet2!A1, sheet1!A2 in sheet2!A2,...right?

It might not be the best way but you may type the following


and drag it down to the maximum number of rows you expect.

Calling a rest api with username and password - how to

You can also use the RestSharp library for example

var userName = "myuser";
var password = "mypassword";
var host = "";
var client = new RestClient("https://" + host + "/method1");            
client.Authenticator = new HttpBasicAuthenticator(userName, password);            
var request = new RestRequest(Method.POST); 
request.AddHeader("Accept", "application/json");
request.AddHeader("Cache-Control", "no-cache");
request.AddHeader("Content-Type", "application/json");            
IRestResponse response = client.Execute(request);

How to convert password into md5 in jquery?

jQuery doesnt have a method to provide the md5 of a string. So you need to use some external script. There is a plugin called jQuery MD5. and it gives you number of methods to achieve md5. Few of those are

Create (hex-encoded) MD5 hash of a given string value:

var md5 = $.md5('value');

Create (hex-encoded) HMAC-MD5 hash of a given string value and key:

var md5 = $.md5('value', 'key');

Create raw MD5 hash of a given string value:

var md5 = $.md5('value', null, true);

Create raw HMAC-MD5 hash of a given string value and key:

var md5 = $.md5('value', 'key', true);

This might do what you want... Check the snippet here. jQuery MD5

Converting rows into columns and columns into rows using R

Simply use the base transpose function t, wrapped with

final_df <-
     A    B    C    D
a    1    2    3    4
b 0.02 0.04 0.06 0.08
c Aaaa Bbbb Cccc Dddd

Above updated. As docendo discimus pointed out, t returns a matrix. As Mark suggested wrapping it with gets back a data frame instead of a matrix. Thanks!

nginx - client_max_body_size has no effect

I had a similar problem recently and found out, that client_max_body_size 0; can solve such an issue. This will set client_max_body_size to no limit. But the best practice is to improve your code, so there is no need to increase this limit.

AttributeError: 'str' object has no attribute 'strftime'

You should use datetime object, not str.

>>> from datetime import datetime
>>> cr_date = datetime(2013, 10, 31, 18, 23, 29, 227)
>>> cr_date.strftime('%m/%d/%Y')

To get the datetime object from the string, use datetime.datetime.strptime:

>>> datetime.strptime(cr_date, '%Y-%m-%d %H:%M:%S.%f')
datetime.datetime(2013, 10, 31, 18, 23, 29, 227)
>>> datetime.strptime(cr_date, '%Y-%m-%d %H:%M:%S.%f').strftime('%m/%d/%Y')

How to create multidimensional array

very simple

var states = [,];
states[0,0] = tName; 
states[0,1] = '1';
states[1,0] = tName; 
states[2,1] = '1';

. . .

states[n,0] = tName; 
states[n,1] = '1';

Highlight all occurrence of a selected word?

My favorite for doing this is the mark.vim plugin. It allows to highlight several words in different colors simultaneously.

Example Screenshot

What key shortcuts are to comment and uncomment code?

I went to menu: ToolsOptions.


Show command containing and searched: comment

I changed Edit.CommentSelection and assigned Ctrl+/ for commenting.

And I left Ctrl+K then U for the Edit.UncommentSelection.

These could be tweaked to the user's preference as to what key they would prefer for commenting/uncommenting.

How to know when a web page was last updated?

Take a look at

You can find almost everything about the past of a website there.

How to use jquery $.post() method to submit form values

You have to select and send the form data as well:

    $.post("process.php", $("#reg-form").serialize(), function(data) {

Take a look at the documentation for the jQuery serialize method, which encodes the data from the form fields into a data-string to be sent to the server.

Converting JSON to XML in Java

Use the (excellent) JSON-Java library from then

JSONObject json = new JSONObject(str);
String xml = XML.toString(json);

toString can take a second argument to provide the name of the XML root node.

This library is also able to convert XML to JSON using XML.toJSONObject(java.lang.String string)

Check the Javadoc

Link to the the github repository



original post updated with new links

Python Replace \\ with \

path = "C:\\Users\\Programming\\Downloads"
# Replace \\ with a \ along with any random key multiple times
path.replace('\\', '\pppyyyttthhhooonnn')
# Now replace pppyyyttthhhooonnn with a blank string
path.replace("pppyyyttthhhooonnn", "")


#Output... C:\Users\Programming\Downloads

Failed linking file resources

It can also occur if you leave an element with a null or empty attribute in your XML layout file else if your java file's path of objects creation such as specifying improper ID for the object

enter image description here

here frombottom= AnimationUtils.loadAnimation(this,R.anim); in which anim. the id or filename is left blank can lead to such problem.

Vuejs and Vue.set(), update array

As stated before - VueJS simply can't track those operations(array elements assignment). All operations that are tracked by VueJS with array are here. But I'll copy them once again:

  • push()
  • pop()
  • shift()
  • unshift()
  • splice()
  • sort()
  • reverse()

During development, you face a problem - how to live with that :).

push(), pop(), shift(), unshift(), sort() and reverse() are pretty plain and help you in some cases but the main focus lies within the splice(), which allows you effectively modify the array that would be tracked by VueJs. So I can share some of the approaches, that are used the most working with arrays.

You need to replace Item in Array:

// note - findIndex might be replaced with some(), filter(), forEach() 
// or any other function/approach if you need 
// additional browser support, or you might use a polyfill
const index = this.values.findIndex(item => {
          return ( ===
this.values.splice(index, 1, replacementItem)

Note: if you just need to modify an item field - you can do it just by:

this.values[index].itemField = newItemFieldValue

And this would be tracked by VueJS as the item(Object) fields would be tracked.

You need to empty the array:

this.values.splice(0, this.values.length)

Actually you can do much more with this function splice() - w3schools link You can add multiple records, delete multiple records, etc.

Vue.set() and Vue.delete()

Vue.set() and Vue.delete() might be used for adding field to your UI version of data. For example, you need some additional calculated data or flags within your objects. You can do this for your objects, or list of objects(in the loop):

 Vue.set(plan, 'editEnabled', true) //(or this.$set)

And send edited data back to the back-end in the same format doing this before the Axios call:

 Vue.delete(plan, 'editEnabled') //(or this.$delete)

update package.json version automatically

I want to add some clarity to the answers this question got.

Even thought there are some answers here that are tackling properly the problem and providing a solution, they are not the correct ones. The correct answer to this question is to use npm version

Is there a way to edit the file package.json automatically?

Yes, what you can do to make this happen is to run the npm version command when needed, you can read more about it here npm version, but the base usage would be npm version patch and it would add the 3rd digit order on your package.json version (1.0.X)

Would using a git pre-release hook help?

You could configure to run the npm version command on the pre-release hook, as you need, but that depends if that is what you need or not in your CD/CI pipe, but without the npm version command a git pre-release hook can't do anything "easily" with the package.json

The reason why npm version is the correct answer is the following:

  1. If the user is using a folder structure in which he has a package.json he is using npm if he is using npm he has access to the npm scripts.
  2. If he has access to npm scripts he has access to the npm version command.
  3. Using this command he doesn't need to install anything more in his computer or CD/CI pipe which on the long term will reduce the maintainability effort for the project, and will help with the setup

The other answers in which other tools are proposed are incorrect.

gulp-bump works but requires another extra package which could create issues in the long term (point 3 of my answer)

grunt-bump works but requires another extra package which could create issues in the long term (point 3 of my answer)

How do I get the max ID with Linq to Entity?

The best way to get the id of the entity you added is like this:

public int InsertEntity(Entity factor)
    var id =;
    return id;

Case insensitive 'in'

I think you have to write some extra code. For example:

if 'MICHAEL89' in map(lambda name: name.upper(), USERNAMES):

In this case we are forming a new list with all entries in USERNAMES converted to upper case and then comparing against this new list.


As @viraptor says, it is even better to use a generator instead of map. See @Nathon's answer.

Shell script : How to cut part of a string

You can have awk do it all without using cut:

awk '{print substr($7,index($7,"=")+1)}' inputfile

You could use split() instead of substr(index()).

How to set custom ActionBar color / style?

Custom Color:

 <style name="AppTheme" parent="Theme.AppCompat.Light">

                <item name="colorPrimary">@color/ColorPrimary</item>
                <item name="colorPrimaryDark">@color/ColorPrimaryDark</item>
                <!-- Customize your theme here. -->

Custom Style:

 <style name="Theme.AndroidDevelopers" parent="android:style/Theme.Holo.Light">
        <item name="android:selectableItemBackground">@drawable/ad_selectable_background</item>
        <item name="android:popupMenuStyle">@style/MyPopupMenu</item>
        <item name="android:dropDownListViewStyle">@style/MyDropDownListView</item>
        <item name="android:actionBarTabStyle">@style/MyActionBarTabStyle</item>
        <item name="android:actionDropDownStyle">@style/MyDropDownNav</item>
        <item name="android:listChoiceIndicatorMultiple">@drawable/ad_btn_check_holo_light</item>
        <item name="android:listChoiceIndicatorSingle">@drawable/ad_btn_radio_holo_light</item>

For More: Android ActionBar

Get selected value from combo box in C# WPF

Create a ComboBox SelectionChanged Event and set ItemsSource="{Binding}" in the WPF design:


private void comboBox1_SelectionChanged(object sender, SelectionChangedEventArgs e)
    string ob = ((DataRowView)comboBox1.SelectedItem).Row.ItemArray[0].ToString();

How can I access getSupportFragmentManager() in a fragment?

Try this:

private SectionsPagerAdapter mSectionsPagerAdapter = new SectionsPagerAdapter(getActivity().getSupportFragmentManager());

C++ pointer to objects

Simple solution for cast pointer to object

Online demo

class myClass
  void sayHello () {
    cout << "Hello";

int main ()
  myClass* myPointer;
  myClass myObject = myClass(* myPointer); // Cast pointer to object

  return 0;

Printing Even and Odd using two Threads in Java

   private Object lock = new Object();
   private volatile boolean isOdd = false;

    public void generateEvenNumbers(int number) throws InterruptedException {

        synchronized (lock) {
            while (isOdd == false) 
            isOdd = false;

    public void generateOddNumbers(int number) throws InterruptedException {

        synchronized (lock) {
            while (isOdd == true) {
            isOdd = true;

Position absolute and overflow hidden

You just make divs like this:

<div style="width:100px; height: 100px; border:1px solid; overflow:hidden; ">
    <div style="position:inherit; width: 200px; height:200px; background:yellow;">
        <div style="position:absolute; width: 500px; height:50px; background:Pink; z-index: 99;">

I hope this code will help you :)

Is it valid to replace http:// with // in a <script src="http://...">?

Following the gnud's reference, the RFC 3986 section 5.2 says:

If the scheme component is defined, indicating that the reference starts with a scheme name, then the reference is interpreted as an absolute URI and we are done. Otherwise, the reference URI's scheme is inherited from the base URI's scheme component.

So // is correct :-)

Combining two Series into a DataFrame in pandas

A simplification of the solution based on join():

df = a.to_frame().join(b)

Concat all strings inside a List<string> using LINQ

By using LINQ, this should work;

string delimiter = ",";
List<string> items = new List<string>() { "foo", "boo", "john", "doe" };
Console.WriteLine(items.Aggregate((i, j) => i + delimiter + j));

class description:

public class Foo
    public string Boo { get; set; }


class Program
    static void Main(string[] args)
        string delimiter = ",";
        List<Foo> items = new List<Foo>() { new Foo { Boo = "ABC" }, new Foo { Boo = "DEF" },
            new Foo { Boo = "GHI" }, new Foo { Boo = "JKL" } };

        Console.WriteLine(items.Aggregate((i, j) => new Foo{Boo = (i.Boo + delimiter + j.Boo)}).Boo);


And here is my best :)

items.Select(i => i.Boo).Aggregate((i, j) => i + delimiter + j)

pgadmin4 : postgresql application server could not be contacted.

I need to add this here because I've had several issues with this message. If you have recently upgraded to High Sierra you will find the latest (pgadmin 4.20) will keep appearing with the message "Application Server Could Not be Contacted". What this actually means on Macs is that python was unable to configure your environment in ~/.pgadmin

This directory stores all the things you setup and configure and even logs of what was ran on your user copy usage of pgadmin.

The way to fix this issue on High Sierra is down to sqlite3. If you look in that directory you'll see everything is stored in sqlite3 files.

When version 4.20 of pgadmin was released it was shipped with a version later than sqlite3.19 and the problem arises because High Sierra is shipped with sqlite3.19, so to fix this issue, you need to replace the old version of sqlite3 with the latest on your packager.

Now be aware, MacosX+ all use sqlite to store details for the majority of apps on your mac, so you'll need to make sure you do not just wipe the old version but you'll have to have both versions co-existing together in harmony to avoid anything major occurring on your mac.

1) download brew

2) update brew and upgrade brew to make sure it's up-to-date

3) brew install sqlite3

4) mv /usr/bin/sqlite3 /usr/bin/sqlite3.os

5) ln -s /usr/local/Cellar/sqlite/3.21.0/bin/sqlite3 /usr/bin/sqlite3

6) /usr/bin/sqlite3 -version (check version is later than 3.19)

You can now proceed to open up pgadmin as normal

How to edit the legend entry of a chart in Excel?

Left Click on chart. «PivotTable Field List» will appear on right. On the right down quarter of PivotTable Field List (S Values), you see the names of the legends. Left Click on the legend name. Left Click on the «Value field settings». At the top there is «Source Name». You can’t change it. Below there is «Custom Name». Change the Custom Name as you wish. Now the legend name on the chart has the new name you gave.

No generated file in my project

According to my experince i can summarize :

1.The problem is mainly refering to syntax issues that can be occured on xml files.

2.You might copy the AndroidManifest.xml accidently to subfolders .

1.One file is an extension undefined .

After checking all of these Go to Project->Clean or just remove the /bin and /gen folders.

How to check if a file is a valid image file?

format = [".jpg",".png",".jpeg"]
 for (path,dirs,files) in os.walk(path):
     for file in files:
         if file.endswith(tuple(format)):
             print ("Valid",file)

How do I extract Month and Year in a MySQL date and compare them?

There should also be a YEAR().

As for comparing, you could compare dates that are the first days of those years and months, or you could convert the year/month pair into a number suitable for comparison (i.e. bigger = later). (Exercise left to the reader. For hints, read about the ISO date format.)

Or you could use multiple comparisons (i.e. years first, then months).

What is the difference between "Class.forName()" and "Class.forName().newInstance()"?

Maybe an example demonstrating how both methods are used will help you to understand things better. So, consider the following class:

package test;

public class Demo {

    public Demo() {

    public static void main(String[] args) throws Exception {
        Class clazz = Class.forName("test.Demo");
        Demo demo = (Demo) clazz.newInstance();

As explained in its javadoc, calling Class.forName(String) returns the Class object associated with the class or interface with the given string name i.e. it returns test.Demo.class which is affected to the clazz variable of type Class.

Then, calling clazz.newInstance() creates a new instance of the class represented by this Class object. The class is instantiated as if by a new expression with an empty argument list. In other words, this is here actually equivalent to a new Demo() and returns a new instance of Demo.

And running this Demo class thus prints the following output:


The big difference with the traditional new is that newInstance allows to instantiate a class that you don't know until runtime, making your code more dynamic.

A typical example is the JDBC API which loads, at runtime, the exact driver required to perform the work. EJBs containers, Servlet containers are other good examples: they use dynamic runtime loading to load and create components they don't know anything before the runtime.

Actually, if you want to go further, have a look at Ted Neward paper Understanding Class.forName() that I was paraphrasing in the paragraph just above.

EDIT (answering a question from the OP posted as comment): The case of JDBC drivers is a bit special. As explained in the DriverManager chapter of Getting Started with the JDBC API:

(...) A Driver class is loaded, and therefore automatically registered with the DriverManager, in one of two ways:

  1. by calling the method Class.forName. This explicitly loads the driver class. Since it does not depend on any external setup, this way of loading a driver is the recommended one for using the DriverManager framework. The following code loads the class acme.db.Driver:


    If acme.db.Driver has been written so that loading it causes an instance to be created and also calls DriverManager.registerDriver with that instance as the parameter (as it should do), then it is in the DriverManager's list of drivers and available for creating a connection.

  2. (...)

In both of these cases, it is the responsibility of the newly-loaded Driver class to register itself by calling DriverManager.registerDriver. As mentioned, this should be done automatically when the class is loaded.

To register themselves during initialization, JDBC driver typically use a static initialization block like this:

package acme.db;

public class Driver {

    static {
        java.sql.DriverManager.registerDriver(new Driver());


Calling Class.forName("acme.db.Driver") causes the initialization of the acme.db.Driver class and thus the execution of the static initialization block. And Class.forName("acme.db.Driver") will indeed "create" an instance but this is just a consequence of how (good) JDBC Driver are implemented.

As a side note, I'd mention that all this is not required anymore with JDBC 4.0(added as a default package since Java 7) and the new auto-loading feature of JDBC 4.0 drivers. See JDBC 4.0 enhancements in Java SE 6.

Is there any way to return HTML in a PHP function? (without building the return value as a string)

Template File



if (($text = file_get_contents("file.html")) === false) {
    $text = "";

$text = str_replace("{title}", "Title Here", $text);
$text = str_replace("{username}", "Username Here", $text);

then you can echo $text as string

What's the difference between window.location and document.location in JavaScript?

The canonical way to get the current location object is window.location (see this MSDN page from 1996 and the W3C draft from 2006).

Compare this to document.location, which originally only returned the current URL as a string (see this page on MSDN). Probably to avoid confusion, document.location was replaced with document.URL (see here on MSDN), which is also part of DOM Level 1.

As far as I know, all modern browsers map document.location to window.location, but I still prefer window.location as that's what I've used since I wrote my first DHTML.

When increasing the size of VARCHAR column on a large table could there be any problems?

Changing to Varchar(1200) from Varchar(200) should cause you no issue as it is only a metadata change and as SQL server 2008 truncates excesive blank spaces you should see no performance differences either so in short there should be no issues with making the change.

Get index of element as child relative to parent

Yet another way

$("#wizard li").click(function () 


Convert a JSON string to object in Java ME?

Use google GSON library for this

public static <T> T getObject(final String jsonString, final Class<T> objectClass) {  
    Gson gson = new Gson();  
    return gson.fromJson(jsonString, objectClass);  

How can I use optional parameters in a T-SQL stored procedure?

You can do in the following case,

   @FirstName varchar(25) = null,
   @LastName varchar(25) = null,
   @Title varchar(25) = null
      SELECT ID, FirstName, LastName, Title
      FROM tblUsers
        (@FirstName IS NULL OR FirstName = @FirstName) AND
        (@LastNameName IS NULL OR LastName = @LastName) AND
        (@Title IS NULL OR Title = @Title)

however depend on data sometimes better create dynamic query and execute them.

git pull fails "unable to resolve reference" "unable to update local ref"

 # remove the reference file of the branch "lost"
 rm -fv ./.git/refs/remotes/origin/feature/v1.6.9-api-token-bot-reader

 # get all the branches from the master
 git fetch --all

 # git will "know" how-to handle the issue from now on
 #     From
 # * [new branch]      feature/v1.6.9-api-token-bot-reader ->
 # origin/feature/v1.6.9-api-token-bot-reader

 # and push your local changes
 git push

What are the best practices for SQLite on Android?

Inserts, updates, deletes and reads are generally OK from multiple threads, but Brad's answer is not correct. You have to be careful with how you create your connections and use them. There are situations where your update calls will fail, even if your database doesn't get corrupted.

The basic answer.

The SqliteOpenHelper object holds on to one database connection. It appears to offer you a read and write connection, but it really doesn't. Call the read-only, and you'll get the write database connection regardless.

So, one helper instance, one db connection. Even if you use it from multiple threads, one connection at a time. The SqliteDatabase object uses java locks to keep access serialized. So, if 100 threads have one db instance, calls to the actual on-disk database are serialized.

So, one helper, one db connection, which is serialized in java code. One thread, 1000 threads, if you use one helper instance shared between them, all of your db access code is serial. And life is good (ish).

If you try to write to the database from actual distinct connections at the same time, one will fail. It will not wait till the first is done and then write. It will simply not write your change. Worse, if you don’t call the right version of insert/update on the SQLiteDatabase, you won’t get an exception. You’ll just get a message in your LogCat, and that will be it.

So, multiple threads? Use one helper. Period. If you KNOW only one thread will be writing, you MAY be able to use multiple connections, and your reads will be faster, but buyer beware. I haven't tested that much.

Here's a blog post with far more detail and an example app.

Gray and I are actually wrapping up an ORM tool, based off of his Ormlite, that works natively with Android database implementations, and follows the safe creation/calling structure I describe in the blog post. That should be out very soon. Take a look.

In the meantime, there is a follow up blog post:

Also checkout the fork by 2point0 of the previously mentioned locking example:

SQL Server: Cannot insert an explicit value into a timestamp column

If you have a need to copy the exact same timestamp data, change the data type in the destination table from timestamp to binary(8) -- i used varbinary(8) and it worked fine.

This obviously breaks any timestamp functionality in the destination table, so make sure you're ok with that first.

The number of method references in a .dex file cannot exceed 64k API 17

When your app references exceed 65,536 methods, you encounter a build error that indicates your app has reached the limit of the Android build architecture

Multidex support prior to Android 5.0

Versions of the platform prior to Android 5.0 (API level 21) use the Dalvik runtime for executing app code. By default, Dalvik limits apps to a single classes.dex bytecode file per APK. In order to get around this limitation, you can add the multidex support library to your project:

dependencies {
  implementation ''

Multidex support for Android 5.0 and higher

Android 5.0 (API level 21) and higher uses a runtime called ART which natively supports loading multiple DEX files from APK files. Therefore, if your minSdkVersion is 21 or higher, you do not need the multidex support library.

Avoid the 64K limit

  • Remove unused code with ProGuard - Enable code shrinking

Configure multidex in app for

If your minSdkVersion is set to 21 or higher, all you need to do is set multiDexEnabled to true in your module-level build.gradle file

android {
defaultConfig {
    minSdkVersion 21 
    targetSdkVersion 28
    multiDexEnabled true

if your minSdkVersion is set to 20 or lower, then you must use the multidex support library

android {
defaultConfig {
    minSdkVersion 15 
    targetSdkVersion 28
    multiDexEnabled true

dependencies {
  compile ''

Override the Application class, change it to extend MultiDexApplication (if possible) as follows:

public class MyApplication extends MultiDexApplication { ... }

add to the manifest file

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android=""
            android:name="MyApplication" >

print arraylist element?

Here is an updated solution for Java8, using lambdas and streams:


Or, without joining the list into one large string:;

Javascript Get Values from Multiple Select Option Box

Also, change this:

    SelBranchVal = SelBranchVal + "," + InvForm.SelBranch[x].value;


    SelBranchVal = SelBranchVal + InvForm.SelBranch[x].value+ "," ;

The reason is that for the first time the variable SelBranchVal will be empty

List of special characters for SQL LIKE clause

Potential answer for SQL Server

Interesting I just ran a test using LinqPad with SQL Server which should be just running Linq to SQL underneath and it generates the following SQL statement.

Records .Where(r => r.Name.Contains("lkjwer--_~[]"))

-- Region Parameters
DECLARE @p0 VarChar(1000) = '%lkjwer--~_~~~[]%'
-- EndRegion
SELECT [t0].[ID], [t0].[Name]
WHERE [t0].[Name] LIKE @p0 ESCAPE '~'

So I haven't tested it yet but it looks like potentially the ESCAPE '~' keyword may allow for automatic escaping of a string for use within a like expression.

Hide a EditText & make it visible by clicking a menu

protected void onCreate(Bundle savedInstanceState) {
    setContentView(R.layout.waist2height); {
        final EditText edit = (EditText)findViewById(;          
        final RadioButton rb1 = (RadioButton) findViewById(;
        final RadioButton rb2 = (RadioButton) findViewById(;                       
        else if(rb2.isChecked()){               

What is the difference between `` and `Enum.toString()`?

Use toString() when you want to present information to a user (including a developer looking at a log). Never rely in your code on toString() giving a specific value. Never test it against a specific string. If your code breaks when someone correctly changes the toString() return, then it was already broken.

If you need to get the exact name used to declare the enum constant, you should use name() as toString may have been overridden.

Installing SciPy and NumPy using pip

On windows python 3.5, I managed to install scipy by using conda not pip:

conda install scipy

How do you use variables in a simple PostgreSQL script?

For use variables in for example alter table:

DO $$ 
DECLARE name_pk VARCHAR(200);
select constraint_name
from information_schema.table_constraints
where table_schema = 'schema_name'
      and table_name = 'table_name'
      and constraint_type = 'PRIMARY KEY' INTO name_pk;
IF (name_pk := '') THEN
EXECUTE 'ALTER TABLE schema_name.table_name DROP CONSTRAINT ' || name_pk;

How are echo and print different in PHP?

They are:

  • print only takes one parameter, while echo can have multiple parameters.
  • print returns a value (1), so can be used as an expression.
  • echo is slightly faster.

How can I send an inner <div> to the bottom of its parent <div>?

Here is way to avoid absolute divs and tables if you know parent's height:

<div class="parent">
    <div class="child"> <a href="#">Home</a>


.parent {
    border: 1px solid black;
.child {
    display: inline-block;
    border: 1px solid red;



How do I get SUM function in MySQL to return '0' if no values are found?

Use COALESCE to avoid that outcome.

FROM   table
WHERE  ...

To see it in action, please see this sql fiddle:!2/d1542/3/0

More Information:

Given three tables (one with all numbers, one with all nulls, and one with a mixture):

SQL Fiddle

MySQL 5.5.32 Schema Setup:

  val   INT


  val   INT


  val   INT


Query 1:

SELECT  'foo'                   as table_name,
        'mixed null/non-null'   as description,
        21                      as expected_sum,
        COALESCE(SUM(val), 0)   as actual_sum
FROM    foo

SELECT  'bar'                   as table_name,
        'all non-null'          as description,
        21                      as expected_sum,
        COALESCE(SUM(val), 0)   as actual_sum
FROM    bar

SELECT  'baz'                   as table_name,
        'all null'              as description,
        0                       as expected_sum,
        COALESCE(SUM(val), 0)   as actual_sum
FROM    baz


|        foo | mixed null/non-null |           21 |         21 |
|        bar |        all non-null |           21 |         21 |
|        baz |            all null |            0 |          0 |

Priority queue in .Net

The following implementation of a PriorityQueue uses SortedSet from the System library.

using System;
using System.Collections.Generic;

namespace CDiggins
    interface IPriorityQueue<T, K> where K : IComparable<K>
        bool Empty { get; }
        void Enqueue(T x, K key);
        void Dequeue();
        T Top { get; }

    class PriorityQueue<T, K> : IPriorityQueue<T, K> where K : IComparable<K>
        SortedSet<Tuple<T, K>> set;

        class Comparer : IComparer<Tuple<T, K>> {
            public int Compare(Tuple<T, K> x, Tuple<T, K> y) {
                return x.Item2.CompareTo(y.Item2);

        PriorityQueue() { set = new SortedSet<Tuple<T, K>>(new Comparer()); }
        public bool Empty { get { return set.Count == 0;  } }
        public void Enqueue(T x, K key) { set.Add(Tuple.Create(x, key)); }
        public void Dequeue() { set.Remove(set.Max); }
        public T Top { get { return set.Max.Item1; } }

How can I pass data from Flask to JavaScript in a template?

Working answers are already given but I want to add a check that acts as a fail-safe in case the flask variable is not available. When you use:

var myVariable = {{ flaskvar | tojson }};

if there is an error that causes the variable to be non existent, resulting errors may produce unexpected results. To avoid this:

{% if flaskvar is defined and flaskvar %}
var myVariable = {{ flaskvar | tojson }};
{% endif %}

Practical uses for AtomicInteger

The primary use of AtomicInteger is when you are in a multithreaded context and you need to perform thread safe operations on an integer without using synchronized. The assignation and retrieval on the primitive type int are already atomic but AtomicInteger comes with many operations which are not atomic on int.

The simplest are the getAndXXX or xXXAndGet. For instance getAndIncrement() is an atomic equivalent to i++ which is not atomic because it is actually a short cut for three operations: retrieval, addition and assignation. compareAndSet is very useful to implements semaphores, locks, latches, etc.

Using the AtomicInteger is faster and more readable than performing the same using synchronization.

A simple test:

public synchronized int incrementNotAtomic() {
    return notAtomic++;

public void performTestNotAtomic() {
    final long start = System.currentTimeMillis();
    for (int i = 0 ; i < NUM ; i++) {
    System.out.println("Not atomic: "+(System.currentTimeMillis() - start));

public void performTestAtomic() {
    final long start = System.currentTimeMillis();
    for (int i = 0 ; i < NUM ; i++) {
    System.out.println("Atomic: "+(System.currentTimeMillis() - start));

On my PC with Java 1.6 the atomic test runs in 3 seconds while the synchronized one runs in about 5.5 seconds. The problem here is that the operation to synchronize (notAtomic++) is really short. So the cost of the synchronization is really important compared to the operation.

Beside atomicity AtomicInteger can be use as a mutable version of Integer for instance in Maps as values.

how do I loop through a line from a csv file in powershell

Import-Csv $path | Foreach-Object { 

    foreach ($property in $_.PSObject.Properties)
        doSomething $property.Name, $property.Value


Stock ticker symbol lookup API

Your best bets are probably going with one of the other lookup services (still screen-scraping), and checking whether they don't require CAPTCHAs.

The last appears the least likely to require a CAPTCHA at any point, but it's worth checking all three.

How to solve "Connection reset by peer: socket write error"?

The socket has been closed by the client (browser).

A bug in your code:

byte[] outputByte=new byte[4096];

The last packet read, then write may have a length < 4096, so I suggest:

byte[] outputByte=new byte[4096];
int len;
while(( len =, 0, 4096 )) > 0 ) {
   output.write( outputByte, 0, len );

It's not your question, but it's my answer... ;-)

Parse error: syntax error, unexpected [

Are you using php 5.4 on your local? the render line is using the new way of initializing arrays. Try replacing ["title" => "Welcome "] with array("title" => "Welcome ")

What is a correct MIME type for .docx, .pptx, etc.?

Just look at MDN Web Docs.

Here is a list of MIME types, associated by type of documents, ordered by their common extensions:

Common MIME types

Exception thrown in catch and finally clause

class MyExc1 extends Exception {}
class MyExc2 extends Exception {}
class MyExc3 extends MyExc2 {}

public class C1 {
    public static void main(String[] args) throws Exception {
        try {
            System.out.print("TryA L1\n");
            System.out.print("TryB L1\n");
        catch (Exception i) {
            System.out.print("Catch L1\n");                
        finally {
            System.out.print("Finally L1\n");
            throw new MyExc1();

    static void q() throws Exception {
        try {
            System.out.print("TryA L2\n");
            System.out.print("TryB L2\n");
        catch (Exception y) {
            System.out.print("Catch L2\n");
            throw new MyExc2();  
        finally {
            System.out.print("Finally L2\n");
            throw new Exception();

    static void q2() throws Exception {
        throw new MyExc1();


TryA L1
TryA L2
Catch L2
Finally L2
Catch L1
Finally L1        
Exception in thread "main" MyExc1 at C1.main(

CSS3 selector :first-of-type with class name?

You can do this by selecting every element of the class that is the sibling of the same class and inverting it, which will select pretty much every element on the page, so then you have to select by the class again.


    :not(.bar ~ .bar).bar {
        color: red;
    <div class="foo"></div>
    <div class="bar"></div> <!-- Only this will be selected -->
    <div class="foo"></div>
    <div class="bar"></div>
    <div class="foo"></div>
    <div class="bar"></div>

Resource u'tokenizers/punkt/english.pickle' not found

Simple will not solve this issue. I tried the below and it worked for me:

in the nltk folder create a tokenizers folder and copy your punkt folder into tokenizers folder.

This will work.! the folder structure needs to be as shown in the picture

How do I add an "Add to Favorites" button or link on my website?

This code is the corrected version of iambriansreed's answer:

<script type="text/javascript">
    $(function() {
        $("#bookmarkme").click(function() {
            // Mozilla Firefox Bookmark
            if ('sidebar' in window && 'addPanel' in window.sidebar) { 
            } else if( /*@cc_on!@*/false) { // IE Favorite
            } else { // webkit - safari/chrome
                alert('Press ' + (navigator.userAgent.toLowerCase().indexOf('mac') != - 1 ? 'Command/Cmd' : 'CTRL') + ' + D to bookmark this page.');

Python constructors and __init__

coonstructors are called automatically when you create a new object, thereby "constructing" the object. The reason you can have more than one init is because names are just references in python, and you are allowed to change what each variable references whenever you want (hence dynamic typing)

def func(): #now func refers to an empty funcion
func=5      #now func refers to the number 5
def func():
    print "something"    #now func refers to a different function

in your class definition, it just keeps the later one

How to redirect stderr to null in cmd.exe

Your DOS command 2> nul

Read page Using command redirection operators. Besides the "2>" construct mentioned by Tanuki Software, it lists some other useful combinations.

AngularJS : ng-click not working

It just happend to me. I solved the problem by tracing backward from the point ng-click is coded. Found out that an extra


was placed in the html to prematurely close the div block that contains the ng-click.

Removed the extra


then everything is working fine.

Index Error: list index out of range (Python)

Generally it means that you are providing an index for which a list element does not exist.

E.g, if your list was [1, 3, 5, 7], and you asked for the element at index 10, you would be well out of bounds and receive an error, as only elements 0 through 3 exist.

XAMPP Start automatically on Windows 7 startup

Try following Steps for Apache

  • Go to your XAMPP installation folder. Right-click xampp-control.exe. Click "Run as administrator"
  • Stop Apache service action port
  • Tick this (in snapshot) check box. It will ask if you want to install as service. Click "Yes".
  • Go to Windows Services by typing Window + R, then typing services.msc

  • Enter a new service name as Apache2 (or similar)

  • Set it as automatic, if you want it to run as startup.

Repeat the steps for the MySQL service

enter image description here

Get name of current class?

I think, it should be like this:

    class foo():
        input = get_input(__qualname__)

How can I wait for set of asynchronous callback functions?

You haven't been very specific with your code, so I'll make up a scenario. Let's say you have 10 ajax calls and you want to accumulate the results from those 10 ajax calls and then when they have all completed you want to do something. You can do it like this by accumulating the data in an array and keeping track of when the last one has finished:

Manual Counter

var ajaxCallsRemaining = 10;
var returnedData = [];

for (var i = 0; i < 10; i++) {
    doAjax(whatever, function(response) {
        // success handler from the ajax call

        // save response

        // see if we're done with the last ajax call
        if (ajaxCallsRemaining <= 0) {
            // all data is here now
            // look through the returnedData and do whatever processing 
            // you want on it right here

Note: error handling is important here (not shown because it's specific to how you're making your ajax calls). You will want to think about how you're going to handle the case when one ajax call never completes, either with an error or gets stuck for a long time or times out after a long time.

jQuery Promises

Adding to my answer in 2014. These days, promises are often used to solve this type of problem since jQuery's $.ajax() already returns a promise and $.when() will let you know when a group of promises are all resolved and will collect the return results for you:

var promises = [];
for (var i = 0; i < 10; i++) {
$.when.apply($, promises).then(function() {
    // returned data is in arguments[0][0], arguments[1][0], ... arguments[9][0]
    // you can process it here
}, function() {
    // error occurred

ES6 Standard Promises

As specified in kba's answer: if you have an environment with native promises built-in (modern browser or node.js or using babeljs transpile or using a promise polyfill), then you can use ES6-specified promises. See this table for browser support. Promises are supported in pretty much all current browsers, except IE.

If doAjax() returns a promise, then you can do this:

var promises = [];
for (var i = 0; i < 10; i++) {
Promise.all(promises).then(function() {
    // returned data is in arguments[0], arguments[1], ... arguments[n]
    // you can process it here
}, function(err) {
    // error occurred

If you need to make a non-promise async operation into one that returns a promise, you can "promisify" it like this:

function doAjax(...) {
    return new Promise(function(resolve, reject) {
        someAsyncOperation(..., function(err, result) {
            if (err) return reject(err);

And, then use the pattern above:

var promises = [];
for (var i = 0; i < 10; i++) {
Promise.all(promises).then(function() {
    // returned data is in arguments[0], arguments[1], ... arguments[n]
    // you can process it here
}, function(err) {
    // error occurred

Bluebird Promises

If you use a more feature rich library such as the Bluebird promise library, then it has some additional functions built in to make this easier:

 var doAjax = Promise.promisify(someAsync);
 var someData = [...], doAjax).then(function(results) {
     // all ajax results here
 }, function(err) {
     // some error here

Fixed digits after decimal with f-strings

When it comes to float numbers, you can use format specifiers:



  • value is any expression that evaluates to a number
  • width specifies the number of characters used in total to display, but if value needs more space than the width specifies then the additional space is used.
  • precision indicates the number of characters used after the decimal point

What you are missing is the type specifier for your decimal value. In this link, you an find the available presentation types for floating point and decimal.

Here you have some examples, using the f (Fixed point) presentation type:

# notice that it adds spaces to reach the number of characters specified by width
In [1]: f'{1 + 3 * 1.5:10.3f}'
Out[1]: '     5.500'

# notice that it uses more characters than the ones specified in width
In [2]: f'{3000 + 3 ** (1 / 2):2.1f}' 
Out[2]: '3001.7'

In [3]: f'{1.2345 + 4 ** (1 / 2):9.6f}'
Out[3]: ' 3.234500'

# omitting width but providing precision will use the required characters to display the number with the the specified decimal places
In [4]: f'{1.2345 + 3 * 2:.3f}' 
Out[4]: '7.234'

# not specifying the format will display the number with as many digits as Python calculates
In [5]: f'{1.2345 + 3 * 0.5}'
Out[5]: '2.7344999999999997'

What do the python file extensions, .pyc .pyd .pyo stand for?

  • .py - Regular script
  • .py3 - (rarely used) Python3 script. Python3 scripts usually end with ".py" not ".py3", but I have seen that a few times
  • .pyc - compiled script (Bytecode)
  • .pyo - optimized pyc file (As of Python3.5, Python will only use pyc rather than pyo and pyc)
  • .pyw - Python script to run in Windowed mode, without a console; executed with pythonw.exe
  • .pyx - Cython src to be converted to C/C++
  • .pyd - Python script made as a Windows DLL
  • .pxd - Cython script which is equivalent to a C/C++ header
  • .pxi - MyPy stub
  • .pyi - Stub file (PEP 484)
  • .pyz - Python script archive (PEP 441); this is a script containing compressed Python scripts (ZIP) in binary form after the standard Python script header
  • .pywz - Python script archive for MS-Windows (PEP 441); this is a script containing compressed Python scripts (ZIP) in binary form after the standard Python script header
  • .py[cod] - wildcard notation in ".gitignore" that means the file may be ".pyc", ".pyo", or ".pyd".
  • .pth - a path configuration file; its contents are additional items (one per line) to be added to sys.path. See site module.

A larger list of additional Python file-extensions (mostly rare and unofficial) can be found at

How do I find my host and username on mysql?

Default user for MySQL is "root", and server "localhost".

Center a H1 tag inside a DIV

<div id="AlertDiv" style="width:600px;height:400px;border:SOLID 1px;">
    <h1 style="width:100%;height:10%;text-align:center;position:relative;top:40%;">Yes</h1>

You can try the code here:

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

You have two options with simple and idiomatic Typescript:

  1. Use index type
DNATranscriber: { [char: string]: string } = {
  G: "C",
  C: "G",
  T: "A",
  A: "U",

This is the index signature the error message is talking about. Reference

  1. Type each property:
DNATranscriber: { G: string; C: string; T: string; A: string } = {
  G: "C",
  C: "G",
  T: "A",
  A: "U",

Java 6 Unsupported major.minor version 51.0

add jdk8 or higher version at JAVA_HOME and path.

add JAVA_HOME add C:\ProgramFiles\Java\jdk1.8.0_201

For Path =>

add %MAVEN_HOME%\bin

and finally restart your pc.

Getting the last element of a list

some_list[-1] is the shortest and most Pythonic.

In fact, you can do much more with this syntax. The some_list[-n] syntax gets the nth-to-last element. So some_list[-1] gets the last element, some_list[-2] gets the second to last, etc, all the way down to some_list[-len(some_list)], which gives you the first element.

You can also set list elements in this way. For instance:

>>> some_list = [1, 2, 3]
>>> some_list[-1] = 5 # Set the last element
>>> some_list[-2] = 3 # Set the second to last element
>>> some_list
[1, 3, 5]

Note that getting a list item by index will raise an IndexError if the expected item doesn't exist. This means that some_list[-1] will raise an exception if some_list is empty, because an empty list can't have a last element.

What is the use of the @Temporal annotation in Hibernate?

I use Hibernate 5.2 and @Temporal is not required anymore.,, time.LocalDate are stored into DB with appropriate datatype as Date/timestamp.

How to exit a 'git status' list in a terminal?

If you are facing this?

enter image description here Sometimes it is possible that while writing in Gitbash you get into > and you just can not get out of that.
It happens with me quite often while I type ' by mistake in Gitbash(See in the image).

How to solve this in Mac?

control + C

I have not checked it in Windows. But if it does please edit that in my answer.

jQuery - Getting the text value of a table cell in the same row as a clicked element

You want .children() instead (documentation here):


Print the stack trace of an exception

Throwable.printStackTrace(..) can take a PrintWriter or PrintStream argument:

} catch (Exception ex) {

That said, consider using a logger interface like SLF4J with an logging implementation like LOGBack or log4j.