Programs & Examples On #Antialiasing

The technique of minimizing the distortion artifacts when representing a high-resolution image at a lower resolution

Webfont Smoothing and Antialiasing in Firefox and Opera

Well, Firefox does not support something like that.

In the reference page from Mozilla specifies font-smooth as CSS property controls the application of anti-aliasing when fonts are rendered, but this property has been removed from this specification and is currently not on the standard track.

This property is only supported in Webkit browsers.

If you want an alternative you can check this:

css transform, jagged edges in chrome

You might be able to mask the jagging using blurred box-shadows. Using -webkit-box-shadow instead of box-shadow will make sure it doesn't affect non-webkit browsers. You might want to check Safari and the mobile webkit browsers though.

The result is somewhat better, but still a lot less good then with the other browsers:

with box shadow (underside)

HTML5 Canvas and Anti-aliasing

It's now 2018, and we finally have cheap ways to do something around it...

Indeed, since the 2d context API now has a filter property, and that this filter property can accept SVGFilters, we can build an SVGFilter that will keep only fully opaque pixels from our drawings, and thus eliminate the default anti-aliasing.

So it won't deactivate antialiasing per se, but provides a cheap way both in term of implementation and of performances to remove all semi-transparent pixels while drawing.

I am not really a specialist of SVGFilters, so there might be a better way of doing it, but for the example, I'll use a <feComponentTransfer> node to grab only fully opaque pixels.

var ctx = canvas.getContext('2d');_x000D_
ctx.fillStyle = '#ABEDBE';_x000D_
ctx.fillStyle = 'black';_x000D_
ctx.font = '14px sans-serif';_x000D_
ctx.textAlign = 'center';_x000D_
// first without filter_x000D_
ctx.fillText('no filter', 60, 20);_x000D_
// then with filter_x000D_
ctx.setTransform(1, 0, 0, 1, 120, 0);_x000D_
ctx.filter = 'url(#remove-alpha)';_x000D_
// and do the same ops_x000D_
ctx.fillText('no alpha', 60, 20);_x000D_
// to remove the filter_x000D_
ctx.filter = 'none';_x000D_
function drawArc() {_x000D_
  ctx.arc(60, 80, 50, 0, Math.PI * 2);_x000D_
function drawTriangle() {_x000D_
  ctx.moveTo(60, 150);_x000D_
  ctx.lineTo(110, 230);_x000D_
  ctx.lineTo(10, 230);_x000D_
// unrelated_x000D_
// simply to show a zoomed-in version_x000D_
var zCtx = zoomed.getContext('2d');_x000D_
zCtx.imageSmoothingEnabled = false;_x000D_
canvas.onmousemove = function drawToZoommed(e) {_x000D_
  var x = e.pageX - this.offsetLeft,_x000D_
    y = e.pageY - this.offsetTop,_x000D_
    w = this.width,_x000D_
    h = this.height;_x000D_
  zCtx.drawImage(this, x-w/6,y-h/6,w, h, 0,0,w*3, h*3);_x000D_
<svg width="0" height="0" style="position:absolute;z-index:-1;">_x000D_
    <filter id="remove-alpha" x="0" y="0" width="100%" height="100%">_x000D_
        <feFuncA type="discrete" tableValues="0 1"></feFuncA>_x000D_
<canvas id="canvas" width="250" height="250" ></canvas>_x000D_
<canvas id="zoomed" width="250" height="250" ></canvas>

And for the ones that don't like to append an <svg> element in their DOM, you can also save it as an external svg file and set the filter property to path/to/svg_file.svg#remove-alpha.

How to apply font anti-alias effects in CSS?

Short answer: You can't.

CSS does not have techniques which affect the rendering of fonts in the browser; only the system can do that.

Obviously, text sharpness can easily be achieved with pixel-dense screens, but if you're using a normal PC that's gonna be hard to achieve.

There are some newer fonts that are smooth but at the sacrifice of it appearing somewhat blurry (look at most of Adobe's fonts, for example). You can also find some smooth-but-blurry-by-design fonts at Google Fonts, however.

There are some new CSS3 techniques for font rendering and text effects though the consistency, performance, and reliability of these techniques vary so largely to the point where you generally shouldn't rely on them too much.

Use jQuery to scroll to the bottom of a div with lots of text

//note: use of stop function to prevent animation build-ups if called repeatedly
//subtracting container height brings scrollTo position to container bottom
scrollUp = function() {
    $("#scroller").stop().animate({ scrollTop: 0 }, "slow");

scrollDown = function() {
    var scroller = $('#scroller');
    var height = scroller[0].scrollHeight - $(scroller).height();

    $(scroller).stop().animate({ scrollTop: height }, "slow");

Print Combining Strings and Numbers

The other answers explain how to produce a string formatted like in your example, but if all you need to do is to print that stuff you could simply write:

first = 10
second = 20
print "First number is", first, "and second number is", second

How can I parse a YAML file in Python

If you have YAML that conforms to the YAML 1.2 specification (released 2009) then you should use ruamel.yaml (disclaimer: I am the author of that package). It is essentially a superset of PyYAML, which supports most of YAML 1.1 (from 2005).

If you want to be able to preserve your comments when round-tripping, you certainly should use ruamel.yaml.

Upgrading @Jon's example is easy:

import ruamel.yaml as yaml

with open("example.yaml") as stream:
    except yaml.YAMLError as exc:

Use safe_load() unless you really have full control over the input, need it (seldom the case) and know what you are doing.

If you are using pathlib Path for manipulating files, you are better of using the new API ruamel.yaml provides:

from ruamel.yaml import YAML
from pathlib import Path

path = Path('example.yaml')
yaml = YAML(typ='safe')
data = yaml.load(path)

ArrayAdapter in android to create simple listview

For your question answer is is int: The id of the TextView within the layout resource to be populated.

ArrayAdapter has so many constructors with different number of arguments I'm mention some of them

ArrayAdapter(Context context, int resource)
ArrayAdapter(Context context, int resource, int textViewResourceId)
ArrayAdapter(Context context, int resource, T[] objects)
ArrayAdapter(Context context, int resource, int textViewResourceId, T[] objects)
ArrayAdapter(Context context, int resource, List<T> objects)
ArrayAdapter(Context context, int resource, int textViewResourceId, List<T> objects)

Now you can understand each and every constructor is different and they used different list of arguments.

And simple answer is you can use ArrayAdapter with text view inside a target xml file or without. It is doesn't matter. And you not need specify text view id you can use it without. But you may need to go with some advance option with your simple list view you must go with a text view.!

Here sample example

ArrayAdapter adapter = new ArrayAdapter<String>(this,R.layout.ListView,StringArray);
ListView listView = (ListView) findViewById(;

This is also a valid code you can use with much more clear.

What is the idiomatic Go equivalent of C's ternary operator?

As pointed out (and hopefully unsurprisingly), using if+else is indeed the idiomatic way to do conditionals in Go.

In addition to the full blown var+if+else block of code, though, this spelling is also used often:

index := val
if val <= 0 {
    index = -val

and if you have a block of code that is repetitive enough, such as the equivalent of int value = a <= b ? a : b, you can create a function to hold it:

func min(a, b int) int {
    if a <= b {
        return a
    return b


value := min(a, b)

The compiler will inline such simple functions, so it's fast, more clear, and shorter.

How to delete the contents of a folder?

Use the method bellow to remove the contents of a directory, not the directory itself:

import os
import shutil

def remove_contents(path):
    for c in os.listdir(path):
        full_path = os.path.join(path, c)
        if os.path.isfile(full_path):

Uncaught ReferenceError: jQuery is not defined

set this jquery min js

script src=""

in wp-admin/admin-header.php

setTimeout / clearTimeout problems

This works well. It's a manager I've made to handle hold events. Has events for hold, and for when you let go.

function onUserHold(element, func, hold, clearfunc) {
    //var holdTime = 0;
    var holdTimeout;

    element.addEventListener('mousedown', function(e) {
        holdTimeout = setTimeout(function() {
            holdTime = 0;
        }, hold);

    element.addEventListener('mouseup', clearTime);
    element.addEventListener('mouseout', clearTime);

    function clearTime() {
        holdTime = 0;
        if(clearfunc) {

The element parameter is the one which you hold. The func parameter fires when it holds for a number of milliseconds specified by the parameter hold. The clearfunc param is optional and if it is given, it will get fired if the user lets go or leaves the element. You can also do some work-arounds to get the features you want. Enjoy! :)

How to filter a dictionary according to an arbitrary condition function?

points_small = dict(filter(lambda (a,(b,c)): b<5 and c < 5, points.items()))

How to redirect siteA to siteB with A or CNAME records

It's probably best/easiest to set up a 301 redirect. No DNS hacking required.

Should __init__() call the parent class's __init__()?

In Anon's answer:
"If you need something from super's __init__ to be done in addition to what is being done in the current class's __init__ , you must call it yourself, since that will not happen automatically"

It's incredible: he is wording exactly the contrary of the principle of inheritance.

It is not that "something from super's __init__ (...) will not happen automatically" , it is that it WOULD happen automatically, but it doesn't happen because the base-class' __init__ is overriden by the definition of the derived-clas __init__

So then, WHY defining a derived_class' __init__ , since it overrides what is aimed at when someone resorts to inheritance ??

It's because one needs to define something that is NOT done in the base-class' __init__ , and the only possibility to obtain that is to put its execution in a derived-class' __init__ function.
In other words, one needs something in base-class' __init__ in addition to what would be automatically done in the base-classe' __init__ if this latter wasn't overriden.
NOT the contrary.

Then, the problem is that the desired instructions present in the base-class' __init__ are no more activated at the moment of instantiation. In order to offset this inactivation, something special is required: calling explicitly the base-class' __init__ , in order to KEEP , NOT TO ADD, the initialization performed by the base-class' __init__ . That's exactly what is said in the official doc:

An overriding method in a derived class may in fact want to extend rather than simply replace the base class method of the same name. There is a simple way to call the base class method directly: just call BaseClassName.methodname(self, arguments).

That's all the story:

  • when the aim is to KEEP the initialization performed by the base-class, that is pure inheritance, nothing special is needed, one must just avoid to define an __init__ function in the derived class

  • when the aim is to REPLACE the initialization performed by the base-class, __init__ must be defined in the derived-class

  • when the aim is to ADD processes to the initialization performed by the base-class, a derived-class' __init__ must be defined , comprising an explicit call to the base-class __init__

What I feel astonishing in the post of Anon is not only that he expresses the contrary of the inheritance theory, but that there have been 5 guys passing by that upvoted without turning a hair, and moreover there have been nobody to react in 2 years in a thread whose interesting subject must be read relatively often.

How to print a string multiple times?

The question is a bit unclear can't you just repeat the for loop?


for i in a:
    print i

for i in a:
    print i

The backend version is not supported to design database diagrams or tables

This is commonly reported as an error due to using the wrong version of SSMS(Sql Server Management Studio). Use the version designed for your database version. You can use the command select @@version to check which version of sql server you are actually using. This version is reported in a way that is easier to interpret than that shown in the Help About in SSMS.

Using a newer version of SSMS than your database is generally error-free, i.e. backward compatible.

In C, how should I read a text file and print all strings

You can use fgets and limit the size of the read string.

char *fgets(char *str, int num, FILE *stream);

You can change the while in your code to:

while (fgets(str, 100, file)) /* printf("%s", str) */;

Get index of a key in json

What you are after are numerical indexes in the way classic arrays work, however there is no such thing with json object/associative arrays.

"key1", "key2" themeselves are the indexes and there is no numerical index associated with them. If you want to have such functionality you have to assiciate them yourself.

How to refresh a page with jQuery by passing a parameter to URL

Concision counts: I prefer window.location = "?single"; or window.location += "?single";

ORA-12154 could not resolve the connect identifier specified

This error (and also ORA-6413: Connection not open) can also be caused by parentheses in the application executable path and a bug in the or lower oracle client libraries.

You should either upgrade your oracle client library or change the executable path.

Further details see:

How to remove entity with ManyToMany relationship in JPA (and corresponding join table rows)?

For what its worth, I am using EclipseLink 2.3.2.v20111125-r10461 and if I have a @ManyToMany unidirectional relationship I observe the problem that you describe. However, if I change it to be a bi-directional @ManyToMany relationship I am able to delete an entity from the non-owning side and the JOIN table is updated appropriately. This is all without the use of any cascade attributes.

Namespace not recognized (even though it is there)

In my case, the referenced dll was build in higher version of .Net Framework. After I added the reference, I could use it. But as soon as I did a build, the 'missing reference' error will pop up. I refresh the dll the error will go but it would never build. This post made me check the framework version and thus I could resolve it by building the referenced project in same version.

Incrementing a date in JavaScript

None of the examples in this answer seem to work with Daylight Saving Time adjustment days. On those days, the number of hours in a day are not 24 (they are 23 or 25, depending on if you are "springing forward" or "falling back".)

The below AddDays javascript function accounts for daylight saving time:

function addDays(date, amount) {
  var tzOff = date.getTimezoneOffset() * 60 * 1000,
      t = date.getTime(),
      d = new Date(),

  t += (1000 * 60 * 60 * 24) * amount;

  tzOff2 = d.getTimezoneOffset() * 60 * 1000;
  if (tzOff != tzOff2) {
    var diff = tzOff2 - tzOff;
    t += diff;

  return d;

Here are the tests I used to test the function:

    var d = new Date(2010,10,7);
    var d2 = AddDays(d, 1);
    document.write(d.toString() + "<br />" + d2.toString());

    d = new Date(2010,10,8);
    d2 = AddDays(d, -1)
    document.write("<hr /><br />" +  d.toString() + "<br />" + d2.toString());

    d = new Date('Sun Mar 27 2011 01:59:00 GMT+0100 (CET)');
    d2 = AddDays(d, 1)
    document.write("<hr /><br />" +  d.toString() + "<br />" + d2.toString());

    d = new Date('Sun Mar 28 2011 01:59:00 GMT+0100 (CET)');
    d2 = AddDays(d, -1)
    document.write("<hr /><br />" +  d.toString() + "<br />" + d2.toString());

How to use a parameter in ExecStart command line?

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

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

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

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

So, you may start it like:

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

For systemd it will different instances:

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

It also mean great possibility enable and disable it separately.

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

Quicksort: Choosing the pivot

Don't try and get too clever and combine pivoting strategies. If you combined median of 3 with random pivot by picking the median of the first, last and a random index in the middle, then you'll still be vulnerable to many of the distributions which send median of 3 quadratic (so its actually worse than plain random pivot)

E.g a pipe organ distribution (1,2,3...N/2..3,2,1) first and last will both be 1 and the random index will be some number greater than 1, taking the median gives 1 (either first or last) and you get an extermely unbalanced partitioning.

How can I override inline styles with external CSS?

!important, after your CSS declaration.

div {
   color: blue !important; 

   /* This Is Now Working */

"Specified argument was out of the range of valid values"

It seems that you are trying to get 5 items out of a collection with 5 items. Looking at your code, it seems you're starting at the second value in your collection at position 1. Collections are zero-based, so you should start with the item at index 0. Try this:

TextBox box1 = (TextBox)Gridview1.Rows[i].Cells[0].FindControl("txt_type");
TextBox box2 = (TextBox)Gridview1.Rows[i].Cells[1].FindControl("txt_total");
TextBox box3 = (TextBox)Gridview1.Rows[i].Cells[2].FindControl("txt_max");
TextBox box4 = (TextBox)Gridview1.Rows[i].Cells[3].FindControl("txt_min");
TextBox box5 = (TextBox)Gridview1.Rows[i].Cells[4].FindControl("txt_rate");

How to scale a UIImageView proportionally?

imageView.contentMode = UIViewContentModeScaleAspectFill;
imageView.clipsToBounds = YES;

How to convert JSON object to an Typescript array?

You have a JSON object that contains an Array. You need to access the array results. Change your code to: = res.json().results

How can I call a shell command in my Perl script?

How to run a shell script from a Perl program

1. Using system system($command, @arguments);

For example:

system("sh", "", "--help" );

system("sh --help");

System will execute the $command with @arguments and return to your script when finished. You may check $! for certain errors passed to the OS by the external application. Read the documentation for system for the nuances of how various invocations are slightly different.

2. Using exec

This is very similar to the use of system, but it will terminate your script upon execution. Again, read the documentation for exec for more.

3. Using backticks or qx//

my $output = ` --option`;

my $output = qx/ --option/;

The backtick operator and it's equivalent qx//, excute the command and options inside the operator and return that commands output to STDOUT when it finishes.

There are also ways to run external applications through creative use of open, but this is advanced use; read the documentation for more.

cleanest way to skip a foreach if array is empty

I think the best approach here is to plan your code so that $items is always an array. The easiest solution is to initialize it at the top of your code with $items=array(). This way it will represent empty array even if you don't assign any value to it.

All other solutions are quite dirty hacks to me.

Emulator: ERROR: x86 emulation currently requires hardware acceleration

Right click on your my computer icon and the CPU will be listed on the properties page. Or open device manager and look at the CPU. It must be an Intel processor that supports VT and NX bit (XD) - you can check your CPU # at
Also make sure hyperV off bcdedit /set hypervisorlaunchtype off
XD bit is on bcdedit /set nx AlwaysOn
Use the installer from
If you're using Avast, disable "Enable hardware-assisted virtualization" under: Settings > Troubleshooting. Restart the PC and try to run the HAXM installation again

How to find and return a duplicate value in array

a = ["A", "B", "C", "B", "A"]
a.detect{ |e| a.count(e) > 1 }

I know this isn't very elegant answer, but I love it. It's beautiful one liner code. And works perfectly fine unless you need to process huge data set.

Looking for faster solution? Here you go!

def find_one_using_hash_map(array)
  map = {}
  dup = nil
  array.each do |v|
    map[v] = (map[v] || 0 ) + 1

    if map[v] > 1
      dup = v

  return dup

It's linear, O(n), but now needs to manage multiple lines-of-code, needs test cases, etc.

If you need an even faster solution, maybe try C instead.

And here is the gist comparing different solutions:

Getting specified Node values from XML document

Just like you do for getting something from the CNode you also need to do for the ANode

XmlNodeList xnList = xml.SelectNodes("/Element[@*]");
foreach (XmlNode xn in xnList)
  XmlNode anode = xn.SelectSingleNode("ANode");
    if (anode!= null)
        string id = anode["ID"].InnerText;
        string date = anode["Date"].InnerText;
        XmlNodeList CNodes = xn.SelectNodes("ANode/BNode/CNode");
        foreach (XmlNode node in CNodes)
         XmlNode example = node.SelectSingleNode("Example");
         if (example != null)
            string na = example["Name"].InnerText;
            string no = example["NO"].InnerText;

SSIS package creating Hresult: 0x80004005 Description: "Login timeout expired" error

The answer here is not clear, so I wanted to add more detail.

Using the link provided above, I performed the following step.

In my XML config manager I changed the "Provider" to SQLOLEDB.1 rather than SQLNCLI.1. This got me past this error.

This information is available at the link the OP posted in the Answer.

The link the got me there:

Vertically center text in a 100% height div?

Since it is absolutely positioned you can use top: 50% to vertically align it in the center.

But then you run into the issue of the page being bigger than you want it to be. For that you can use the overflow: hidden for the parent div. This is what I used to create the same effect:

The CSS:

div.parent {
    width: 100%;
    height: 300px;
    position: relative;
    overflow: hidden;
div.parent div.absolute {
    position: absolute;
    top: 50%;
    height: 300px;


<div class="parent">
    <div class="absolute">This is vertically center aligned</div>

What is a Java String's default initial value?

That depends. Is it just a variable (in a method)? Or a class-member?

If it's just a variable you'll get an error that no value has been set when trying to read from it without first assinging it a value.

If it's a class-member it will be initialized to null by the VM.

psql: FATAL: role "postgres" does not exist

For MAC:

  1. Install Homebrew
  2. brew install postgres
  3. initdb /usr/local/var/postgres
  4. /usr/local/Cellar/postgresql/<version>/bin/createuser -s postgres or /usr/local/opt/postgres/bin/createuser -s postgres which will just use the latest version.
  5. start postgres server manually: pg_ctl -D /usr/local/var/postgres start

To start server at startup

  • mkdir -p ~/Library/LaunchAgents
  • ln -sfv /usr/local/opt/postgresql/*.plist ~/Library/LaunchAgents
  • launchctl load ~/Library/LaunchAgents/homebrew.mxcl.postgresql.plist

Now, it is set up, login using psql -U postgres -h localhost or use PgAdmin for GUI.

By default user postgres will not have any login password.

Check this site for more articles like this:

How to call a function, PostgreSQL

The function call still should be a valid SQL statement:

SELECT "saveUser"(3, 'asd','asd','asd','asd','asd');

number several equations with only one number

How about something like:




    w^T x_i + b \geqslant 1-\xi_i \text{ if } y_i &= 1, \\
    w^T x_i + b \leqslant -1+\xi_i \text{ if } y_i &= -1


which produces:

enter image description here

Single Result from Database by using mySQLi

Use mysqli_fetch_row(). Try this,

$query = "SELECT ssfullname, ssemail FROM userss WHERE user_id = ".$user_id;
$result = mysqli_query($conn, $query);
$row   = mysqli_fetch_row($result);

$ssfullname = $row['ssfullname'];
$ssemail    = $row['ssemail'];

LINQ to SQL Left Outer Join

I found 1 solution. if want to translate this kind of SQL (left join) into Linq Entity...


LEFT OUTER JOIN [REFTABLE] AS [t1] ON ([t0].[trxtype] = [t1].[code])
                                  AND ([t1]. [reftype] = "TRX")


from job in JOBBOOKINGs
join r in (from r1 in REFTABLEs where r1.Reftype=="TRX" select r1) 
          on job.Trxtype equals r.Code into join1
from j in join1.DefaultIfEmpty()
select new

How to make parent wait for all child processes to finish?

pid_t child_pid, wpid;
int status = 0;

//Father code (before child processes start)

for (int id=0; id<n; id++) {
    if ((child_pid = fork()) == 0) {
        //child code

while ((wpid = wait(&status)) > 0); // this way, the father waits for all the child processes 

//Father code (After all child processes end)

wait waits for a child process to terminate, and returns that child process's pid. On error (eg when there are no child processes), -1 is returned. So, basically, the code keeps waiting for child processes to finish, until the waiting errors out, and then you know they are all finished.

Create the perfect JPA entity

My 2 cents addition to the answers here are:

  1. With reference to Field or Property access (away from performance considerations) both are legitimately accessed by means of getters and setters, thus, my model logic can set/get them in the same manner. The difference comes to play when the persistence runtime provider (Hibernate, EclipseLink or else) needs to persist/set some record in Table A which has a foreign key referring to some column in Table B. In case of a Property access type, the persistence runtime system uses my coded setter method to assign the cell in Table B column a new value. In case of a Field access type, the persistence runtime system sets the cell in Table B column directly. This difference is not of importance in the context of a uni-directional relationship, yet it is a MUST to use my own coded setter method (Property access type) for a bi-directional relationship provided the setter method is well designed to account for consistency. Consistency is a critical issue for bi-directional relationships refer to this link for a simple example for a well-designed setter.

  2. With reference to Equals/hashCode: It is impossible to use the Eclipse auto-generated Equals/hashCode methods for entities participating in a bi-directional relationship, otherwise they will have a circular reference resulting in a stackoverflow Exception. Once you try a bidirectional relationship (say OneToOne) and auto-generate Equals() or hashCode() or even toString() you will get caught in this stackoverflow exception.

Change drawable color programmatically

Same as the accepted answer but a simpler convenience method:

val myDrawable = ContextCompat.getDrawable(context, R.drawable.my_drawable)
myDrawable.setColorFilter(Color.GREEN, PorterDuff.Mode.SRC_IN)
setCompoundDrawablesWithIntrinsicBounds(myDrawable, null, null, null)

Note, the code here is Kotlin.

Convert date to YYYYMM format

I know it is an old topic, but If your SQL server version is higher than 2012.

There is another simple option can choose, FORMAT function.

SELECT FORMAT(GetDate(),'yyyyMM')


function declaration isn't a prototype


extern int testlib(void);

Uncaught TypeError: Cannot read property 'value' of undefined

First, you should make sure that document.getElementsByName("username")[0] actually returns an object and not "undefined". You can simply check like

if (typeof document.getElementsByName("username")[0] != 'undefined')

Similarly for the other element password.

Dump Mongo Collection into JSON format

Use mongoexport/mongoimport to dump/restore a collection:

Export JSON File:

mongoexport --db <database-name> --collection <collection-name> --out output.json

Import JSON File:

mongoimport --db <database-name> --collection <collection-name> --file input.json

WARNING mongoimport and mongoexport do not reliably preserve all rich BSON data types because JSON can only represent a subset of the types supported by BSON. As a result, data exported or imported with these tools may lose some measure of fidelity.


BSON is designed to be fast to encode and decode. For example, integers are stored as 32 (or 64) bit integers, so they don't need to be parsed to and from text. This uses more space than JSON for small integers, but is much faster to parse.

In addition to compactness, BSON adds additional data types unavailable in JSON, notably the BinData and Date data types.

Removing duplicate objects with Underscore for Javascript

You can do it in a shorthand as:

_.uniq(foo, 'a')

Traverse a list in reverse order in Python

Also, you could use either "range" or "count" functions. As follows:

a = ["foo", "bar", "baz"]
for i in range(len(a)-1, -1, -1):
    print(i, a[i])

3 baz
2 bar
1 foo

You could also use "count" from itertools as following:

a = ["foo", "bar", "baz"]
from itertools import count, takewhile

def larger_than_0(x):
    return x > 0

for x in takewhile(larger_than_0, count(3, -1)):
    print(x, a[x-1])

3 baz
2 bar
1 foo

Bootstrap 3 with remote Modal

If you don't want to send the full modal structure you can replicate the old behaviour doing something like this:

// this is just an example, remember to adapt the selectors to your code!
$('.modal-link').click(function(e) {
    var modal = $('#modal'), modalBody = $('#modal .modal-body');

        .on('', function () {

The type is defined in an assembly that is not referenced, how to find the cause?

When you get this error it isn't always obvious what is going on, but as the error says - you are missing a reference. Take the following line of code as an example:

MyObjectType a = new MyObjectType("parameter");

It looks simple enough and you probably have referenced "MyObjectType" correctly. But lets say one of the overloads for the "MyObjectType" constructor takes a type that you don't have referenced. For example there is an overload defined as:

public MyObjectType(TypeFromOtherAssembly parameter) {
    // ... normal constructor code ...

That is at least one case where you will get this error. So, look for this type of pattern where you have referenced the type but not all the types of the properties or method parameters that are possible for functions being called on that type.

Hopefully this at least gets you going in the right direction!

How to combine class and ID in CSS selector?

You can combine ID and Class in CSS, but IDs are intended to be unique, so adding a class to a CSS selector would over-qualify it.

Spring not autowiring in unit tests with JUnit

You need to use the Spring JUnit runner in order to wire in Spring beans from your context. The code below assumes that you have a application context called testContest.xml available on the test classpath.

import org.hibernate.SessionFactory;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
import org.springframework.transaction.annotation.Transactional;

import java.sql.SQLException;

import static org.hamcrest.MatcherAssert.assertThat;
import static org.hamcrest.Matchers.startsWith;

@ContextConfiguration(locations = {"classpath*:**/testContext.xml"})
public class someDaoTest {

    protected SessionFactory sessionFactory;

    public void testDBSourceIsCorrect() throws SQLException {
        String databaseProductName = sessionFactory.getCurrentSession()
        assertThat("Test container is pointing at the wrong DB.", databaseProductName, startsWith("HSQL"));

Note: This works with Spring 2.5.2 and Hibernate 3.6.5

What is the 'open' keyword in Swift?

Read open as

open for inheritance in other modules

I repeat open for inheritance in other modules. So an open class is open for subclassing in other modules that include the defining module. Open vars and functions are open for overriding in other modules. Its the least restrictive access level. It is as good as public access except that something that is public is closed for inheritance in other modules.

From Apple Docs:

Open access applies only to classes and class members, and it differs from public access as follows:

  1. Classes with public access, or any more restrictive access level, can be subclassed only within the module where they’re defined.

  2. Class members with public access, or any more restrictive access level, can be overridden by subclasses only within the module where they’re defined.

  3. Open classes can be subclassed within the module where they’re defined, and within any module that imports the module where they’re defined.

  4. Open class members can be overridden by subclasses within the module where they’re defined, and within any module that imports the module where they’re defined.

When to use Hadoop, HBase, Hive and Pig?

First of all we should get clear that Hadoop was created as a faster alternative to RDBMS. To process large amount of data at a very fast rate which earlier took a lot of time in RDBMS.

Now one should know the two terms :

  1. Structured Data : This is the data that we used in traditional RDBMS and is divided into well defined structures.

  2. Unstructured Data : This is important to understand, about 80% of the world data is unstructured or semi structured. These are the data which are on its raw form and cannot be processed using RDMS. Example : facebook, twitter data. (

So, large amount of data was being generated in the last few years and the data was mostly unstructured, that gave birth to HADOOP. It was mainly used for very large amount of data that takes unfeasible amount of time using RDBMS. It had many drawbacks, that it could not be used for comparatively small data in real time but they have managed to remove its drawbacks in the newer version.

Before going further I would like to tell that a new Big Data tool is created when they see a fault on the previous tools. So, whichever tool you will see that is created has been done to overcome the problem of the previous tools.

Hadoop can be simply said as two things : Mapreduce and HDFS. Mapreduce is where the processing takes place and HDFS is the DataBase where data is stored. This structure followed WORM principal i.e. write once read multiple times. So, once we have stored data in HDFS, we cannot make changes. This led to the creation of HBASE, a NOSQL product where we can make changes in the data also after writing it once.

But with time we saw that Hadoop had many faults and for that we created different environment over the Hadoop structure. PIG and HIVE are two popular examples.

HIVE was created for people with SQL background. The queries written is similar to SQL named as HIVEQL. HIVE was developed to process completely structured data. It is not used for ustructured data.

PIG on the other hand has its own query language i.e. PIG LATIN. It can be used for both structured as well as unstructured data.

Moving to the difference as when to use HIVE and when to use PIG, I don't think anyone other than the architect of PIG could say. Follow the link :

What is the instanceof operator in JavaScript?

What is it?

Javascript is a prototypal language which means it uses prototypes for 'inheritance'. the instanceof operator tests if a constructor function's prototype propertype is present in the __proto__ chain of an object. This means that it will do the following (assuming that testObj is a function object):

obj instanceof testObj;
  1. Check if prototype of the object is equal to the prototype of the constructor: obj.__proto__ === testObj.prototype >> if this is true instanceof will return true.
  2. Will climb up the prototype chain. For example: obj.__proto__.__proto__ === testObj.prototype >> if this is true instanceof will return true.
  3. Will repeat step 2 until the full prototype of object is inspected. If nowhere on the prototype chain of the object is matched with testObj.prototype then instanceof operator will return false.


function Person(name) {_x000D_ = name;_x000D_
var me = new Person('Willem');_x000D_
console.log(me instanceof Person); // true_x000D_
// because:  me.__proto__ === Person.prototype  // evaluates true_x000D_
console.log(me instanceof Object); // true_x000D_
// because:  me.__proto__.__proto__ === Object.prototype  // evaluates true_x000D_
console.log(me instanceof Array);  // false_x000D_
// because: Array is nowhere on the prototype chain

What problems does it solve?

It solved the problem of conveniently checking if an object derives from a certain prototype. For example, when a function recieves an object which can have various prototypes. Then, before using methods from the prototype chain, we can use the instanceof operator to check whether the these methods are on the object.


function Person1 (name) {_x000D_ = name;_x000D_
function Person2 (name) {_x000D_ = name;_x000D_
Person1.prototype.talkP1 = function () {_x000D_
  console.log('Person 1 talking');_x000D_
Person2.prototype.talkP2 = function () {_x000D_
  console.log('Person 2 talking');_x000D_
function talk (person) {_x000D_
  if (person instanceof Person1) {_x000D_
  if (person instanceof Person2) {_x000D_
const pers1 = new Person1 ('p1');_x000D_
const pers2 = new Person2 ('p2');_x000D_

Here in the talk() function first is checked if the prototype is located on the object. After this the appropriate method is picked to execute. Not doing this check could result in executing a method which doesn't exist and thus a reference error.

When is it appropriate and when not?

We kind of already went over this. Use it when you are in need of checking the prototype of an object before doing something with it.

How to get index using LINQ?

myCars.Select((v, i) => new {car = v, index = i}).First(myCondition).index;

or the slightly shorter

myCars.Select((car, index) => new {car, index}).First(myCondition).index;

tslint / codelyzer / ng lint error: "for (... in ...) statements must be filtered with an if statement"

To explain the actual problem that tslint is pointing out, a quote from the JavaScript documentation of the statement:

The loop will iterate over all enumerable properties of the object itself and those the object inherits from its constructor's prototype (properties closer to the object in the prototype chain override prototypes' properties).

So, basically this means you'll get properties you might not expect to get (from the object's prototype chain).

To solve this we need to iterate only over the objects own properties. We can do this in two different ways (as suggested by @Maxxx and @Qwertiy).

First solution

for (const field of Object.keys(this.formErrors)) {

Here we utilize the Object.Keys() method which returns an array of a given object's own enumerable properties, in the same order as that provided by a loop (the difference being that a for-in loop enumerates properties in the prototype chain as well).

Second solution

for (var field in this.formErrors) {
    if (this.formErrors.hasOwnProperty(field)) {

In this solution we iterate all of the object's properties including those in it's prototype chain but use the Object.prototype.hasOwnProperty() method, which returns a boolean indicating whether the object has the specified property as own (not inherited) property, to filter the inherited properties out.

Chrome: Uncaught SyntaxError: Unexpected end of input

In cases where your JavaScript code is minified to a single line, another cause for this error is using // instead of /**/ for your comments.

Bad (comments out everything after // including the closing } for your function)

function example() { //comment console.log('TEST'); }

Good (confines your comment)

function example() { /* comment */ console.log('TEST'); }

Reshape an array in NumPy

numpy has a great tool for this task ("numpy.reshape") link to reshape documentation

a = [[ 0  1]
 [ 2  3]
 [ 4  5]
 [ 6  7]
 [ 8  9]
 [10 11]
 [12 13]
 [14 15]
 [16 17]]


you can also use the "-1" trick

`a = a.reshape(-1,3)`

the "-1" is a wild card that will let the numpy algorithm decide on the number to input when the second dimension is 3

so yes.. this would also work: a = a.reshape(3,-1)

and this: a = a.reshape(-1,2) would do nothing

and this: a = a.reshape(-1,9) would change the shape to (2,9)

How can I do width = 100% - 100px in CSS?

Setting the body margins to 0, the width of the outer container to 100%, and using an inner container with 50px left/right margins seems to work.

body {
    margin: 0;
    padding: 0;

    width: 100%;

    margin: 0px 50px 0px 50px;

  <div class="full-width" style="background-color: #ff0000;">
    <div class="innerContainer" style="background-color: #00ff00;">
      content here

What's the difference between .so, .la and .a library files?

.so files are dynamic libraries. The suffix stands for "shared object", because all the applications that are linked with the library use the same file, rather than making a copy in the resulting executable.

.a files are static libraries. The suffix stands for "archive", because they're actually just an archive (made with the ar command -- a predecessor of tar that's now just used for making libraries) of the original .o object files.

.la files are text files used by the GNU "libtools" package to describe the files that make up the corresponding library. You can find more information about them in this question: What are libtool's .la file for?

Static and dynamic libraries each have pros and cons.

Static pro: The user always uses the version of the library that you've tested with your application, so there shouldn't be any surprising compatibility problems.

Static con: If a problem is fixed in a library, you need to redistribute your application to take advantage of it. However, unless it's a library that users are likely to update on their own, you'd might need to do this anyway.

Dynamic pro: Your process's memory footprint is smaller, because the memory used for the library is amortized among all the processes using the library.

Dynamic pro: Libraries can be loaded on demand at run time; this is good for plugins, so you don't have to choose the plugins to be used when compiling and installing the software. New plugins can be added on the fly.

Dynamic con: The library might not exist on the system where someone is trying to install the application, or they might have a version that's not compatible with the application. To mitigate this, the application package might need to include a copy of the library, so it can install it if necessary. This is also often mitigated by package managers, which can download and install any necessary dependencies.

Dynamic con: Link-Time Optimization is generally not possible, so there could possibly be efficiency implications in high-performance applications. See the Wikipedia discussion of WPO and LTO.

Dynamic libraries are especially useful for system libraries, like libc. These libraries often need to include code that's dependent on the specific OS and version, because kernel interfaces have changed. If you link a program with a static system library, it will only run on the version of the OS that this library version was written for. But if you use a dynamic library, it will automatically pick up the library that's installed on the system you run on.

Hibernate Criteria for Dates

try this,

    String dateStr = "17-April-2011 19:20:23.707000000 ";
    Date dateForm = new SimpleDateFormat("dd-MMMM-yyyy HH:mm:ss").parse(dateStr);
    SimpleDateFormat format = new SimpleDateFormat("dd-MM-yyyy");  

    String newDate = format.format(dateForm);  

    Calendar today = Calendar.getInstance();
    Date fromDate = format.parse(newDate);
    today.add(Calendar.DAY_OF_YEAR, 1);
    Date toDate= new SimpleDateFormat("dd-MM-yyyy").parse(format.format(today.getTime()));

    Criteria crit = sessionFactory.getCurrentSession().createCriteria(Model.class);
    crit.add("dateFieldName", fromDate));
    crit.add(Restrictions.le("dateFieldName", toDate));
    return crit.list();

Use URI builder in Android or create URL with variables

Excellent answer from above turned into a simple utility method.

private Uri buildURI(String url, Map<String, String> params) {

    // build url with parameters.
    Uri.Builder builder = Uri.parse(url).buildUpon();
    for (Map.Entry<String, String> entry : params.entrySet()) {
        builder.appendQueryParameter(entry.getKey(), entry.getValue());


How to re-sign the ipa file?

Fastlane's sigh provides a fairly robust solution for resigning IPAs.

From their README:


If you generated your ipa file but want to apply a different code signing onto the ipa file, you can use sigh resign:

fastlane sigh resign

sigh will find the ipa file and the provisioning profile for you if they are located in the current folder.

You can pass more information using the command line:

fastlane sigh resign ./path/app.ipa --signing_identity "iPhone Distribution: Felix Krause" -p "my.mobileprovision"

It will even handle provisioning profiles for nested applications (eg. if you have watchkit apps)

How to Define Callbacks in Android?

to clarify a bit on dragon's answer (since it took me a while to figure out what to do with Handler.Callback):

Handler can be used to execute callbacks in the current or another thread, by passing it Messages. the Message holds data to be used from the callback. a Handler.Callback can be passed to the constructor of Handler in order to avoid extending Handler directly. thus, to execute some code via callback from the current thread:

Message message = new Message();
<set data to be passed to callback - eg message.obj, message.arg1 etc - here>

Callback callback = new Callback() {
    public boolean handleMessage(Message msg) {
        <code to be executed during callback>

Handler handler = new Handler(callback);

EDIT: just realized there's a better way to get the same result (minus control of exactly when to execute the callback):

post(new Runnable() {
    public void run() {
        <code to be executed during callback>

Defining a variable with or without export

Others have answered that export makes the variable available to subshells, and that is correct but merely a side effect. When you export a variable, it puts that variable in the environment of the current shell (ie the shell calls putenv(3) or setenv(3)).
The environment of a process is inherited across exec, making the variable visible in subshells.

Edit (with 5 year's perspective): this is a silly answer. The purpose of 'export' is to make variables "be in the environment of subsequently executed commands", whether those commands be subshells or subprocesses. A naive implementation would be to simply put the variable in the environment of the shell, but this would make it impossible to implement export -p.

How to create a session using JavaScript?

If you create a cookie and do not specify an expiration date, it will create a session cookie which will expire at the end of the session.

See for more information.

enable or disable checkbox in html

If you specify the disabled attribute then the value you give it must be disabled. (In HTML 5 you may leave off everything except the attribute value. In HTML 4 you may leave off everything except the attribute name.)

If you do not want the control to be disabled then do not specify the attribute at all.


<input type="checkbox" disabled>
<input type="checkbox" disabled="disabled">


<input type="checkbox">

Invalid (but usually error recovered to be treated as disabled):

<input type="checkbox" disabled="1">
<input type="checkbox" disabled="true">
<input type="checkbox" disabled="false">

So, without knowing your template language, I guess you are looking for:

<td><input type="checkbox" name="repriseCheckBox" {checkStat == 1 ? disabled : }/></td>

href image link download on click

If you are Using HTML5 you can add the attribute 'download' to your links.

<a href="/test.pdf" download>

How to find an available port?

See ServerSocket:

Creates a server socket, bound to the specified port. A port of 0 creates a socket on any free port.

git reset --hard HEAD leaves untracked files behind

User interactive approach:

git clean -i -fd

Remove .classpath [y/N]? N
Remove .gitignore [y/N]? N
Remove .project [y/N]? N
Remove .settings/ [y/N]? N
Remove src/com/amazon/arsdumpgenerator/inspector/ [y/N]? y
Remove src/com/amazon/arsdumpgenerator/manifest/ [y/N]? y
Remove src/com/amazon/arsdumpgenerator/s3/ [y/N]? y
Remove tst/com/amazon/arsdumpgenerator/manifest/ [y/N]? y
Remove tst/com/amazon/arsdumpgenerator/s3/ [y/N]? y

-i for interactive
-f for force
-d for directory
-x for ignored files(add if required)

Note: Add -n or --dry-run to just check what it will do.

PHP and MySQL Select a Single Value

mysql_* extension has been deprecated in 2013 and removed completely from PHP in 2018. You have two alternatives PDO or MySQLi.


The simpler option is PDO which has a neat helper function fetchColumn():

$stmt = $pdo->prepare("SELECT id FROM Users WHERE username=?");
$stmt->execute([ $_GET["username"] ]);
$value = $stmt->fetchColumn();

Proper PDO tutorial


You can do the same with MySQLi, but it is more complicated:

$stmt = $mysqliConn->prepare('SELECT id FROM Users WHERE username=?');
$stmt->bind_param("s", $_GET["username"]);
$data = $stmt->get_result()->fetch_assoc();
$value = $data ? $data['id'] : null;

fetch_assoc() could return NULL if there are no rows returned from the DB, which is why I check with ternary if there was any data returned.

Run cron job only if it isn't already running

The way I am doing it when I am running php scripts is:

The crontab:

* * * * * php /path/to/php/script.php &

The php code:

if (shell_exec('ps aux | grep ' . __FILE__ . ' | wc  -l') > 1) {
    exit('already running...');
// do stuff

This command is searching in the system process list for the current php filename if it exists the line counter (wc -l) will be greater then one because the search command itself containing the filename

so if you running php crons add the above code to the start of your php code and it will run only once.

What is the easiest way to remove the first character from a string?

Inefficient alternative:


REST API - file (ie images) processing - best practices

There are several decisions to make:

  1. The first about resource path:

    • Model the image as a resource on its own:

      • Nested in user (/user/:id/image): the relationship between the user and the image is made implicitly

      • In the root path (/image):

        • The client is held responsible for establishing the relationship between the image and the user, or;

        • If a security context is being provided with the POST request used to create an image, the server can implicitly establish a relationship between the authenticated user and the image.

    • Embed the image as part of the user

  2. The second decision is about how to represent the image resource:

    • As Base 64 encoded JSON payload
    • As a multipart payload

This would be my decision track:

  • I usually favor design over performance unless there is a strong case for it. It makes the system more maintainable and can be more easily understood by integrators.
  • So my first thought is to go for a Base64 representation of the image resource because it lets you keep everything JSON. If you chose this option you can model the resource path as you like.
    • If the relationship between user and image is 1 to 1 I'd favor to model the image as an attribute specially if both data sets are updated at the same time. In any other case you can freely choose to model the image either as an attribute, updating the it via PUT or PATCH, or as a separate resource.
  • If you choose multipart payload I'd feel compelled to model the image as a resource on is own, so that other resources, in our case, the user resource, is not impacted by the decision of using a binary representation for the image.

Then comes the question: Is there any performance impact about choosing base64 vs multipart?. We could think that exchanging data in multipart format should be more efficient. But this article shows how little do both representations differ in terms of size.

My choice Base64:

  • Consistent design decision
  • Negligible performance impact
  • As browsers understand data URIs (base64 encoded images), there is no need to transform these if the client is a browser
  • I won't cast a vote on whether to have it as an attribute or standalone resource, it depends on your problem domain (which I don't know) and your personal preference.

Visually managing MongoDB documents and collections

There is a web-based project for this that is relatively early on called Pongo. It requires installing Python and some dependencies, but it should run on Windows.

How to implement zoom effect for image view in android?

Here is one of the most efficient way, it works smoothly:

Place in your project. It can then be used the same as ImageView.


TouchImageView img = (TouchImageView) findViewById(;

If you are using TouchImageView in xml, then you must provide the full package name, because it is a custom view.


            android:layout_height="match_parent" />

installing apache: no VCRUNTIME140.dll

I had same problem, my issue was that downloaded Apache 2.4 but 32 bits. Then re-download 64bits version and it's works.

I hope it helps you

Comparing two vectors in an if statement

Are they identical?

> identical(A,C)

Which elements disagree:

> which(A != C)
[1] 2 4

Detect viewport orientation, if orientation is Portrait display alert message advising user of instructions

I used for Android Chrome "The Screen Orientation API"

To look the current orientation call console.log(screen.orientation.type) (and maybe screen.orientation.angle).

Results: portrait-primary | portrait-secondary | landscape-primary | landscape-secondary

Below is my code, I hope it'll be helpful:

var m_isOrientation = ("orientation" in screen) && (typeof screen.orientation.lock == 'function') && (typeof screen.orientation.unlock == 'function');
if (!isFullscreen()) return;
    function() {
        console.log('new orientation is landscape-secondary');
    function(e) {
);//here's Promise
  • I tested only for Android Chrome - ok

How to change the Jupyter start-up folder

For Windows 10:

  1. Look for Jupiter notebook shortcut (in Start menu>Anaconda).
  2. Right click and Properties.
  3. Add the path that you would like (but use / not \ for path) as showed on the screenshot:

enter image description here

Java JDBC connection status

Your best chance is to just perform a simple query against one table, e.g.:

select 1 from SOME_TABLE;

Oh, I just saw there is a new method available since 1.6:

java.sql.Connection.isValid(int timeoutSeconds):

Returns true if the connection has not been closed and is still valid. The driver shall submit a query on the connection or use some other mechanism that positively verifies the connection is still valid when this method is called. The query submitted by the driver to validate the connection shall be executed in the context of the current transaction.

Writing JSON object to a JSON file with fs.writeFileSync

to open a local file or url with chrome, i used:

const open = require('open'); // npm i open
// open('')
open('build_mytest/index.html', {app: "chrome.exe"})

How can I disable editing cells in a WPF Datagrid?

The DataGrid has an XAML property IsReadOnly that you can set to true:


Hide vertical scrollbar in <select> element

Chrome (and maybe other webkit browsers) only:

/* you probably want to specify the size if you're going to disable the scrollbar */_x000D_
select[size]::-webkit-scrollbar {_x000D_
 display: none;_x000D_
<select size=4>_x000D_

DropdownList DataSource

Refer to example at this link. It may be help to you.

void Page_Load(Object sender, EventArgs e)

     // Load data for the DropDownList control only once, when the 
     // page is first loaded.

        // Specify the data source and field names for the Text 
        // and Value properties of the items (ListItem objects) 
        // in the DropDownList control.
        ColorList.DataSource = CreateDataSource();
        ColorList.DataTextField = "ColorTextField";
        ColorList.DataValueField = "ColorValueField";

        // Bind the data to the control.

        // Set the default selected item, if desired.
        ColorList.SelectedIndex = 0;



void Selection_Change(Object sender, EventArgs e)

     // Set the background color for days in the Calendar control
     // based on the value selected by the user from the 
     // DropDownList control.
     Calendar1.DayStyle.BackColor = 


Node.js - SyntaxError: Unexpected token import

I'm shocked esm hasn't been mentioned. This small, but mighty package allows you to use either import or require.

Install esm in your project

$ npm install --save esm

Update your Node Start Script to use esm

node -r esm app.js

esm just works. I wasted a TON of time with .mjs and --experimental-modules only to find out a .mjs file cannot import a file that uses require or module.exports. This was a huge problem, whereas esm allows you to mix and match and it just figures it out... esm just works.

jQuery ajax post file field

I tried this code to accept files using Ajax and on submit file gets store using my php file. Code modified slightly to work. (Uploaded Files: PDF,JPG)

function verify1() {
        type: 'POST',
        data: new FormData($("#infoForm1")[0]),
        processData: false, 
        contentType: false, 
        success: function(returnval) {

Just print the file details and check. You will get Output. If error let me know.

Remove characters from C# string

Here is a nice way to remove the invalid characters in a Filename:

string.Join(string.Empty, filename.Split(System.IO.Path.GetInvalidFileNameChars()));

Passing a 2D array to a C++ function

We can use several ways to pass a 2D array to a function:

  • Using single pointer we have to typecast the 2D array.

     using namespace std;
     void func(int *arr, int m, int n)
         for (int i=0; i<m; i++)
            for (int j=0; j<n; j++)
               cout<<*((arr+i*n) + j)<<" ";
     int main()
         int m = 3, n = 3;
         int arr[m][n] = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};
         func((int *)arr, m, n);
         return 0;
  • Using double pointer In this way, we also typecast the 2d array

     using namespace std;
    void func(int **arr, int row, int col)
       for (int i=0; i<row; i++)
          for(int j=0 ; j<col; j++)
            cout<<arr[i][j]<<" ";
    int main()
      int row, colum;
      int** arr = new int*[row];
      for(int i=0; i<row; i++)
         arr[i] = new int[colum];
      for(int i=0; i<row; i++)
          for(int j=0; j<colum; j++)
      func(arr, row, colum);
      return 0;

How to programmatically take a screenshot on Android?

Here is the code that allowed my screenshot to be stored on an SD card and used later for whatever your needs are:

First, you need to add a proper permission to save the file:

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

And this is the code (running in an Activity):

private void takeScreenshot() {
    Date now = new Date();
    android.text.format.DateFormat.format("yyyy-MM-dd_hh:mm:ss", now);

    try {
        // image naming and path  to include sd card  appending name you choose for file
        String mPath = Environment.getExternalStorageDirectory().toString() + "/" + now + ".jpg";

        // create bitmap screen capture
        View v1 = getWindow().getDecorView().getRootView();
        Bitmap bitmap = Bitmap.createBitmap(v1.getDrawingCache());

        File imageFile = new File(mPath);

        FileOutputStream outputStream = new FileOutputStream(imageFile);
        int quality = 100;
        bitmap.compress(Bitmap.CompressFormat.JPEG, quality, outputStream);

    } catch (Throwable e) {
        // Several error may come out with file handling or DOM

And this is how you can open the recently generated image:

private void openScreenshot(File imageFile) {
    Intent intent = new Intent();
    Uri uri = Uri.fromFile(imageFile);
    intent.setDataAndType(uri, "image/*");

If you want to use this on fragment view then use:

View v1 = getActivity().getWindow().getDecorView().getRootView();

instead of

View v1 = getWindow().getDecorView().getRootView();

on takeScreenshot() function


This solution doesn't work if your dialog contains a surface view. For details please check the answer to the following question:

Android Take Screenshot of Surface View Shows Black Screen

Test or check if sheet exists

I know it is an old post, but here is another simple solution that is fast.

Public Function worksheetExists(ByVal wb As Workbook, ByVal sheetNameStr As String) As Boolean

On Error Resume Next
worksheetExists = (wb.Worksheets(sheetNameStr).Name <> "")
Err.Clear: On Error GoTo 0

End Function

Jquery to change form action

Try this:

   $('#formId').attr('action', 'page1');

   $('#formId').attr('action', 'page2');

What is the best way to connect and use a sqlite database from C#

I've used this with great success:

Free with no restrictions.

(Note from review: Original site no longer exists. The above link has a link pointing the the 404 site and has all the info of the original)


How to make program go back to the top of the code instead of closing

You need to use a while loop. If you make a while loop, and there's no instruction after the loop, it'll become an infinite loop,and won't stop until you manually stop it.

Taking multiple inputs from user in python

You can try this.

import sys

for line in sys.stdin:
    j= int(line[0])
    e= float(line[1])
    t= str(line[2])

For details, please review,

Can media queries resize based on a div element instead of the screen?

A Media Query inside of an iframe can function as an element query. I've successfully implement this. The idea came from a recent post about Responsive Ads by Zurb. No Javascript!

What does the function then() mean in JavaScript?

.then returns a promise in async function.

Good Example would be:

var doSome = new Promise(function(resolve, reject){
    resolve('I am doing something');


To add another logic to it, you can also add the reject('I am the rejected param') call the function and console.log it.

Flask example with POST

Here is the example in which you can easily find the way to use Post,GET method and use the same way to add other curd operations as well..

#libraries to include

import os
from flask import request, jsonify
from app import app, mongo
import logger
ROOT_PATH = os.environ.get('ROOT_PATH')<br>
@app.route('/get/questions/', methods=['GET', 'POST','DELETE', 'PATCH'])
    def question():
    # request.args is to get urls arguments 

    if request.method == 'GET':
        start = request.args.get('start', default=0, type=int)
        limit_url = request.args.get('limit', default=20, type=int)
        questions = mongo.db.questions.find().limit(limit_url).skip(start);
        data = [doc for doc in questions]
        return jsonify(isError= False,
                    message= "Success",
                    statusCode= 200,
                    data= data), 200

# request.form to get form parameter

    if request.method == 'POST':
        average_time = request.form.get('average_time')
        choices = request.form.get('choices')
        created_by = request.form.get('created_by')
        difficulty_level = request.form.get('difficulty_level')
        question = request.form.get('question')
        topics = request.form.get('topics')

    ##Do something like insert in DB or Render somewhere etc. it's up to you....... :)

Multiple parameters in a List. How to create without a class?

List only accepts one type parameter. The closest you'll get with List is:

 var list = new List<Tuple<string, int>>();
 list.Add(Tuple.Create("hello", 1));

Could not find main class HelloWorld

I have also faced same problem....

Actually this problem is raised due to the fact that your program .class files are not saved in that directory. Remove your CLASSPATH from your environment variable (you do no need to set classpath for simple Java programs) and reopen cmd prompt, then compile and execute.

If you observe carefully your .class file will save in the same location. (I am not an expert, I am also basic programer if there is any mistake in my sentences please ignore it :-))

How to set custom favicon in Express?

No extra middlewares required. Just use:

app.use('/favicon.ico', express.static('images/favicon.ico'));

Asynchronous shell exec in PHP

In Linux, you can start a process in a new independent thread by appending an ampersand at the end of the command

mycommand -someparam somevalue &

In Windows, you can use the "start" DOS command

start mycommand -someparam somevalue

What is the memory consumption of an object in Java?

No, registering an object takes a bit of memory too. 100 objects with 1 attribute will take up more memory.

How to check compiler log in sql developer?

To see your log in SQL Developer then press:

CTRL+SHIFT + L (or CTRL + CMD + L on macOS)


View -> Log

or by using mysql query

show errors;

Is there a 'foreach' function in Python 3?

map can be used for the situation mentioned in the question.


map(len, ['abcd','abc', 'a']) # 4 3 1

For functions that take multiple arguments, more arguments can be given to map:

map(pow, [2, 3], [4,2]) # 16 9

It returns a list in python 2.x and an iterator in python 3

In case your function takes multiple arguments and the arguments are already in the form of tuples (or any iterable since python 2.6) you can use itertools.starmap. (which has a very similar syntax to what you were looking for). It returns an iterator.


for num in starmap(pow, [(2,3), (3,2)]):

gives us 8 and 9

Get time of specific timezone

You could use Intl.DateTimeFormat.

let options = {_x000D_
    timeZone: 'Europe/London',_x000D_
    year: 'numeric',_x000D_
    month: 'numeric',_x000D_
    day: 'numeric',_x000D_
    hour: 'numeric',_x000D_
    minute: 'numeric',_x000D_
    second: 'numeric',_x000D_
  formatter = new Intl.DateTimeFormat([], options);_x000D_
console.log(formatter.format(new Date()));

Alternatively, if you're formatting just once instead of bulk use Date.prototype.toLocaleDateString().

(new Date()).toLocaleString([], options)

Unfortunately browsers are not required to understand timezones other than UTC, so try these blocks and figure out an alternative in case it fails, for example fetch the timezone offset from a server.

Get installed applications in a system

The object for the list:

public class InstalledProgram
    public string DisplayName { get; set; }
    public string Version { get; set; }
    public string InstalledDate { get; set; }
    public string Publisher { get; set; }
    public string UnninstallCommand { get; set; }
    public string ModifyPath { get; set; }

The call for creating the list:

    List<InstalledProgram> installedprograms = new List<InstalledProgram>();
    string registry_key = @"SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall";
    using (RegistryKey key = Registry.LocalMachine.OpenSubKey(registry_key))
        foreach (string subkey_name in key.GetSubKeyNames())
            using (RegistryKey subkey = key.OpenSubKey(subkey_name))
                if (subkey.GetValue("DisplayName") != null)
                    installedprograms.Add(new InstalledProgram
                        DisplayName = (string)subkey.GetValue("DisplayName"),
                        Version = (string)subkey.GetValue("DisplayVersion"),
                        InstalledDate = (string)subkey.GetValue("InstallDate"),
                        Publisher = (string)subkey.GetValue("Publisher"),
                        UnninstallCommand = (string)subkey.GetValue("UninstallString"),
                        ModifyPath = (string)subkey.GetValue("ModifyPath")

Reference alias (calculated in SELECT) in WHERE clause

It's actually possible to effectively define a variable that can be used in both the SELECT, WHERE and other clauses.

A cross join doesn't necessarily allow for appropriate binding to the referenced table columns, however OUTER APPLY does - and treats nulls more transparently.

    Entity e
        -- variables   
        BalanceDue = e.EntityTypeId,
        Variable2 = ...some..long..complex..expression..etc...
    ) vars
    vars.BalanceDue > 0

Kudos to Syed Mehroz Alam.

Difference between float and decimal data type

MySQL recently changed they way they store the DECIMAL type. In the past they stored the characters (or nybbles) for each digit comprising an ASCII (or nybble) representation of a number - vs - a two's complement integer, or some derivative thereof.

The current storage format for DECIMAL is a series of 1,2,3,or 4-byte integers whose bits are concatenated to create a two's complement number with an implied decimal point, defined by you, and stored in the DB schema when you declare the column and specify it's DECIMAL size and decimal point position.

By way of example, if you take a 32-bit int you can store any number from 0 - 4,294,967,295. That will only reliably cover 999,999,999, so if you threw out 2 bits and used (1<<30 -1) you'd give up nothing. Covering all 9-digit numbers with only 4 bytes is more efficient than covering 4 digits in 32 bits using 4 ASCII characters, or 8 nybble digits. (a nybble is 4-bits, allowing values 0-15, more than is needed for 0-9, but you can't eliminate that waste by going to 3 bits, because that only covers values 0-7)

The example used on the MySQL online docs uses DECIMAL(18,9) as an example. This is 9 digits ahead of and 9 digits behind the implied decimal point, which as explained above requires the following storage.

As 18 8-bit chars: 144 bits

As 18 4-bit nybbles: 72 bits

As 2 32-bit integers: 64 bits

Currently DECIMAL supports a max of 65 digits, as DECIMAL(M,D) where the largest value for M allowed is 65, and the largest value of D allowed is 30.

So as not to require chunks of 9 digits at a time, integers smaller than 32-bits are used to add digits using 1,2 and 3 byte integers. For some reason that defies logic, signed, instead of unsigned ints were used, and in so doing, 1 bit gets thrown out, resulting in the following storage capabilities. For 1,2 and 4 byte ints the lost bit doesn't matter, but for the 3-byte int it's a disaster because an entire digit is lost due to the loss of that single bit.

With an 7-bit int: 0 - 99

With a 15-bit int: 0 - 9,999

With a 23-bit int: 0 - 999,999 (0 - 9,999,999 with a 24-bit int)

1,2,3 and 4-byte integers are concatenated together to form a "bit pool" DECIMAL uses to represent the number precisely as a two's complement integer. The decimal point is NOT stored, it is implied.

This means that no ASCII to int conversions are required of the DB engine to convert the "number" into something the CPU recognizes as a number. No rounding, no conversion errors, it's a real number the CPU can manipulate.

Calculations on this arbitrarily large integer must be done in software, as there is no hardware support for this kind of number, but these libraries are very old and highly optimized, having been written 50 years ago to support IBM 370 Fortran arbitrary precision floating point data. They're still a lot slower than fixed-sized integer algebra done with CPU integer hardware, or floating point calculations done on the FPU.

In terms of storage efficiency, because the exponent of a float is attached to each and every float, specifying implicitly where the decimal point is, it is massively redundant, and therefore inefficient for DB work. In a DB you already know where the decimal point is to go up front, and every row in the table that has a value for a DECIMAL column need only look at the 1 & only specification of where that decimal point is to be placed, stored in the schema as the arguments to a DECIMAL(M,D) as the implication of the M and the D values.

The many remarks found here about which format is to be used for various kinds of applications are correct, so I won't belabor the point. I took the time to write this here because whoever is maintaining the linked MySQL online documentation doesn't understand any of the above and after rounds of increasingly frustrating attempts to explain it to them I gave up. A good indication of how poorly they understood what they were writing is the very muddled and almost indecipherable presentation of the subject matter.

As a final thought, if you have need of high-precision floating point computation, there've been tremendous advances in floating point code in the last 20 years, and hardware support for 96-bit and Quadruple Precision float are right around the corner, but there are good arbitrary precision libraries out there if manipulation of the stored value is important.

How to calculate 1st and 3rd quartiles?

In my efforts to learn object-oriented programming alongside learning statistics, I made this, maybe you'll find it useful:

samplesCourse = [9, 10, 10, 11, 13, 15, 16, 19, 19, 21, 23, 28, 30, 33, 34, 36, 44, 45, 47, 60]

class sampleSet:
    def __init__(self, sampleList):
        self.sampleList = sampleList
        self.interList = list(sampleList) # interList is sampleList alias; alias used to maintain integrity of original sampleList

    def find_median(self):
        self.median = 0

        if len(self.sampleList) % 2 == 0:
            # find median for even-numbered sample list length
            self.medL = self.interList[int(len(self.interList)/2)-1]
            self.medU = self.interList[int(len(self.interList)/2)]
            self.median = (self.medL + self.medU)/2

            # find median for odd-numbered sample list length
            self.median = self.interList[int((len(self.interList)-1)/2)]
        return self.median

    def find_1stQuartile(self, median):
        self.lower50List = []
        self.Q1 = 0

        # break out lower 50 percentile from sampleList
        if len(self.interList) % 2 == 0:
            self.lower50List = self.interList[:int(len(self.interList)/2)]
            # drop median to make list ready to divide into 50 percentiles
            self.lower50List = self.interList[:int(len(self.interList)/2)]

        # find 1st quartile (median of lower 50 percentiles)
        if len(self.lower50List) % 2 == 0:
            self.Q1L = self.lower50List[int(len(self.lower50List)/2)-1]
            self.Q1U = self.lower50List[int(len(self.lower50List)/2)]
            self.Q1 = (self.Q1L + self.Q1U)/2

            self.Q1 = self.lower50List[int((len(self.lower50List)-1)/2)]

        return self.Q1

    def find_3rdQuartile(self, median):
        self.upper50List = []
        self.Q3 = 0

        # break out upper 50 percentile from sampleList
        if len(self.sampleList) % 2 == 0:
            self.upper50List = self.interList[int(len(self.interList)/2):]
            self.upper50List = self.interList[int(len(self.interList)/2):]

        # find 3rd quartile (median of upper 50 percentiles)
        if len(self.upper50List) % 2 == 0:
            self.Q3L = self.upper50List[int(len(self.upper50List)/2)-1]
            self.Q3U = self.upper50List[int(len(self.upper50List)/2)]
            self.Q3 = (self.Q3L + self.Q3U)/2

            self.Q3 = self.upper50List[int((len(self.upper50List)-1)/2)]

        return self.Q3

    def find_InterQuartileRange(self, Q1, Q3):
        self.IQR = self.Q3 - self.Q1
        return self.IQR

    def find_UpperFence(self, Q3, IQR):
        self.fence = self.Q3 + 1.5 * self.IQR
        return self.fence

samples = sampleSet(samplesCourse)
median = samples.find_median()
firstQ = samples.find_1stQuartile(median)
thirdQ = samples.find_3rdQuartile(median)
iqr = samples.find_InterQuartileRange(firstQ, thirdQ)
fence = samples.find_UpperFence(thirdQ, iqr)

print("Median is: ", median)
print("1st quartile is: ", firstQ)
print("3rd quartile is: ", thirdQ)
print("IQR is: ", iqr)
print("Upper fence is: ", fence)

image processing to improve tesseract OCR accuracy

Text Recognition depends on a variety of factors to produce a good quality output. OCR output highly depends on the quality of input image. This is why every OCR engine provides guidelines regarding the quality of input image and its size. These guidelines help OCR engine to produce accurate results.

I have written a detailed article on image processing in python. Kindly follow the link below for more explanation. Also added the python source code to implement those process.

Please write a comment if you have a suggestion or better idea on this topic to improve it.

Running Bash commands in Python

To somewhat expand on the earlier answers here, there are a number of details which are commonly overlooked.

  • Prefer over subprocess.check_call() and friends over over subprocess.Popen() over os.system() over os.popen()
  • Understand and probably use text=True, aka universal_newlines=True.
  • Understand the meaning of shell=True or shell=False and how it changes quoting and the availability of shell conveniences.
  • Understand differences between sh and Bash
  • Understand how a subprocess is separate from its parent, and generally cannot change the parent.
  • Avoid running the Python interpreter as a subprocess of Python.

These topics are covered in some more detail below.

Prefer or subprocess.check_call()

The subprocess.Popen() function is a low-level workhorse but it is tricky to use correctly and you end up copy/pasting multiple lines of code ... which conveniently already exist in the standard library as a set of higher-level wrapper functions for various purposes, which are presented in more detail in the following.

Here's a paragraph from the documentation:

The recommended approach to invoking subprocesses is to use the run() function for all use cases it can handle. For more advanced use cases, the underlying Popen interface can be used directly.

Unfortunately, the availability of these wrapper functions differs between Python versions.

  • was officially introduced in Python 3.5. It is meant to replace all of the following.
  • subprocess.check_output() was introduced in Python 2.7 / 3.1. It is basically equivalent to, check=True, stdout=subprocess.PIPE).stdout
  • subprocess.check_call() was introduced in Python 2.5. It is basically equivalent to, check=True)
  • was introduced in Python 2.4 in the original subprocess module (PEP-324). It is basically equivalent to

High-level API vs subprocess.Popen()

The refactored and extended is more logical and more versatile than the older legacy functions it replaces. It returns a CompletedProcess object which has various methods which allow you to retrieve the exit status, the standard output, and a few other results and status indicators from the finished subprocess. is the way to go if you simply need a program to run and return control to Python. For more involved scenarios (background processes, perhaps with interactive I/O with the Python parent program) you still need to use subprocess.Popen() and take care of all the plumbing yourself. This requires a fairly intricate understanding of all the moving parts and should not be undertaken lightly. The simpler Popen object represents the (possibly still-running) process which needs to be managed from your code for the remainder of the lifetime of the subprocess.

It should perhaps be emphasized that just subprocess.Popen() merely creates a process. If you leave it at that, you have a subprocess running concurrently alongside with Python, so a "background" process. If it doesn't need to do input or output or otherwise coordinate with you, it can do useful work in parallel with your Python program.

Avoid os.system() and os.popen()

Since time eternal (well, since Python 2.5) the os module documentation has contained the recommendation to prefer subprocess over os.system():

The subprocess module provides more powerful facilities for spawning new processes and retrieving their results; using that module is preferable to using this function.

The problems with system() are that it's obviously system-dependent and doesn't offer ways to interact with the subprocess. It simply runs, with standard output and standard error outside of Python's reach. The only information Python receives back is the exit status of the command (zero means success, though the meaning of non-zero values is also somewhat system-dependent).

PEP-324 (which was already mentioned above) contains a more detailed rationale for why os.system is problematic and how subprocess attempts to solve those issues.

os.popen() used to be even more strongly discouraged:

Deprecated since version 2.6: This function is obsolete. Use the subprocess module.

However, since sometime in Python 3, it has been reimplemented to simply use subprocess, and redirects to the subprocess.Popen() documentation for details.

Understand and usually use check=True

You'll also notice that has many of the same limitations as os.system(). In regular use, you should generally check whether the process finished successfully, which subprocess.check_call() and subprocess.check_output() do (where the latter also returns the standard output of the finished subprocess). Similarly, you should usually use check=True with unless you specifically need to allow the subprocess to return an error status.

In practice, with check=True or subprocess.check_*, Python will throw a CalledProcessError exception if the subprocess returns a nonzero exit status.

A common error with is to omit check=True and be surprised when downstream code fails if the subprocess failed.

On the other hand, a common problem with check_call() and check_output() was that users who blindly used these functions were surprised when the exception was raised e.g. when grep did not find a match. (You should probably replace grep with native Python code anyway, as outlined below.)

All things counted, you need to understand how shell commands return an exit code, and under what conditions they will return a non-zero (error) exit code, and make a conscious decision how exactly it should be handled.

Understand and probably use text=True aka universal_newlines=True

Since Python 3, strings internal to Python are Unicode strings. But there is no guarantee that a subprocess generates Unicode output, or strings at all.

(If the differences are not immediately obvious, Ned Batchelder's Pragmatic Unicode is recommended, if not outright obligatory, reading. There is a 36-minute video presentation behind the link if you prefer, though reading the page yourself will probably take significantly less time.)

Deep down, Python has to fetch a bytes buffer and interpret it somehow. If it contains a blob of binary data, it shouldn't be decoded into a Unicode string, because that's error-prone and bug-inducing behavior - precisely the sort of pesky behavior which riddled many Python 2 scripts, before there was a way to properly distinguish between encoded text and binary data.

With text=True, you tell Python that you, in fact, expect back textual data in the system's default encoding, and that it should be decoded into a Python (Unicode) string to the best of Python's ability (usually UTF-8 on any moderately up to date system, except perhaps Windows?)

If that's not what you request back, Python will just give you bytes strings in the stdout and stderr strings. Maybe at some later point you do know that they were text strings after all, and you know their encoding. Then, you can decode them.

normal =[external, arg],
    stdout=subprocess.PIPE, stderr=subprocess.PIPE,

convoluted =[external, arg],
    stdout=subprocess.PIPE, stderr=subprocess.PIPE,
# You have to know (or guess) the encoding

Python 3.7 introduced the shorter and more descriptive and understandable alias text for the keyword argument which was previously somewhat misleadingly called universal_newlines.

Understand shell=True vs shell=False

With shell=True you pass a single string to your shell, and the shell takes it from there.

With shell=False you pass a list of arguments to the OS, bypassing the shell.

When you don't have a shell, you save a process and get rid of a fairly substantial amount of hidden complexity, which may or may not harbor bugs or even security problems.

On the other hand, when you don't have a shell, you don't have redirection, wildcard expansion, job control, and a large number of other shell features.

A common mistake is to use shell=True and then still pass Python a list of tokens, or vice versa. This happens to work in some cases, but is really ill-defined and could break in interesting ways.

buggy ='dig +short')

broken =['dig', '+short', ''],

pathological =['dig +short'],

correct =['dig', '+short', ''],
    # Probably don't forget these, too
    check=True, text=True)

# XXX Probably better avoid shell=True
# but this is nominally correct
fixed_but_fugly ='dig +short',
    # Probably don't forget these, too
    check=True, text=True)

The common retort "but it works for me" is not a useful rebuttal unless you understand exactly under what circumstances it could stop working.

Refactoring Example

Very often, the features of the shell can be replaced with native Python code. Simple Awk or sed scripts should probably simply be translated to Python instead.

To partially illustrate this, here is a typical but slightly silly example which involves many shell features.

cmd = '''while read -r x;
   do ping -c 3 "$x" | grep 'round-trip min/avg/max'
   done <hosts.txt'''

# Trivial but horrible
results =
    cmd, shell=True, universal_newlines=True, check=True)

# Reimplement with shell=False
with open('hosts.txt') as hosts:
    for host in hosts:
        host = host.rstrip('\n')  # drop newline
        ping =
             ['ping', '-c', '3', host],
        for line in ping.stdout.split('\n'):
             if 'round-trip min/avg/max' in line:
                 print('{}: {}'.format(host, line))

Some things to note here:

  • With shell=False you don't need the quoting that the shell requires around strings. Putting quotes anyway is probably an error.
  • It often makes sense to run as little code as possible in a subprocess. This gives you more control over execution from within your Python code.
  • Having said that, complex shell pipelines are tedious and sometimes challenging to reimplement in Python.

The refactored code also illustrates just how much the shell really does for you with a very terse syntax -- for better or for worse. Python says explicit is better than implicit but the Python code is rather verbose and arguably looks more complex than this really is. On the other hand, it offers a number of points where you can grab control in the middle of something else, as trivially exemplified by the enhancement that we can easily include the host name along with the shell command output. (This is by no means challenging to do in the shell, either, but at the expense of yet another diversion and perhaps another process.)

Common Shell Constructs

For completeness, here are brief explanations of some of these shell features, and some notes on how they can perhaps be replaced with native Python facilities.

  • Globbing aka wildcard expansion can be replaced with glob.glob() or very often with simple Python string comparisons like for file in os.listdir('.'): if not file.endswith('.png'): continue. Bash has various other expansion facilities like .{png,jpg} brace expansion and {1..100} as well as tilde expansion (~ expands to your home directory, and more generally ~account to the home directory of another user)
  • Shell variables like $SHELL or $my_exported_var can sometimes simply be replaced with Python variables. Exported shell variables are available as e.g. os.environ['SHELL'] (the meaning of export is to make the variable available to subprocesses -- a variable which is not available to subprocesses will obviously not be available to Python running as a subprocess of the shell, or vice versa. The env= keyword argument to subprocess methods allows you to define the environment of the subprocess as a dictionary, so that's one way to make a Python variable visible to a subprocess). With shell=False you will need to understand how to remove any quotes; for example, cd "$HOME" is equivalent to os.chdir(os.environ['HOME']) without quotes around the directory name. (Very often cd is not useful or necessary anyway, and many beginners omit the double quotes around the variable and get away with it until one day ...)
  • Redirection allows you to read from a file as your standard input, and write your standard output to a file. grep 'foo' <inputfile >outputfile opens outputfile for writing and inputfile for reading, and passes its contents as standard input to grep, whose standard output then lands in outputfile. This is not generally hard to replace with native Python code.
  • Pipelines are a form of redirection. echo foo | nl runs two subprocesses, where the standard output of echo is the standard input of nl (on the OS level, in Unix-like systems, this is a single file handle). If you cannot replace one or both ends of the pipeline with native Python code, perhaps think about using a shell after all, especially if the pipeline has more than two or three processes (though look at the pipes module in the Python standard library or a number of more modern and versatile third-party competitors).
  • Job control lets you interrupt jobs, run them in the background, return them to the foreground, etc. The basic Unix signals to stop and continue a process are of course available from Python, too. But jobs are a higher-level abstraction in the shell which involve process groups etc which you have to understand if you want to do something like this from Python.
  • Quoting in the shell is potentially confusing until you understand that everything is basically a string. So ls -l / is equivalent to 'ls' '-l' '/' but the quoting around literals is completely optional. Unquoted strings which contain shell metacharacters undergo parameter expansion, whitespace tokenization and wildcard expansion; double quotes prevent whitespace tokenization and wildcard expansion but allow parameter expansions (variable substitution, command substitution, and backslash processing). This is simple in theory but can get bewildering, especially when there are several layers of interpretation (a remote shell command, for example).

Understand differences between sh and Bash

subprocess runs your shell commands with /bin/sh unless you specifically request otherwise (except of course on Windows, where it uses the value of the COMSPEC variable). This means that various Bash-only features like arrays, [[ etc are not available.

If you need to use Bash-only syntax, you can pass in the path to the shell as executable='/bin/bash' (where of course if your Bash is installed somewhere else, you need to adjust the path).'''
    # This for loop syntax is Bash only
    for((i=1;i<=$#;i++)); do
        # Arrays are Bash-only
    shell=True, check=True,

A subprocess is separate from its parent, and cannot change it

A somewhat common mistake is doing something like'cd /tmp', shell=True)'pwd', shell=True)  # Oops, doesn't print /tmp

The same thing will happen if the first subprocess tries to set an environment variable, which of course will have disappeared when you run another subprocess, etc.

A child process runs completely separate from Python, and when it finishes, Python has no idea what it did (apart from the vague indicators that it can infer from the exit status and output from the child process). A child generally cannot change the parent's environment; it cannot set a variable, change the working directory, or, in so many words, communicate with its parent without cooperation from the parent.

The immediate fix in this particular case is to run both commands in a single subprocess;'cd /tmp; pwd', shell=True)

though obviously this particular use case isn't very useful; instead, use the cwd keyword argument, or simply os.chdir() before running the subprocess. Similarly, for setting a variable, you can manipulate the environment of the current process (and thus also its children) via

os.environ['foo'] = 'bar'

or pass an environment setting to a child process with'echo "$foo"', shell=True, env={'foo': 'bar'})

(not to mention the obvious refactoring['echo', 'bar']); but echo is a poor example of something to run in a subprocess in the first place, of course).

Don't run Python from Python

This is slightly dubious advice; there are certainly situations where it does make sense or is even an absolute requirement to run the Python interpreter as a subprocess from a Python script. But very frequently, the correct approach is simply to import the other Python module into your calling script and call its functions directly.

If the other Python script is under your control, and it isn't a module, consider turning it into one. (This answer is too long already so I will not delve into details here.)

If you need parallelism, you can run Python functions in subprocesses with the multiprocessing module. There is also threading which runs multiple tasks in a single process (which is more lightweight and gives you more control, but also more constrained in that threads within a process are tightly coupled, and bound to a single GIL.)

Add column with constant value to pandas dataframe

Here is another one liner using lambdas (create column with constant value = 10)

df['newCol'] = df.apply(lambda x: 10, axis=1)


    A           B           C
1   1.764052    0.400157    0.978738
2   2.240893    1.867558    -0.977278
3   0.950088    -0.151357   -0.103219


        A           B           C           newCol
    1   1.764052    0.400157    0.978738    10
    2   2.240893    1.867558    -0.977278   10
    3   0.950088    -0.151357   -0.103219   10

SQL Query to find missing rows between two related tables






Please note that these queries do not require that ABC_ID be in table B at all. I think that does what you want.

How to pass the -D System properties while testing on Eclipse?

Yes this is the way:

Right click on your program, select run -> run configuration then on vm argument

-Denv=EnvironmentName -Dcucumber.options="--tags @ifThereisAnyTag"

Then you can apply and close.

Restoring database from .mdf and .ldf files of SQL Server 2008

this is what i did

first execute create database x. x is the name of your old database eg the name of the mdf.

Then open sql sever configration and stop the sql sever.

There after browse to the location of your new created database it should be under program file, in my case is

C:\Program Files\Microsoft SQL Server\MSSQL14.MSSQL\MSSQL\DATA

and repleace the new created mdf and Idf with the old files/database.

then simply restart the sql server and walla :)

"NOT IN" clause in LINQ to Entities


from p in db.Products
where !theBadCategories.Contains(p.Category)
select p;

What's the SQL query you want to translate into a Linq query?

In Rails, how do you render JSON using a view?

Try adding a view users/show.json.erb This should be rendered when you make a request for the JSON format, and you get the added benefit of it being rendered by erb too, so your file could look something like this

    "first_name": "<%= @user.first_name.to_json %>",
    "last_name": "<%= @user.last_name.to_json %>"

Checking if an object is null in C#

This was a good Example!

    if (MyObj is Object)
            //Do something .... for example:  
            if (MyObj is Button)
                MyObj.Enabled = true;

PHP Fatal error: Call to undefined function json_decode()



I installed PHP in Centos Docker, this is my DockerFile:

FROM centos:7.6.1810

LABEL maintainer="[email protected]"

RUN yum install httpd-2.4.6-88.el7.centos -y
RUN rpm -Uvh
RUN rpm -Uvh
RUN yum install php72w -y
ENTRYPOINT ["/usr/sbin/httpd", "-D", "FOREGROUND"]

The app returned the same error with json_decode and json_encode


Install PHP Common that has json_encode and json_decode

yum install -y php72w-common-7.2.14-1.w7.x86_64

How to find the resolution?

I have another Docker File what build the container for the API and it has the order to install php-mysql client:

yum install php72w-mysql.x86_64 -y

If i use these image to mount the app, the json_encode and json_decode works!! Ok..... What dependencies does this have?

[root@c023b46b720c etc]# yum install php72w-mysql.x86_64
Loaded plugins: fastestmirror, ovl
Loading mirror speeds from cached hostfile
 * base:
 * epel:
 * extras:
 * updates:
 * webtatic:
Resolving Dependencies
--> Running transaction check
---> Package php72w-mysql.x86_64 0:7.2.14-1.w7 will be installed
--> Processing Dependency: php72w-pdo(x86-64) for package: php72w-mysql-7.2.14-1.w7.x86_64
--> Processing Dependency: for package: php72w-mysql-7.2.14-1.w7.x86_64
--> Processing Dependency: for package: php72w-mysql-7.2.14-1.w7.x86_64
--> Running transaction check
---> Package mariadb-libs.x86_64 1:5.5.60-1.el7_5 will be installed
---> Package php72w-pdo.x86_64 0:7.2.14-1.w7 will be installed
--> Processing Dependency: php72w-common(x86-64) = 7.2.14-1.w7 for package: php72w-pdo-7.2.14-1.w7.x86_64
--> Running transaction check
---> Package php72w-common.x86_64 0:7.2.14-1.w7 will be installed
--> Finished Dependency Resolution

Dependencies Resolved

 Package                   Arch               Version                        Repository            Size
 php72w-mysql              x86_64             7.2.14-1.w7                    webtatic              82 k
Installing for dependencies:
 mariadb-libs              x86_64             1:5.5.60-1.el7_5               base                 758 k
 php72w-common             x86_64             7.2.14-1.w7                    webtatic             1.3 M
 php72w-pdo                x86_64             7.2.14-1.w7                    webtatic              89 k

Transaction Summary
Install  1 Package (+3 Dependent packages)

Total download size: 2.2 M
Installed size: 17 M
Is this ok [y/d/N]: y
Downloading packages:
(1/4): mariadb-libs-5.5.60-1.el7_5.x86_64.rpm                                    | 758 kB  00:00:00     
(2/4): php72w-mysql-7.2.14-1.w7.x86_64.rpm                                       |  82 kB  00:00:01     
(3/4): php72w-pdo-7.2.14-1.w7.x86_64.rpm                                         |  89 kB  00:00:01     
(4/4): php72w-common-7.2.14-1.w7.x86_64.rpm                                      | 1.3 MB  00:00:06     
Total                                                                   336 kB/s | 2.2 MB  00:00:06     
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
  Installing : 1:mariadb-libs-5.5.60-1.el7_5.x86_64                                                 1/4 
  Installing : php72w-common-7.2.14-1.w7.x86_64                                                     2/4 
  Installing : php72w-pdo-7.2.14-1.w7.x86_64                                                        3/4 
  Installing : php72w-mysql-7.2.14-1.w7.x86_64                                                      4/4 
  Verifying  : php72w-common-7.2.14-1.w7.x86_64                                                     1/4 
  Verifying  : 1:mariadb-libs-5.5.60-1.el7_5.x86_64                                                 2/4 
  Verifying  : php72w-pdo-7.2.14-1.w7.x86_64                                                        3/4 
  Verifying  : php72w-mysql-7.2.14-1.w7.x86_64                                                      4/4 

  php72w-mysql.x86_64 0:7.2.14-1.w7                                                                     

Dependency Installed:
  mariadb-libs.x86_64 1:5.5.60-1.el7_5                php72w-common.x86_64 0:7.2.14-1.w7               
  php72w-pdo.x86_64 0:7.2.14-1.w7                    


Yes! Inside the dependences is the common packages. I Installed it into my other container and it works! After, i put de directive into DockerFile, Git commit!! Git Tag!!!! Git Push!!!! Ready!

Error LNK2019 unresolved external symbol _main referenced in function "int __cdecl invoke_main(void)" (?invoke_main@@YAHXZ)

This worked for me:

(I don't have enough rep to embed pictures yet -- sorry about this.)

I went into Project --> Properties --> Linker --> System.

IMG: Located here, as of Dec 2019 Visual Studio for Windows

My platform was set to Active(Win32) with the Subsystem as "Windows". I was making a console app, so I set it to "Console".

IMG: Changing "Windows" --> "Console"

Then, I switched my platform to "x64".

IMG: Switched my platform from Active(32) to x64

How can I copy the content of a branch to a new local branch?

git checkout old_branch
git branch new_branch

This will give you a new branch "new_branch" with the same state as "old_branch".

This command can be combined to the following:

git checkout -b new_branch old_branch

Order discrete x scale by frequency/value

Hadley has been developing a package called forcats. This package makes the task so much easier. You can exploit fct_infreq() when you want to change the order of x-axis by the frequency of a factor. In the case of the mtcars example in this post, you want to reorder levels of cyl by the frequency of each level. The level which appears most frequently stays on the left side. All you need is the fct_infreq().


ggplot(mtcars, aes(fct_infreq(factor(cyl)))) +
geom_bar() +
labs(x = "cyl")

If you wanna go the other way around, you can use fct_rev() along with fct_infreq().

ggplot(mtcars, aes(fct_rev(fct_infreq(factor(cyl))))) +
geom_bar() +
labs(x = "cyl") 

enter image description here

String comparison technique used by Python

Python string comparison is lexicographic:

From Python Docs:

Strings are compared lexicographically using the numeric equivalents (the result of the built-in function ord()) of their characters. Unicode and 8-bit strings are fully interoperable in this behavior.

Hence in your example, 'abc' < 'bac', 'a' comes before (less-than) 'b' numerically (in ASCII and Unicode representations), so the comparison ends right there.

show distinct column values in pyspark dataframe: python

This should help to get distinct values of a column:'column1').distinct().collect()

Note that .collect() doesn't have any built-in limit on how many values can return so this might be slow -- use .show() instead or add .limit(20) before .collect() to manage this.

Java socket API: How to tell if a connection has been closed?

As @user207421 say there is no way to know the current state of the connection because of the TCP/IP Protocol Architecture Model. So the server has to notice you before closing the connection or you check it by yourself.
This is a simple example that shows how to know the socket is closed by the server:

sockAdr = new InetSocketAddress(SERVER_HOSTNAME, SERVER_PORT);
socket = new Socket();
timeout = 5000;
socket.connect(sockAdr, timeout);
reader = new BufferedReader(new InputStreamReader(socket.getInputStream());
while ((data = reader.readLine())!=null) 
      log.e(TAG, "received -> " + data);
log.e(TAG, "Socket closed !");

Difference between applicationContext.xml and spring-servlet.xml in Spring Framework

Spring lets you define multiple contexts in a parent-child hierarchy.

The applicationContext.xml defines the beans for the "root webapp context", i.e. the context associated with the webapp.

The spring-servlet.xml (or whatever else you call it) defines the beans for one servlet's app context. There can be many of these in a webapp, one per Spring servlet (e.g. spring1-servlet.xml for servlet spring1, spring2-servlet.xml for servlet spring2).

Beans in spring-servlet.xml can reference beans in applicationContext.xml, but not vice versa.

All Spring MVC controllers must go in the spring-servlet.xml context.

In most simple cases, the applicationContext.xml context is unnecessary. It is generally used to contain beans that are shared between all servlets in a webapp. If you only have one servlet, then there's not really much point, unless you have a specific use for it.

jQuery: what is the best way to restrict "number"-only input for textboxes? (allow decimal points)

You can use HTML5 validation on your text inputs by adding a pattern. No need to manually validate with regex or keyCodes.

<input type="text" pattern="[0-9.]+" />

$("input[type=text][pattern]").on("input", function () {
    if (!this.checkValidity())
        this.value = this.value.slice(0, -1);

For a solution with input [type=number], see my full answer here

How to fix "Only one expression can be specified in the select list when the subquery is not introduced with EXISTS" error?

Try this one -

       ID, Salt, password, BannedEndDate
     , (
          SELECT COUNT(1)
          FROM dbo.LoginFails l
          WHERE l.UserName = u.UserName
               AND IP = '" + Request.ServerVariables["REMOTE_ADDR"] + "'
      ) AS cnt
FROM dbo.Users u
WHERE u.UserName = '" + LoginModel.Username + "'"

Should I use alias or alias_method?

alias_method can be redefined if need be. (it's defined in the Module class.)

alias's behavior changes depending on its scope and can be quite unpredictable at times.

Verdict: Use alias_method - it gives you a ton more flexibility.


def foo

alias_method :baz, :foo

How would you make two <div>s overlap?

If you want the logo to take space, you are probably better of floating it left and then moving down the content using margin, sort of like this:

#logo {
    float: left;
    margin: 0 10px 10px 20px;

#content {
    margin: 10px 0 0 10px;

or whatever margin you want.

How to convert a file into a dictionary?

IMHO a bit more pythonic to use generators (probably you need 2.7+ for this):

with open('infile.txt') as fd:
    pairs = (line.split(None) for line in fd)
    res   = {int(pair[0]):pair[1] for pair in pairs if len(pair) == 2 and pair[0].isdigit()}

This will also filter out lines not starting with an integer or not containing exactly two items

IPython/Jupyter Problems saving notebook as PDF

2015-4-22: It looks like an IPython update means that --to pdf should be used instead of --to latex --post PDF. There is a related Github issue.

How to create our own Listener interface in android?

Simple method to do this approach. Firstly implements the OnClickListeners in your Activity class.


class MainActivity extends Activity implements OnClickListeners{

protected void OnCreate(Bundle bundle)
    Button b1=(Button)findViewById(;    
    Button b2=(Button)findViewById(;    

public void OnClick(View V)    
    int i=v.getId();    
            //you can do anything from this button
            //you can do anything from this button       

Can someone explain the dollar sign in Javascript?

A '$' in a variable means nothing special to the interpreter, much like an underscore.

From what I've seen, many people using jQuery (which is what your example code looks like to me) tend to prefix variables that contain a jQuery object with a $ so that they are easily identified and not mixed up with, say, integers.

The dollar sign function $() in jQuery is a library function that is frequently used, so a short name is desirable.

What is the maximum length of data I can put in a BLOB column in MySQL?

A BLOB can be 65535 bytes (64 KB) maximum.

If you need more consider using:

  • a MEDIUMBLOB for 16777215 bytes (16 MB)

  • a LONGBLOB for 4294967295 bytes (4 GB).

See Storage Requirements for String Types for more info.

How to plot two columns of a pandas data frame using points?

Pandas uses matplotlib as a library for basic plots. The easiest way in your case will using the following:

import pandas as pd
import numpy as np

#creating sample data 
      'col_name_2': np.random.rand(20)}
df= pd.DataFrame(sample_data)
df.plot(x='col_name_1', y='col_name_2', style='o')

enter image description here

However, I would recommend to use seaborn as an alternative solution if you want have more customized plots while not going into the basic level of matplotlib. In this case you the solution will be following:

import pandas as pd
import seaborn as sns
import numpy as np

#creating sample data 
      'col_name_2': np.random.rand(20)}
df= pd.DataFrame(sample_data)
sns.scatterplot(x="col_name_1", y="col_name_2", data=df)

enter image description here

Apache POI Excel - how to configure columns to be expanded?

You can wrap the text as well. PFB sample code:

CellStyle wrapCellStyle = new_workbook.createCellStyle();

Shell script to check if file exists

One approach:

  shopt -s nullglob
  if [[ "${#files[@]}" -gt 0 ]] ; then
    echo found one
    echo found none


  • shopt -s nullglob will cause /home/edward/bank1/fiche/Test* to expand to nothing if no file matches that pattern. (Without it, it will be left intact.)
  • ( ... ) sets up a subshell, preventing shopt -s nullglob from "escaping".
  • files=(/home/edward/bank1/fiche/Test*) puts the file-list in an array named files. (Note that this is within the subshell only; files will not be accessible after the subshell exits.)
  • "${#files[@]}" is the number of elements in this array.

Edited to address subsequent question ("What if i also need to check that these files have data in them and are not zero byte files"):

For this version, we need to use -s (as you did in your question), which also tests for the file's existence, so there's no point using shopt -s nullglob anymore: if no file matches the pattern, then -s on the pattern will be false. So, we can write:

  for file in /home/edward/bank1/fiche/Test* ; do
    if [[ -s "$file" ]] ; then
  if [[ "$found_nonempty" ]] ; then
    echo found one
    echo found none

(Here the ( ... ) is to prevent file and found_file from "escaping".)

"OSError: [Errno 1] Operation not permitted" when installing Scrapy in OSX 10.11 (El Capitan) (System Integrity Protection)

install python again:

brew install python

try it again:

sudo pip install scrapy

works for me, hope it can help

Call An Asynchronous Javascript Function Synchronously

You can also convert it into callbacks.

function thirdPartyFoo(callback) {    
  callback("Hello World");    

function foo() {    
  var fooVariable;

  thirdPartyFoo(function(data) {
    fooVariable = data;

  return fooVariable;

var temp = foo();  

How to run PowerShell in CMD

I'd like to add the following to Shay Levy's correct answer: You can make your life easier if you create a little batch script run.cmd to launch your powershell script:

@echo off & setlocal
set batchPath=%~dp0
powershell.exe -noexit -file "%batchPath%SQLExecutor.ps1" "MY-PC"

Put it in the same path as SQLExecutor.ps1 and from now on you can run it by simply double-clicking on run.cmd.


  • If you require command line arguments inside the run.cmd batch, simply pass them as %1 ... %9 (or use %* to pass all parameters) to the powershell script, i.e.
    powershell.exe -noexit -file "%batchPath%SQLExecutor.ps1" %*

  • The variable batchPath contains the executing path of the batch file itself (this is what the expression %~dp0 is used for). So you just put the powershell script in the same path as the calling batch file.

Measure the time it takes to execute a t-sql query

One simplistic approach to measuring the "elapsed time" between events is to just grab the current date and time.

In SQL Server Management Studio

SELECT /* query one */ 1 ;
SELECT /* query two */ 2 ; 

To calculate elapsed times, you could grab those date values into variables, and use the DATEDIFF function:


SET @t1 = GETDATE();
SELECT /* query one */ 1 ;
SET @t2 = GETDATE();
SELECT DATEDIFF(millisecond,@t1,@t2) AS elapsed_ms;

SET @t1 = GETDATE();
SELECT /* query two */ 2 ;
SET @t2 = GETDATE();
SELECT DATEDIFF(millisecond,@t1,@t2) AS elapsed_ms;

That's just one approach. You can also get elapsed times for queries using SQL Profiler.

Default behavior of "git push" without a branch specified

You can set up default behavior for your git with push.default

git config push.default current

or if you have many repositories and want the same for all then

git config --global push.default current

The current in this setup means that by default you will only push the current branch when you do git push

Other options are:

  • nothing : Do not push anything
  • matching : Push all matching branches (default)
  • tracking : Push the current branch to whatever it is tracking
  • current : Push the current branch


As of Git 1.7.11 do the following:

git config --global push.default simple

This is a new setting introduced that works in the same way as current, and will be made default to git from v 2.0 according to rumors

re.sub erroring with "Expected string or bytes-like object"

I suppose better would be to use re.match() function. here is an example which may help you.

import re
import nltk
from nltk.tokenize import word_tokenize'punkt')
sentences = word_tokenize("I love to learn NLP \n 'a :(")
#for i in range(len(sentences)):
sentences = [word.lower() for word in sentences if re.match('^[a-zA-Z]+', word)]  

Catch a thread's exception in the caller thread in Python

The problem is that thread_obj.start() returns immediately. The child thread that you spawned executes in its own context, with its own stack. Any exception that occurs there is in the context of the child thread, and it is in its own stack. One way I can think of right now to communicate this information to the parent thread is by using some sort of message passing, so you might look into that.

Try this on for size:

import sys
import threading
import Queue

class ExcThread(threading.Thread):

    def __init__(self, bucket):
        self.bucket = bucket

    def run(self):
            raise Exception('An error occured here.')
        except Exception:

def main():
    bucket = Queue.Queue()
    thread_obj = ExcThread(bucket)

    while True:
            exc = bucket.get(block=False)
        except Queue.Empty:
            exc_type, exc_obj, exc_trace = exc
            # deal with the exception
            print exc_type, exc_obj
            print exc_trace

        if thread_obj.isAlive():

if __name__ == '__main__':

Select query to get data from SQL Server

You should use ExecuteScalar() (which returns the first row first column) instead of ExecuteNonQuery() (which returns the no. of rows affected).

You should refer differences between executescalar and executenonquery for more details.

Hope it helps!

Create pandas Dataframe by appending one row at a time

You can also build up a list of lists and convert it to a dataframe -

import pandas as pd

columns = ['i','double','square']
rows = []

for i in range(6):
    row = [i, i*2, i*i]

df = pd.DataFrame(rows, columns=columns)


    i   double  square
0   0   0   0
1   1   2   1
2   2   4   4
3   3   6   9
4   4   8   16
5   5   10  25

WebView and HTML5 <video>

I answer this topic just in case someone read it and is interested on the result. It is possible to view a video element (video html5 tag) within a WebView, but I must say I had to deal with it for few days. These are the steps I had to follow so far:

-Find a properly encoded video

-When initializing the WebView, set the JavaScript, Plug-ins the WebViewClient and the WebChromeClient.

url = new String(""); 
mWebView = (WebView) findViewById(;

-Handle the onShowCustomView in the WebChromeClient object.

public void onShowCustomView(View view, CustomViewCallback callback) {
    super.onShowCustomView(view, callback);
    if (view instanceof FrameLayout){
        FrameLayout frame = (FrameLayout) view;
        if (frame.getFocusedChild() instanceof VideoView){
            VideoView video = (VideoView) frame.getFocusedChild();

-Handle the onCompletion and the onError events for the video, in order to get back to the web view.

public void onCompletion(MediaPlayer mp) {
    Log.d(TAG, "Video completo");
    WebView wb = (WebView) a.findViewById(;

But now I should say there are still an important issue. I can play it only once. The second time I click on the video dispatcher (either the poster or some play button), it does nothing.

I would also like the video to play inside the WebView frame, instead of opening the Media Player window, but this is for me a secondary issue.

I hope it helps somebody, and I would also thank any comment or suggestion.

Saludos, terrícolas.

Laravel 5.4 ‘cross-env’ Is Not Recognized as an Internal or External Command

Just npm install --save-dev cross-env in the root directory of your project.

How do I access ViewBag from JS

if you are using razor engine template then do the following

in your view write :

<script> var myJsVariable = '@ViewBag.MyVariable' </script>

UPDATE: A more appropriate approach is to define a set of configuration on the master layout for example, base url, facebook API Key, Amazon S3 base URL, etc ...```

   var AppConfig = @Html.Raw(Json.Encode(new {
    baseUrl: Url.Content("~"),
    fbApi: "get it from db",
    awsUrl: "get it from db"

And you can use it in your JavaScript code as follow:

  myProduct.fullUrl = AppConfig.awsUrl + myProduct.path;

send/post xml file using curl command line

Powershell + Curl + Zimbra SOAP API

${my_xml} = @"
<?xml version=\"1.0\" encoding=\"UTF-8\"?>
<soapenv:Envelope xmlns:soapenv=\"\">
   <GetFolderRequest xmlns=\"urn:zimbraMail\">
       <path>Folder Name</path>

${my_curl} = "c:\curl.exe"
${cookie} = "c:\cookie.txt"

${zimbra_soap_url} = "https://zimbra:7071/service/admin/soap"
${curl_getfolder_args} = "-b", "${cookie}",
            "--header", "Content-Type: text/xml;charset=UTF-8",
            "--data-raw", "${my_xml}",
            "--url", "${zimbra_soap_url}"

[xml]${my_response} = & ${my_curl} ${curl_getfolder_args}

Filling a List with all enum values in Java

There is a constructor for ArrayList which is

ArrayList(Collection<? extends E> c) 

Now, EnumSet extends AbstractCollection so you can just do

ArrayList<Something> all = new ArrayList<Something>(enumSet)

Spring Boot @autowired does not work, classes in different package

Just put the packages inside the @SpringBootApplication tag.

@SpringBootApplication(scanBasePackages = { "com.pkg1", "com.pkg2", .....})

Let me know.

How do I make a MySQL database run completely in memory?

Memory Engine is not the solution you're looking for. You lose everything that you went to a database for in the first place (i.e. ACID).

Here are some better alternatives:

  1. Don't use joins - very few large apps do this (i.e Google, Flickr, NetFlix), because it sucks for large sets of joins.

A LEFT [OUTER] JOIN can be faster than an equivalent subquery because the server might be able to optimize it better—a fact that is not specific to MySQL Server alone.

-The MySQL Manual

  1. Make sure the columns you're querying against have indexes. Use EXPLAIN to confirm they are being used.
  2. Use and increase your Query_Cache and memory space for your indexes to get them in memory and store frequent lookups.
  3. Denormalize your schema, especially for simple joins (i.e. get fooId from barMap).

The last point is key. I used to love joins, but then had to run joins on a few tables with 100M+ rows. No good. Better off insert the data you're joining against into that target table (if it's not too much) and query against indexed columns and you'll get your query in a few ms.

I hope those help.

"unexpected token import" in Nodejs5 and babel?

  1. Install packages: babel-core, babel-polyfill, babel-preset-es2015
  2. Create .babelrc with contents: { "presets": ["es2015"] }
  3. Do not put import statement in your main entry file, use another file eg: app.js and your main entry file should required babel-core/register and babel-polyfill to make babel works separately at the first place before anything else. Then you can require app.js where import statement.





import co from 'co';

It should works with node index.js.

How do I generate a stream from a string?

I think you can benefit from using a MemoryStream. You can fill it with the string bytes that you obtain by using the GetBytes method of the Encoding class.

How to get the home directory in Python?

You want to use os.path.expanduser.
This will ensure it works on all platforms:

from os.path import expanduser
home = expanduser("~")

If you're on Python 3.5+ you can use pathlib.Path.home():

from pathlib import Path
home = str(Path.home())

How to move git repository with all branches from bitbucket to github?

It's very simple.

  1. Create a new empty repository in GitHub (without readme or license, you can add them later) and the following screen will show.

  2. In the import code option, paste your Bitbucket repo's URL and voilà!!

Click Import code

How to compare timestamp dates with date-only parameter in MySQL?

You can use the DATE() function to extract the date portion of the timestamp:

WHERE DATE(timestamp) = '2012-05-25'

Though, if you have an index on the timestamp column, this would be faster because it could utilize an index on the timestamp column if you have one:

WHERE timestamp BETWEEN '2012-05-25 00:00:00' AND '2012-05-25 23:59:59'

Reading a text file with SQL Server

BULK INSERT dbo.temp 

FROM 'c:\temp\file.txt' --- path file in db server 



it work for me but save as by editplus to ansi encoding for multilanguage

Laravel 5 – Remove Public from URL

Another method that I use is to create a symbolic link (in Linux, don't know about Win) using the ln command in htdocs or www i.e. ln projectname/public project The site is thus accessible via localhost/project

Python: Tuples/dictionaries as keys, select, sort

This type of data is efficiently pulled from a Trie-like data structure. It also allows for fast sorting. The memory efficiency might not be that great though.

A traditional trie stores each letter of a word as a node in the tree. But in your case your "alphabet" is different. You are storing strings instead of characters.

it might look something like this:

root:                Root
                    / | \
                   /  |  \     
fruit:       Banana Apple Strawberry
              / |      |     \
             /  |      |      \
color:     Blue Yellow Green  Blue
            /   |       |       \
           /    |       |        \
end:      24   100      12        0

see this link: trie in python

CSS Styling for a Button: Using <input type="button> instead of <button>

In your .button CSS, try display:inline-block. See this JSFiddle

How to dynamically create a class?

Runtime Code Generation with JVM and CLR - Peter Sestoft

Work for persons that are really interested in this type of programming.

My tip for You is that if You declare something try to avoid string, so if You have class Field it is better to use class System.Type to store the field type than a string. And for the sake of best solutions instead of creation new classes try to use those that has been created FiledInfo instead of creation new.

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

double click the button and add write // this.close();

  private void buttonClick(object sender, EventArgs e)

Slidedown and slideup layout with animation

This doesn't work for me, I want to to like jquery slideUp / slideDown function, I tried this code, but it only move the content wich stay at the same place after animation end, the view should have a 0dp height at start of slideDown and the view height (with wrap_content) after the end of the animation.

Why doesn't RecyclerView have onItemClickListener()?

Here is a way to implement it quite easily if you have a list of POJOs and want to retrieve one on click from outside the adapter.

In your adapter, create a listener for the click events and a method to set it:

public class MyAdapter extends RecyclerView.Adapter<SitesListAdapter.ViewHolder> {
private List<MyPojo> mMyPojos;
private static OnItemClickListener mOnItemClickListener;

public interface OnItemClickListener {
    public void onItemClick(MyPojo pojo);

public void setOnItemClickListener(OnItemClickListener onItemClickListener){
    mOnItemClickListener = onItemClickListener;


In your ViewHolder, implement onClickListener and create a class member to temporarily store the POJO the view is presenting, that way (this is an example, creating a setter would be better):

public static class ViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {
    public MyPojo mCurrentPojo;
    public ViewHolder(View view) {
        view.setOnClickListener(this); //You could set this on part of the layout too

    public void onClick(View view) {
        if(mOnItemClickListener != null && mCurrentPojo != null){

Back in your adapter, set the current POJO when the ViewHolder is bound (or to null if the current view doesn't have one):

public void onBindViewHolder(final ViewHolder holder, final int position) {
    final MyPojo currentPojo = mMyPojos.get(position); 
    holder.mCurrentPojo = currentPojo;

That's it, now you can use it like this from your fragment/activity:

    mMyAdapter.setOnItemClickListener(new mMyAdapter.OnItemClickListener() {
        public void onItemClick(MyPojo pojo) {
            //Do whatever you want with your pojo here

How do I use tools:overrideLibrary in a build.gradle file?

use this code in manifest.xml


Is there a "previous sibling" selector?

I had the same question, but then I had a "duh" moment. Instead of writing

x ~ y


y ~ x

Obviously this matches "x" instead of "y", but it answers the "is there a match?" question, and simple DOM traversal may get you to the right element more efficiently than looping in javascript.

I realize that the original question was a CSS question so this answer is probably completely irrelevant, but other Javascript users may stumble on the question via search like I did.

How to use router.navigateByUrl and router.navigate in Angular


routerLink directive as used like this:

<a [routerLink]="/inbox/33/messages/44">Open Message 44</a>

is just a wrapper around imperative navigation using router and its navigateByUrl method:


as can be seen from the sources:

export class RouterLink {

  onClick(): boolean {
    this.router.navigateByUrl(this.urlTree, extras);
    return true;

So wherever you need to navigate a user to another route, just inject the router and use navigateByUrl method:

class MyComponent {
   constructor(router: Router) {


There's another method on the router that you can use - navigate:


difference between the two

Using router.navigateByUrl is similar to changing the location bar directly–we are providing the “whole” new URL. Whereas router.navigate creates a new URL by applying an array of passed-in commands, a patch, to the current URL.

To see the difference clearly, imagine that the current URL is '/inbox/11/messages/22(popup:compose)'.

With this URL, calling router.navigateByUrl('/inbox/33/messages/44') will result in '/inbox/33/messages/44'. But calling it with router.navigate(['/inbox/33/messages/44']) will result in '/inbox/33/messages/44(popup:compose)'.

Read more in the official docs.

How much faster is C++ than C#?

There is no strict reason why a bytecode based language like C# or Java that has a JIT cannot be as fast as C++ code. However C++ code used to be significantly faster for a long time, and also today still is in many cases. This is mainly due to the more advanced JIT optimizations being complicated to implement, and the really cool ones are only arriving just now.

So C++ is faster, in many cases. But this is only part of the answer. The cases where C++ is actually faster, are highly optimized programs, where expert programmers thoroughly optimized the hell out of the code. This is not only very time consuming (and thus expensive), but also commonly leads to errors due to over-optimizations.

On the other hand, code in interpreted languages gets faster in later versions of the runtime (.NET CLR or Java VM), without you doing anything. And there are a lot of useful optimizations JIT compilers can do that are simply impossible in languages with pointers. Also, some argue that garbage collection should generally be as fast or faster as manual memory management, and in many cases it is. You can generally implement and achieve all of this in C++ or C, but it's going to be much more complicated and error prone.

As Donald Knuth said, "premature optimization is the root of all evil". If you really know for sure that your application will mostly consist of very performance critical arithmetic, and that it will be the bottleneck, and it's certainly going to be faster in C++, and you're sure that C++ won't conflict with your other requirements, go for C++. In any other case, concentrate on first implementing your application correctly in whatever language suits you best, then find performance bottlenecks if it runs too slow, and then think about how to optimize the code. In the worst case, you might need to call out to C code through a foreign function interface, so you'll still have the ability to write critical parts in lower level language.

Keep in mind that it's relatively easy to optimize a correct program, but much harder to correct an optimized program.

Giving actual percentages of speed advantages is impossible, it largely depends on your code. In many cases, the programming language implementation isn't even the bottleneck. Take the benchmarks at with a great deal of scepticism, as these largely test arithmetic code, which is most likely not similar to your code at all.

Where does Visual Studio look for C++ header files?

Actually On my windows 10 with visual studio 2017 community, the C++ headers path are:

  1. C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Tools\MSVC\14.15.26726\include

  2. C:\Program Files (x86)\Windows Kits\10\Include\10.0.17134.0\ucrt

The 1st contains standard C++ headers such as <iostream>, <algorithm>. The 2nd contains old C headers such as <stdio.h>, <string.h>. The version number can be different based on your software.

Hope this would help.

"FATAL: Module not found error" using modprobe

Ensure that your network is brought down before loading module:

sudo stop networking

It helped me -

Getting the difference between two Dates (months/days/hours/minutes/seconds) in Swift

For XCode Version 8.3.3 & Swift 3.0:

    let dateFormatter = DateFormatter()
    dateFormatter.dateStyle = .medium
    dateFormatter.timeStyle = .short

    var beginDate = "2017-08-24 12:00:00"
    var endDate = "2017-09-07 12:00:00"

    let startDateTime = beginDate) //according to date format your date string
    print(startDateTime ?? "") //Convert String to Date

    let endDateTime = endDate) //according to date format your date string
    print(endDateTime ?? "") //Convert String to Date

    let dateComponentsFormatter = DateComponentsFormatter()
    dateComponentsFormatter.allowedUnits = [NSCalendar.Unit.minute,NSCalendar.Unit.hour,]

   let interval = endDateTime!.timeIntervalSince(startDateTime!)
   var diff = dateComponentsFormatter.string(from: interval)!


   var day_i  = 0
   var hour_i = 0
   var min_i = 0

     if (diff.contains("d"))
              let day = diff.substring(to: (diff.range(of: "d")?.lowerBound)!)

               day_i  = Int(day)!
               print ("day --> \(day_i)")

               diff = diff.substring(from:(diff.range(of : " ")?.upperBound )!)

       let hour = diff.substring(to: (diff.range(of : ":")?.lowerBound )!)
       hour_i  = Int(hour)!
       print ("hour --> \(hour_i)")

       let min = diff.substring(from: (diff.range(of : ":")?.upperBound )!)
       min_i  = Int(min)!
       print ("min --> \(min_i)")

Download pdf file using jquery ajax

I am newbie and most of the code is from google search. I got my pdf download working with the code below (trial and error play). Thank you for code tips (xhrFields) above.

            cache: false,
            type: 'POST',
            url: 'yourURL',
            contentType: false,
            processData: false,
            data: yourdata,
             //xhrFields is what did the trick to read the blob to pdf
            xhrFields: {
                responseType: 'blob'
            success: function (response, status, xhr) {

                var filename = "";                   
                var disposition = xhr.getResponseHeader('Content-Disposition');

                 if (disposition) {
                    var filenameRegex = /filename[^;=\n]*=((['"]).*?\2|[^;\n]*)/;
                    var matches = filenameRegex.exec(disposition);
                    if (matches !== null && matches[1]) filename = matches[1].replace(/['"]/g, '');
                var linkelem = document.createElement('a');
                try {
                                           var blob = new Blob([response], { type: 'application/octet-stream' });                        

                    if (typeof window.navigator.msSaveBlob !== 'undefined') {
                        //   IE workaround for "HTML7007: One or more blob URLs were revoked by closing the blob for which they were created. These URLs will no longer resolve as the data backing the URL has been freed."
                        window.navigator.msSaveBlob(blob, filename);
                    } else {
                        var URL = window.URL || window.webkitURL;
                        var downloadUrl = URL.createObjectURL(blob);

                        if (filename) { 
                            // use HTML5 a[download] attribute to specify filename
                            var a = document.createElement("a");

                            // safari doesn't support this yet
                            if (typeof === 'undefined') {
                                window.location = downloadUrl;
                            } else {
                                a.href = downloadUrl;
                       = filename;
                       = "_blank";
                        } else {
                            window.location = downloadUrl;

                } catch (ex) {

Android: textview hyperlink


    android:text="" />

This flag


controls whether links such as urls automatically found and converted to clickable links. The default value is "none", disabling this feature. Values: all, email, map, none, phone, web.

R Plotting confidence bands with ggplot


mp <-data.frame(year=1990:2010)
N <- nrow(mp)

mp <- within(mp,
             wav <- rnorm(N)*cos(2*pi*year)+rnorm(N)*sin(2*pi*year)+5
             wow <- rnorm(N)*wav+rnorm(N)*wav^3

m01 <- gls(wow~poly(wav,3), data=mp, correlation = corARMA(p=1))

Get fitted values (the same as m01$fitted)

fit <- predict(m01)

Normally we could use something like predict(..., to get the confidence intervals on the prediction, but gls doesn't provide this capability. We use a recipe similar to the one shown at :

V <- vcov(m01)
X <- model.matrix(~poly(wav,3),data=mp) <- sqrt(diag(X %*% V %*% t(X)))

Put together a "prediction frame":

predframe <- with(mp,data.frame(year,wav,

Now plot with geom_ribbon

(p1 <- ggplot(mp, aes(year, wow))+

year vs wow

It's easier to see that we got the right answer if we plot against wav rather than year:

(p2 <- ggplot(mp, aes(wav, wow))+

wav vs wow

It would be nice to do the predictions with more resolution, but it's a little tricky to do this with the results of poly() fits -- see ?makepredictcall.

What is causing ImportError: No module named pkg_resources after upgrade of Python on os X?

I encountered the same ImportError. Somehow the setuptools package had been deleted in my Python environment.

To fix the issue, run the setup script for setuptools:

curl | python

If you have any version of distribute, or any setuptools below 0.6, you will have to uninstall it first.*

See Installation Instructions for further details.

* If you already have a working distribute, upgrading it to the "compatibility wrapper" that switches you over to setuptools is easier. But if things are already broken, don't try that.

Android: disabling highlight on listView click

Add this to your xml:


And for the problem this may work (I'm not sure and I don't know if there are better solutions):

You could apply a ColorStateList to your TextView.

How to create/read/write JSON files in Qt5

An example on how to use that would be great. There is a couple of examples at the Qt forum, but you're right that the official documentation should be expanded.

QJsonDocument on its own indeed doesn't produce anything, you will have to add the data to it. That's done through the QJsonObject, QJsonArray and QJsonValue classes. The top-level item needs to be either an array or an object (because 1 is not a valid json document, while {foo: 1} is.)

What is the difference between JAX-RS and JAX-WS?

i have been working on Apachi Axis1.1 and Axis2.0 and JAX-WS but i would suggest you must JAX-WS because it allow you make wsdl in any format , i was making operation as GetInquiry() in Apache Axis2 it did not allow me to Start Operation name in Upper Case , so i find it not good , so i would suggest you must use JAX-WS

How do I check if there are duplicates in a flat list?

Recommended for short lists only:

any(thelist.count(x) > 1 for x in thelist)

Do not use on a long list -- it can take time proportional to the square of the number of items in the list!

For longer lists with hashable items (strings, numbers, &c):

def anydup(thelist):
  seen = set()
  for x in thelist:
    if x in seen: return True
  return False

If your items are not hashable (sublists, dicts, etc) it gets hairier, though it may still be possible to get O(N logN) if they're at least comparable. But you need to know or test the characteristics of the items (hashable or not, comparable or not) to get the best performance you can -- O(N) for hashables, O(N log N) for non-hashable comparables, otherwise it's down to O(N squared) and there's nothing one can do about it:-(.

How to combine two strings together in PHP?

Concatenate them with the . operator:

$result = $data1 . " " . $data2;

Or use string interpolation:

$result = "$data1 $data2";

Intellij JAVA_HOME variable

Bit counter-intuitive, but you must first setup a SDK for Java projects. On the bottom right of the IntelliJ welcome screen, select 'Configure > Project Defaults > Project Structure'.

The Project tab on the left will show that you have no SDK selected:

Therefore, you must click the 'New...' button on the right hand side of the dropdown and point it to your JDK. After that, you can go back to the import screen and it should be populated with your JAVA_HOME variable, providing you have this set.

How can I customize the tab-to-space conversion factor?

In Visual Studio Code version 1.31.1 or later (I think): Like sed Alex Dima, you can customize this easily via these settings for

  • Windows in menu File ? Preferences ? User Settings or use short keys Ctrl + Shift + P
  • Mac in menu Code ? Preferences ? Settings or ?,

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How do you send a Firebase Notification to all devices via CURL?

For anyone wondering how to do it in cordova hybrid app:

  • go to index.js -> inside the function onDeviceReady() write :


(It's important to write it at the top of the function!)

  • then, in the same file (index.js) find :

    function subscribe(){

     FirebasePlugin.subscribe("write_here_your_topic", function(){
         logError("Failed to subscribe to topic", error);

and write your own topic here -> "write_here_your_topic"

What does java.lang.Thread.interrupt() do?

Thread interruption is based on flag interrupt status. For every thread default value of interrupt status is set to false. Whenever interrupt() method is called on thread, interrupt status is set to true.

  1. If interrupt status = true (interrupt() already called on thread), that particular thread cannot go to sleep. If sleep is called on that thread interrupted exception is thrown. After throwing exception again flag is set to false.
  2. If thread is already sleeping and interrupt() is called, thread will come out of sleeping state and throw interrupted Exception.

Correct redirect URI for Google API and OAuth 2.0

There's no problem with using a localhost url for Dev work - obviously it needs to be changed when it comes to production.

You need to go here: and then follow the link for the API Console - link's in the Basic Steps section. When you've filled out the new application form you'll be asked to provide a redirect Url. Put in the page you want to go to once access has been granted.

When forming the Google oAuth Url - you need to include the redirect url - it has to be an exact match or you'll have problems. It also needs to be UrlEncoded.

Is there an equivalent of lsusb for OS X

On Mac OS X, the Xcode developer suite includes the USB application. This is found in /Developer/Applications/Utilities/. USB Prober will allow you to examine the device and interface descriptors.

how to print float value upto 2 decimal place without rounding off

The only easy way to do this is to use snprintf to print to a buffer that's long enough to hold the entire, exact value, then truncate it as a string. Something like:

char buf[2*(DBL_MANT_DIG + DBL_MAX_EXP)];
snprintf(buf, sizeof buf, "%.*f", (int)sizeof buf, x);
char *p = strchr(buf, '.'); // beware locale-specific radix char, though!
p[2+1] = 0;

Text overwrite in visual studio 2010

None of the solutions above were working for me. My workaround was to open the on-screen keyboard using the system settings (press Windows key and search for "keyboard" to find them). Once that's open you can click the Insert key on it.

Root password inside a Docker container

Eventually, I decided to rebuild my Docker images, so that I change the root password by something I will know.

RUN echo 'root:Docker!' | chpasswd


RUN echo 'Docker!' | passwd --stdin root 

Redirecting to authentication dialog - "An error occurred. Please try again later"

I just encountered this problem myself. I'm developing an app internally, so my host is 'localhost'. It wasn't obvious how to set 'localhost' up in the app configuration. If you want to develop locally, set up your app by following these steps:

  1. Go to the place where you manage your Facebook app. Specifically, you want to be in "Basic" under the "Settings" menu.
  2. Add 'localhost' to "App Domain".
  3. Under "Select how your app integrates with Facebook", select "Website", and enter "http://localhost/".

Save and wait a couple of minutes for the information to propagate, although it worked right away for me.

Naming Conventions: What to name a boolean variable?




Maybe too wordy but they may help give you ideas.

Highlight Anchor Links when user manually scrolls?

You can use Jquery's on method and listen for the scroll event.

How can I close a login form and show the main form without my application closing?

Try this:

public void ShowMain()
        if(auth()) // a method that returns true when the user exists.
            System.Threading.Thread t = new System.Threading.Thread(new System.Threading.ThreadStart(Main));
            MessageBox.Show("Invalid login details.");
   public void Main()
      Application.Run(new Main());


You must call the new form in a diferent thread apartment, if I not wrong, because of the call system of windows' API and COM interfaces.

One advice: this system is high insecure, because you can change the if condition (in MSIL) and it's "a children game" to pass out your security. You need a stronger system to secure your software like obfuscate or remote login or something like this.

Hope this helps.