Programs & Examples On #Django aggregation

django-aggregation refers to an ability to aggregate a collection of objects provided by Django database-abstraction API

XAMPP - Error: MySQL shutdown unexpectedly

To resolve this,

Go to your XAMPP folder,

XAMPP -> mysql -> bin -> "my.ini"

After opening my.ini configuration file, Replace 3306 with 3308 in couple of places, because 3308 is a free port.

XAMPP -> php -> "php.ini"

Do the same as you did in "my.ini" file which is changing port 3306 to 3308.

Then, restart the XAMPP server.

It works fine.

Creating a static class with no instances

Seems that you need classmethod:

class World(object):

    allAirports = []

    def initialize(cls):

        if not cls.allAirports:
            f = open(os.path.expanduser("~/Desktop/1000airports.csv"))
            file_reader = csv.reader(f)

            for col in file_reader:

        return cls.allAirports

jQuery select all except first

My answer is focused to a extended case derived from the one exposed at top.

Suppose you have group of elements from which you want to hide the child elements except first. As an example:

  <div class='some-group'>
     <div class='child child-0'>visible#1</div>
     <div class='child child-1'>xx</div>
     <div class='child child-2'>yy</div>
  <div class='some-group'>
     <div class='child child-0'>visible#2</div>
     <div class='child child-1'>aa</div>
     <div class='child child-2'>bb</div>
  1. We want to hide all .child elements on every group. So this will not help because will hide all .child elements except visible#1:

  2. The solution (in this extended case) will be:


Speed up rsync with Simultaneous/Concurrent File Transfers?

rsync transfers files as fast as it can over the network. For example, try using it to copy one large file that doesn't exist at all on the destination. That speed is the maximum speed rsync can transfer data. Compare it with the speed of scp (for example). rsync is even slower at raw transfer when the destination file exists, because both sides have to have a two-way chat about what parts of the file are changed, but pays for itself by identifying data that doesn't need to be transferred.

A simpler way to run rsync in parallel would be to use parallel. The command below would run up to 5 rsyncs in parallel, each one copying one directory. Be aware that the bottleneck might not be your network, but the speed of your CPUs and disks, and running things in parallel just makes them all slower, not faster.

run_rsync() {
    # e.g. copies /main/files/blah to /main/filesTest/blah
    rsync -av "$1" "/main/filesTest/${1#/main/files/}"
export -f run_rsync
parallel -j5 run_rsync ::: /main/files/*

Caused by: org.flywaydb.core.api.FlywayException: Validate failed. Migration Checksum mismatch for migration 2

Actually there is another solution, but it's a workaround, that should not be done in a properly managed project. However I met a situation, where it was not possible to go down the better road :)

You can update the schame_version table, and actually change the checksum to the new one. This will cause the migration to go through, but can have other side effects.

When deploying to different environments (test, uat, prod, etc) then it might happen, that you have to update the same checksum on more environments. And when it comes to gitflow, and release branches, you can easily mix up the whole.

Default parameters with C++ constructors

Matter of style, but as Matt said, definitely consider marking constructors with default arguments which would allow implicit conversion as 'explicit' to avoid unintended automatic conversion. It's not a requirement (and may not be preferable if you're making a wrapper class which you want to implicitly convert to), but it can prevent errors.

I personally like defaults when appropriate, because I dislike repeated code. YMMV.

Best Practice: Software Versioning

We use a.b.c.d where

  • a - major (incremented on delivery to client)
  • b - minor (incremented on delivery to client)
  • c - revision (incremented on internal releases)
  • d - build (incremented by cruise control)

org.postgresql.util.PSQLException: FATAL: sorry, too many clients already

An explanation of the following error:

org.postgresql.util.PSQLException: FATAL: sorry, too many clients already.


You opened up more than the allowed limit of connections to the database. You ran something like this: Connection conn = myconn.Open(); inside of a loop, and forgot to run conn.close();. Just because your class is destroyed and garbage collected does not release the connection to the database. The quickest fix to this is to make sure you have the following code with whatever class that creates a connection:

protected void finalize() throws Throwable  
    try { your_connection.close(); } 
    catch (SQLException e) { 

Place that code in any class where you create a Connection. Then when your class is garbage collected, your connection will be released.

Run this SQL to see postgresql max connections allowed:

show max_connections;

The default is 100. PostgreSQL on good hardware can support a few hundred connections at a time. If you want to have thousands, you should consider using connection pooling software to reduce the connection overhead.

Take a look at exactly who/what/when/where is holding open your connections:

SELECT * FROM pg_stat_activity;

The number of connections currently used is:

SELECT COUNT(*) from pg_stat_activity;

Debugging strategy

  1. You could give different usernames/passwords to the programs that might not be releasing the connections to find out which one it is, and then look in pg_stat_activity to find out which one is not cleaning up after itself.

  2. Do a full exception stack trace when the connections could not be created and follow the code back up to where you create a new Connection, make sure every code line where you create a connection ends with a connection.close();

How to set the max_connections higher:

max_connections in the postgresql.conf sets the maximum number of concurrent connections to the database server.

  1. First find your postgresql.conf file
  2. If you don't know where it is, query the database with the sql: SHOW config_file;
  3. Mine is in: /var/lib/pgsql/data/postgresql.conf
  4. Login as root and edit that file.
  5. Search for the string: "max_connections".
  6. You'll see a line that says max_connections=100.
  7. Set that number bigger, check the limit for your postgresql version.
  8. Restart the postgresql database for the changes to take effect.

What's the maximum max_connections?

Use this query:

select min_val, max_val from pg_settings where name='max_connections';

I get the value 8388607, in theory that's the most you are allowed to have, but then a runaway process can eat up thousands of connections, and surprise, your database is unresponsive until reboot. If you had a sensible max_connections like 100. The offending program would be denied a new connection.

Can't connect to local MySQL server through socket '/var/mysql/mysql.sock' (38)

If anyone looking for Intialization error

Can't connect to database "/var/run/mysql/mysql.sock"

When running civicrm & drupal just make below changes in

settings.php and civicrm.settings.php

only in places where you try to establish db connection

localhost to #local installation

Using CSS how to change only the 2nd column of a table

Try this:

.countTable table tr td:first-child + td

You could also reiterate in order to style the others columns:

.countTable table tr td:first-child + td + td {...} /* third column */
.countTable table tr td:first-child + td + td + td {...} /* fourth column */
.countTable table tr td:first-child + td + td + td +td {...} /* fifth column */

Remove trailing comma from comma-separated string

public static String removeExtraCommas(String entry) {
        return null;

    String ret="";
    String arr[]=entry.split(",");
    boolean start=true;
    for(String str:arr) {
        if(!"".equalsIgnoreCase(str)) {
            if(start) {
            else {
    return ret;


Access denied for user 'root'@'localhost' with PHPMyAdmin

Edit your phpmyadmin file and if you have Password, insert that in front of Password in following code:

$cfg['Servers'][$i]['verbose'] = 'localhost';
$cfg['Servers'][$i]['host'] = 'localhost';
$cfg['Servers'][$i]['port'] = '3306';
$cfg['Servers'][$i]['socket'] = '';
$cfg['Servers'][$i]['connect_type'] = 'tcp';
$cfg['Servers'][$i]['extension'] = 'mysqli';
$cfg['Servers'][$i]['auth_type'] = 'config';
$cfg['Servers'][$i]['user'] = '**your-root-username**';
$cfg['Servers'][$i]['password'] = '**root-password**';
$cfg['Servers'][$i]['AllowNoPassword'] = true;

How to programmatically close a JFrame

If you have done this to make sure the user can't close the window:


Then you should change your pullThePlug() method to be

public void pullThePlug() {
    // this will make sure WindowListener.windowClosing() et al. will be called.
    WindowEvent wev = new WindowEvent(this, WindowEvent.WINDOW_CLOSING);

    // this will hide and dispose the frame, so that the application quits by
    // itself if there is nothing else around. 
    // if you have other similar frames around, you should dispose them, too.

    // finally, call this to really exit. 
    // i/o libraries such as WiiRemoteJ need this. 
    // also, this is what swing does for JFrame.EXIT_ON_CLOSE

I found this to be the only way that plays nice with the WindowListener and JFrame.DO_NOTHING_ON_CLOSE.

How to determine the content size of a UIWebView?

Also in iOS 7 for proper working of all of mentioned methods add this in your view controller viewDidLoad method:

if ([self respondsToSelector:@selector(automaticallyAdjustsScrollViewInsets)]) {
    self.automaticallyAdjustsScrollViewInsets = NO;

Otherwise neither of methods would work as it should.

how to run vibrate continuously in iphone?

The above answers are good and you can do it in a simple way also.

You can use the recursive method calls.

func vibrateTheDeviceContinuously() throws {
        // Added concurrent queue for next & Vibrate device .utility).async {
            //Vibrate the device

            self.incrementalCount += 1
            usleep(800000) // if you don't want, remove this line.

            do {
                if let isKeepBuzzing = self.iShouldKeepBuzzing , isKeepBuzzing == true {
                    try self.vibrateTheDeviceContinuously()
                 else {
            } catch  {
                //Exception handle

To stop the device vibration use the following line.

self.iShouldKeepBuzzing = false

How can I use onItemSelected in Android?

Joseph: spinner.setOnItemSelectedListener(this) should be below Spinner firstSpinner = (Spinner) findViewById(; on onCreate

Parse error: syntax error, unexpected T_ECHO in

Missing ; after var_dump($row)

How can I determine if a date is between two dates in Java?

Here's a couple ways to do this using the Joda-Time 2.3 library.

One way is to use the simple isBefore and isAfter methods on DateTime instances. By the way, DateTime in Joda-Time is similar in concept to a java.util.Date (a moment in time on the timeline of the Universe) but includes a time zone.

Another way is to build an Interval in Joda-Time. The contains method tests if a given DateTime occurs within the span of time covered by the Interval. The beginning of the Interval is inclusive, but the endpoint is exclusive. This approach is known as "Half-Open", symbolically [).

See both ways in the following code example.

Convert the java.util.Date instances to Joda-Time DateTime instances. Simply pass the Date instance to constructor of DateTime. In practice you should also pass a specific DateTimeZone object rather than rely on JVM’s default time zone.

DateTime dateTime1 = new DateTime( new java.util.Date() ).minusWeeks( 1 );
DateTime dateTime2 = new DateTime( new java.util.Date() );
DateTime dateTime3 = new DateTime( new java.util.Date() ).plusWeeks( 1 );

Compare by testing for before/after…

boolean is1After2 = dateTime1.isAfter( dateTime2 );
boolean is2Before3 = dateTime2.isBefore( dateTime3 );

boolean is2Between1And3 = ( ( dateTime2.isAfter( dateTime1 ) ) && ( dateTime2.isBefore( dateTime3 ) ) );

Using the Interval approach instead of isAfter/isBefore…

Interval interval = new Interval( dateTime1, dateTime3 );
boolean intervalContainsDateTime2 = interval.contains( dateTime2 );

Dump to console…

System.out.println( "DateTimes: " + dateTime1 + " " + dateTime1 + " " + dateTime1 );
System.out.println( "is1After2 " + is1After2 );
System.out.println( "is2Before3 " + is2Before3 );
System.out.println( "is2Between1And3 " + is2Between1And3 );
System.out.println( "intervalContainsDateTime2 " + intervalContainsDateTime2 );

When run…

DateTimes: 2014-01-22T20:26:14.955-08:00 2014-01-22T20:26:14.955-08:00 2014-01-22T20:26:14.955-08:00
is1After2 false
is2Before3 true
is2Between1And3 true
intervalContainsDateTime2 true

ssl_error_rx_record_too_long and Apache SSL

The link mentioned by Subimage was right on the money for me. It suggested changing the virtual host tag, ie, from <VirtualHost> to <VirtualHost _default_:443>

Error code: ssl_error_rx_record_too_long

This usually means the implementation of SSL on your server is not correct. The error is usually caused by a server side problem which the server administrator will need to investigate.

Below are some things we recommend trying.

  • Ensure that port 443 is open and enabled on your server. This is the standard port for https communications.

  • If SSL is using a non-standard port then FireFox 3 can sometimes give this error. Ensure SSL is running on port 443.

  • If using Apache2 check that you are using port 443 for SSL. This can be done by setting the ports.conf file as follows

    Listen 80
    Listen 443 https
  • Make sure you do not have more than one SSL certificate sharing the same IP. Please ensure that all SSL certificates utilise their own dedicated IP.

  • If using Apache2 check your vhost config. Some users have reported changing <VirtualHost> to _default_ resolved the error.

That fixed my problem. It's rare that I google an error message and get the first hit with the right answer! :-)

In addition to the above, these are some other solutions that other folks have found were causing the issue:

  • Make sure that your SSL certificate is not expired

  • Try to specify the Cipher:


RegExp matching string not starting with my


(?!expression) is a negative lookahead; it matches a position where expression doesn't match starting at that position.

SimpleDateFormat and locale based format string

Localization of date string:

Based on redsonic's post:

private String localizeDate(String inputdate, Locale locale) { 

    Date date = new Date();
    SimpleDateFormat dateFormatCN = new SimpleDateFormat("dd-MMM-yyyy", locale);       
    SimpleDateFormat dateFormat = new SimpleDateFormat("dd-MMM-yyyy");

    try {
        date = dateFormat.parse(inputdate);
    } catch (ParseException e) {
        log.warn("Input date was not correct. Can not localize it.");
        return inputdate;
    return dateFormatCN.format(date);

String localizedDate = localizeDate("05-Sep-2013", new Locale("zh","CN"));

will be like 05-??-2013

Call PowerShell script PS1 from another PS1 script inside Powershell ISE

This is just additional info to answers in order to pass argument into the another file

Where you expect argument


    [Parameter( Mandatory = $true)]
    $printName = "Joe"    

Write-Host $printName

How to call the file

    [Parameter( Mandatory = $false)]
    $name = "Joe"    

& ((Split-Path $MyInvocation.InvocationName) + "\PrintName.ps1") -printName $name

If you do not do not provide any input it will default to "Joe" and this will be passed as argument into printName argument in PrintName.ps1 file which will in turn print out the "Joe" string

Programmatically Creating UILabel

In Swift -

var label:UILabel = UILabel(frame: CGRectMake(0, 0, 70, 20)) = CGPointMake(50, 70)
label.textAlignment = NSTextAlignment.Center
label.text = "message"
label.textColor = UIColor.blackColor()

C# Validating input for textbox on winforms


There are many ways to validate your TextBox. You can do this on every keystroke, at a later time, or on the Validating event.

The Validating event gets fired if your TextBox looses focus. When the user clicks on a other Control, for example. If your set e.Cancel = true the TextBox doesn't lose the focus.

MSDN - Control.Validating Event When you change the focus by using the keyboard (TAB, SHIFT+TAB, and so on), by calling the Select or SelectNextControl methods, or by setting the ContainerControl.ActiveControl property to the current form, focus events occur in the following order







When you change the focus by using the mouse or by calling the Focus method, focus events occur in the following order:







Sample Validating Event

private void textBox1_Validating(object sender, CancelEventArgs e)
    if (textBox1.Text != "something")
        e.Cancel = true;


You can use the ErrorProvider to visualize that your TextBox is not valid. Check out Using Error Provider Control in Windows Forms and C#

More Information

Merge some list items in a Python List

That example is pretty vague, but maybe something like this?

items = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h']
items[3:6] = [''.join(items[3:6])]

It basically does a splice (or assignment to a slice) operation. It removes items 3 to 6 and inserts a new list in their place (in this case a list with one item, which is the concatenation of the three items that were removed.)

For any type of list, you could do this (using the + operator on all items no matter what their type is):

items = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h']
items[3:6] = [reduce(lambda x, y: x + y, items[3:6])]

This makes use of the reduce function with a lambda function that basically adds the items together using the + operator.

How to ignore the certificate check when ssl

Mention has been made that before .NET 4.5 the property on the request to access its ServicePointManager was not available.

Here is .NET 4.0 code that will give you access to the ServicePoint on a per-request basis. It doesn't give you access to the per-request callback, but it should let you find out more details about the problem. Just access the scvPoint.Certificate (or ClientCertificate if you prefer) properties.

WebRequest request = WebRequest.Create(uri);

// oddity: these two .Address values are not necessarily the same!
//  The service point appears to be related to the .Host, not the Uri itself.
//  So, check the .Host vlaues before fussing in the debugger.
ServicePoint svcPoint = ServicePointManager.FindServicePoint(uri);
if (null != svcPoint)
    if (!request.RequestUri.Host.Equals(svcPoint.Address.Host, StringComparison.OrdinalIgnoreCase))
        Debug.WriteLine(".Address              == " + request.RequestUri.ToString());
        Debug.WriteLine(".ServicePoint.Address == " + svcPoint.Address.ToString());
    Debug.WriteLine(".IssuerName           == " + svcPoint.Certificate.GetIssuerName());

Adjust UILabel height to text

The solution suggested by Anorak as a computed property in an extension for UILabel:

extension UILabel
var optimalHeight : CGFloat
            let label = UILabel(frame: CGRectMake(0, 0, self.frame.width, CGFloat.max))
            label.numberOfLines = 0
            label.lineBreakMode = self.lineBreakMode
            label.font = self.font
            label.text = self.text


            return label.frame.height


self.brandModelLabel.frame.size.height = self.brandModelLabel.optimalHeight

Is there an auto increment in sqlite?

I know this answer is a bit late.
My purpose for this answer is for everyone's reference should they encounter this type of challenge with SQLite now or in the future and they're having a hard time with it.

Now, looking back at your query, it should be something like this.

CREATE TABLE people (id integer primary key autoincrement, first_name varchar(20), last_name varchar(20));

It works on my end. Like so,

enter image description here

Just in case you are working with SQLite, I suggest for you to check out DB Browser for SQLite. Works on different platforms as well.

Can I remove the URL from my print css, so the web address doesn't print?

The headers and footers for printing from browsers is, sadly, a browser preference, not a document-level element that you can style. Refer to my very similar question for further workarounds and disappointment.

How to return multiple objects from a Java method?

In C++ (STL) there is a pair class for bundling two objects. In Java Generics a pair class isn't available, although there is some demand for it. You could easily implement it yourself though.

I agree however with some other answers that if you need to return two or more objects from a method, it would be better to encapsulate them in a class.

How to parse a JSON string to an array using Jackson

I finally got it:

ObjectMapper objectMapper = new ObjectMapper();
TypeFactory typeFactory = objectMapper.getTypeFactory();
List<SomeClass> someClassList = objectMapper.readValue(jsonString, typeFactory.constructCollectionType(List.class, SomeClass.class));

How/When does Execute Shell mark a build as failure in Jenkins?

Simple and short answer to your question is

Please add following line into your "Execute shell" Build step.


Now let me explain you the reason why we require this line for "Execute Shell" build job.

By default Jenkins take /bin/sh -xe and this means -x will print each and every command.And the other option -e, which causes shell to stop running a script immediately when any command exits with non-zero (when any command fails) exit code.

So by adding the #!/bin/sh will allow you to execute with no option.

Return rows in random order

The usual method is to use the NEWID() function, which generates a unique GUID. So,


Pandas: ValueError: cannot convert float NaN to integer

For identifying NaN values use boolean indexing:


Then for removing all non-numeric values use to_numeric with parameter errors='coerce' - to replace non-numeric values to NaNs:

df['x'] = pd.to_numeric(df['x'], errors='coerce')

And for remove all rows with NaNs in column x use dropna:

df = df.dropna(subset=['x'])

Last convert values to ints:

df['x'] = df['x'].astype(int)

Spaces in URLs?

Spaces are simply replaced by "%20" like :

How to convert a Datetime string to a current culture datetime string

This works for me:

string myTime = DateTime.Parse("12/1/2011")

Remove grid, background color, and top and right borders from ggplot2

The above options do not work for maps created with sf and geom_sf(). Hence, I want to add the relevant ndiscr parameter here. This will create a nice clean map showing only the features.


ggplot() + 
  geom_sf(data = some_shp) + 
  theme_minimal() +                     # white background
  theme(axis.text = element_blank(),    # remove geographic coordinates
        axis.ticks = element_blank()) + # remove ticks
  coord_sf(ndiscr = 0)                  # remove grid in the background

Convert JSONArray to String Array

Was trying one of the same scenario but found one different and simple solution to convert JSONArray into List.

import java.lang.reflect.Type;

String jsonStringArray = "[\"JSON\",\"To\",\"Java\"]";                 
//creating Gson instance to convert JSON array to Java array
    Gson converter = new Gson();                  
    Type type = new TypeToken<List<String>>(){}.getType();
    List<String> list =  converter.fromJson(jsonStringArray, type );

Give a try

jQuery - get all divs inside a div with class ".container"

To set the class when clicking on a div immediately within the .container element, you could use:

$('.container>div').click(function () {

How do I call the base class constructor?

In the header file define a base class:

class BaseClass {

Then define a derived class as inheriting the BaseClass:

class DerivedClass : public BaseClass {

In the source file define the BaseClass constructor:

     //Perform BaseClass initialization

By default the derived constructor only calls the default base constructor with no parameters; so in this example, the base class constructor is NOT called automatically when the derived constructor is called, but it can be achieved simply by adding the base class constructor syntax after a colon (:). Define a derived constructor that automatically calls its base constructor:

DerivedClass::DerivedClass(params) : BaseClass(params)
     //This occurs AFTER BaseClass(params) is called first and can
     //perform additional initialization for the derived class

The BaseClass constructor is called BEFORE the DerivedClass constructor, and the same/different parameters params may be forwarded to the base class if desired. This can be nested for deeper derived classes. The derived constructor must call EXACTLY ONE base constructor. The destructors are AUTOMATICALLY called in the REVERSE order that the constructors were called.

EDIT: There is an exception to this rule if you are inheriting from any virtual classes, typically to achieve multiple inheritance or diamond inheritance. Then you MUST explicitly call the base constructors of all virtual base classes and pass the parameters explicitly, otherwise it will only call their default constructors without any parameters. See: virtual inheritance - skipping constructors

How to reload a page after the OK click on the Alert Page

Use javascript confirm() method instead of alert. It returns true if the user clicked ok button and returns false when user clicked on cancel button. Sample code will look like this :

if(confirm('Successful Message')){

How to check if a variable exists in a FreeMarker template?

To check if the value exists:

[#if userName??]
   Hi ${userName}, How are you?

Or with the standard freemarker syntax:

<#if userName??>
   Hi ${userName}, How are you?

To check if the value exists and is not empty:

<#if userName?has_content>
    Hi ${userName}, How are you?

How to delete an element from a Slice in Golang

The best way to do it is to use the append function:

package main

import (

func main() {
    x := []int{4, 5, 6, 7, 88}
    x = append(x[:2], x[4:]...)//deletes 6 and 7

What are the differences between type() and isinstance()?

For the real differences, we can find it in code, but I can't find the implement of the default behavior of the isinstance().

However we can get the similar one abc.__instancecheck__ according to __instancecheck__.

From above abc.__instancecheck__, after using test below:

# file tree
# /test/
# /test/aaa/
# /test/aaa/
class b():

# /test/aaa/
import sys

from aaa.aa import b
from aa import b as c

d = b()

print(b, c, d.__class__)
for i in [b, c, object]:
    print(i, '__subclasses__',  i.__subclasses__())
    print(i, '__mro__', i.__mro__)
    print(i, '__subclasshook__', i.__subclasshook__(d.__class__))
    print(i, '__subclasshook__', i.__subclasshook__(type(d)))
print(isinstance(d, b))
print(isinstance(d, c))

<class 'aaa.aa.b'> <class 'aa.b'> <class 'aaa.aa.b'>
<class 'aaa.aa.b'> __subclasses__ []
<class 'aaa.aa.b'> __mro__ (<class 'aaa.aa.b'>, <class 'object'>)
<class 'aaa.aa.b'> __subclasshook__ NotImplemented
<class 'aaa.aa.b'> __subclasshook__ NotImplemented
<class 'aa.b'> __subclasses__ []
<class 'aa.b'> __mro__ (<class 'aa.b'>, <class 'object'>)
<class 'aa.b'> __subclasshook__ NotImplemented
<class 'aa.b'> __subclasshook__ NotImplemented
<class 'object'> __subclasses__ [..., <class 'aaa.aa.b'>, <class 'aa.b'>]
<class 'object'> __mro__ (<class 'object'>,)
<class 'object'> __subclasshook__ NotImplemented
<class 'object'> __subclasshook__ NotImplemented

I get this conclusion, For type:

# according to `abc.__instancecheck__`, they are maybe different! I have not found negative one 
type(INSTANCE) ~= INSTANCE.__class__
type(CLASS) ~= CLASS.__class__

For isinstance:

# guess from `abc.__instancecheck__`
return any(c in cls.__mro__ or c in cls.__subclasses__ or cls.__subclasshook__(c) for c in {INSTANCE.__class__, type(INSTANCE)})

BTW: better not to mix use relative and absolutely import, use absolutely import from project_dir( added by sys.path)

How do I merge changes to a single file, rather than merging commits?

I came across the same problem. To be precise, I have two branches A and B with the same files but a different programming interface in some files. Now the methods of file f, which is independent of the interface differences in the two branches, were changed in branch B, but the change is important for both branches. Thus, I need to merge just file f of branch B into file f of branch A.

A simple command already solved the problem for me if I assume that all changes are committed in both branches A and B:

git checkout A

git checkout --patch B f

The first command switches into branch A, into where I want to merge B's version of the file f. The second command patches the file f with f of HEAD of B. You may even accept/discard single parts of the patch. Instead of B you can specify any commit here, it does not have to be HEAD.

Community edit: If the file f on B does not exist on A yet, then omit the --patch option. Otherwise, you'll get a "No Change." message.

Difference between "include" and "require" in php

You find the differences explained in the detailed PHP manual on the page of require:

require is identical to include except upon failure it will also produce a fatal E_COMPILE_ERROR level error. In other words, it will halt the script whereas include only emits a warning (E_WARNING) which allows the script to continue.

See @efritz's answer for an example

JavaFX Location is not set error message

I think problem is either incorrect layout name or invalid layout file path.

for IntelliJ, you can create resource directory and place layout files there.

FXMLLoader loader = new FXMLLoader();
rootLayout = loader.load();

Can I multiply strings in Java to repeat sequences?

we can create multiply strings using * in python but not in java you can use for loop in your case:

String sample="123";
for(int i=0;i<3;i++)

Proper use of 'yield return'

I tend to use yield-return when I calculate the next item in the list (or even the next group of items).

Using your Version 2, you must have the complete list before returning. By using yield-return, you really only need to have the next item before returning.

Among other things, this helps spread the computational cost of complex calculations over a larger time-frame. For example, if the list is hooked up to a GUI and the user never goes to the last page, you never calculate the final items in the list.

Another case where yield-return is preferable is if the IEnumerable represents an infinite set. Consider the list of Prime Numbers, or an infinite list of random numbers. You can never return the full IEnumerable at once, so you use yield-return to return the list incrementally.

In your particular example, you have the full list of products, so I'd use Version 2.

Query to list all users of a certain group

And the more complex query if you need to search in a several groups:

(&(objectCategory=user)(|(memberOf=CN=GroupOne,OU=Security Groups,OU=Groups,DC=example,DC=com)(memberOf=CN=GroupTwo,OU=Security Groups,OU=Groups,DC=example,DC=com)(memberOf=CN=GroupThree,OU=Security Groups,OU=Groups,DC=example,DC=com)))

The same example with recursion:

(&(objectCategory=user)(|(memberOf:1.2.840.113556.1.4.1941:=CN=GroupOne,OU=Security Groups,OU=Groups,DC=example,DC=com)(memberOf:1.2.840.113556.1.4.1941:=CN=GroupTwo,OU=Security Groups,OU=Groups,DC=example,DC=com)(memberOf:1.2.840.113556.1.4.1941:=CN=GroupThree,OU=Security Groups,OU=Groups,DC=example,DC=com)))

How to set cornerRadius for only top-left and top-right corner of a UIView?

Here is a short method implemented like this:

- (void)viewDidLoad {
    [super viewDidLoad];
    UIButton *openInMaps = [UIButton new];
    [openInMaps setFrame:CGRectMake(15, 135, 114, 70)];
    openInMaps = (UIButton *)[self roundCornersOnView:openInMaps onTopLeft:NO topRight:NO bottomLeft:YES bottomRight:NO radius:5.0];

- (UIView *)roundCornersOnView:(UIView *)view onTopLeft:(BOOL)tl topRight:(BOOL)tr bottomLeft:(BOOL)bl bottomRight:(BOOL)br radius:(float)radius {

    if (tl || tr || bl || br) {
        UIRectCorner corner = 0;
        if (tl) {corner = corner | UIRectCornerTopLeft;}
        if (tr) {corner = corner | UIRectCornerTopRight;}
        if (bl) {corner = corner | UIRectCornerBottomLeft;}
        if (br) {corner = corner | UIRectCornerBottomRight;}

        UIView *roundedView = view;
        UIBezierPath *maskPath = [UIBezierPath bezierPathWithRoundedRect:roundedView.bounds byRoundingCorners:corner cornerRadii:CGSizeMake(radius, radius)];
        CAShapeLayer *maskLayer = [CAShapeLayer layer];
        maskLayer.frame = roundedView.bounds;
        maskLayer.path = maskPath.CGPath;
        roundedView.layer.mask = maskLayer;
        return roundedView;
    return view;

C++ Erase vector element by value rather than by position?

You can not do that directly. You need to use std::remove algorithm to move the element to be erased to the end of the vector and then use erase function. Something like: myVector.erase(std::remove(myVector.begin(), myVector.end(), 8), myVec.end());. See this erasing elements from vector for more details.

Escaping special characters in Java Regular Expressions

I wrote this pattern:

Pattern SPECIAL_REGEX_CHARS = Pattern.compile("[{}()\\[\\].+*?^$\\\\|]");

And use it in this method:

String escapeSpecialRegexChars(String str) {

    return SPECIAL_REGEX_CHARS.matcher(str).replaceAll("\\\\$0");

Then you can use it like this, for example:

Pattern toSafePattern(String text)
    return Pattern.compile(".*" + escapeSpecialRegexChars(text) + ".*");

We needed to do that because, after escaping, we add some regex expressions. If not, you can simply use \Q and \E:

Pattern toSafePattern(String text)
    return Pattern.compile(".*\\Q" + text + "\\E.*")

enable or disable checkbox in html

The HTML parser simply doesn't interpret the inlined javascript like this.

You may do this :

<td><input type="checkbox" id="repriseCheckBox" name="repriseCheckBox"/></td>

<script>document.getElementById("repriseCheckBox").disabled=checkStat == 1 ? true : false;</script>

rand() between 0 and 1

In my case (I'm using VS 2017) works fine the following simple code:

#include "pch.h"
#include <iostream>
#include <stdlib.h>
#include <time.h>

int main()

    for (int i = 1000; i > 0; i--) //try it thousand times
        int randnum = (double)rand() / ((double)RAND_MAX + 1);
        std::cout << " rnum: " << rand()%2 ;

Iterating over every two elements in a list

The title of this question is misleading, you seem to be looking for consecutive pairs, but if you want to iterate over the set of all possible pairs than this will work :

for i,v in enumerate(items[:-1]):
        for u in items[i+1:]:

Calling Javascript function from server side

You can call the function from code behind like this :


protected void MyButton_Click(object sender, EventArgs e)
    Page.ClientScript.RegisterStartupScript(this.GetType(), "myScript", "AnotherFunction();", true);


<html xmlns="">
<head id="Head1" runat="server">
<title>My Page</title>
<script src="" type="text/javascript"></script>
<script type="text/javascript">
    function Test() {
    function AnotherFunction()
        alert("This is another function");
<form id="form2" runat="server">
            <asp:RadioButtonList ID="SearchCategory" runat="server" onchange="Test()"  RepeatDirection="Horizontal"  BorderStyle="Solid">
    <tr id="ButtonRow"style="display:none">
            <asp:Button ID="MyButton" runat="server" Text="Click Here" OnClick="MyButton_Click" />

ParseError: not well-formed (invalid token) using cElementTree

The only thing that worked for me is I had to add mode and encoding while opening the file like below:

with open(filenames[0], mode='r',encoding='utf-8') as f:

Otherwise it was failing every time with invalid token error if I simply do this:

 f = open(filenames[0], 'r')

push() a two-dimensional array

You have some errors in your code:

  1. Use myArray[i].push( 0 ); to add a new column. Your code (myArray[i][j].push(0);) would work in a 3-dimensional array as it tries to add another element to an array at position [i][j].
  2. You only expand (col-d)-many columns in all rows, even in those, which haven't been initialized yet and thus have no entries so far.

One correct, although kind of verbose version, would be the following:

var r = 3; //start from rows 3

var rows = 8;
var cols = 7;

// expand to have the correct amount or rows
for( var i=r; i<rows; i++ ) {
  myArray.push( [] );

// expand all rows to have the correct amount of cols
for (var i = 0; i < rows; i++)
    for (var j =  myArray[i].length; j < cols; j++)

Extract the first (or last) n characters of a string

Make it simple and use R basic functions:

# To get the LEFT part:
> substr(a, 1, 4)
[1] "left"
# To get the MIDDLE part:
> substr(a, 3, 7)
[1] "ftrig"
# To get the RIGHT part:
> substr(a, 5, 10)
[1] "right"

The substr() function tells you where start and stop substr(x, start, stop)

How many threads is too many?

Some people would say that two threads is too many - I'm not quite in that camp :-)

Here's my advice: measure, don't guess. One suggestion is to make it configurable and initially set it to 100, then release your software to the wild and monitor what happens.

If your thread usage peaks at 3, then 100 is too much. If it remains at 100 for most of the day, bump it up to 200 and see what happens.

You could actually have your code itself monitor usage and adjust the configuration for the next time it starts but that's probably overkill.

For clarification and elaboration:

I'm not advocating rolling your own thread pooling subsystem, by all means use the one you have. But, since you were asking about a good cut-off point for threads, I assume your thread pool implementation has the ability to limit the maximum number of threads created (which is a good thing).

I've written thread and database connection pooling code and they have the following features (which I believe are essential for performance):

  • a minimum number of active threads.
  • a maximum number of threads.
  • shutting down threads that haven't been used for a while.

The first sets a baseline for minimum performance in terms of the thread pool client (this number of threads is always available for use). The second sets a restriction on resource usage by active threads. The third returns you to the baseline in quiet times so as to minimise resource use.

You need to balance the resource usage of having unused threads (A) against the resource usage of not having enough threads to do the work (B).

(A) is generally memory usage (stacks and so on) since a thread doing no work will not be using much of the CPU. (B) will generally be a delay in the processing of requests as they arrive as you need to wait for a thread to become available.

That's why you measure. As you state, the vast majority of your threads will be waiting for a response from the database so they won't be running. There are two factors that affect how many threads you should allow for.

The first is the number of DB connections available. This may be a hard limit unless you can increase it at the DBMS - I'm going to assume your DBMS can take an unlimited number of connections in this case (although you should ideally be measuring that as well).

Then, the number of threads you should have depend on your historical use. The minimum you should have running is the minimum number that you've ever had running + A%, with an absolute minimum of (for example, and make it configurable just like A) 5.

The maximum number of threads should be your historical maximum + B%.

You should also be monitoring for behaviour changes. If, for some reason, your usage goes to 100% of available for a significant time (so that it would affect the performance of clients), you should bump up the maximum allowed until it's once again B% higher.

In response to the "what exactly should I measure?" question:

What you should measure specifically is the maximum amount of threads in concurrent use (e.g., waiting on a return from the DB call) under load. Then add a safety factor of 10% for example (emphasised, since other posters seem to take my examples as fixed recommendations).

In addition, this should be done in the production environment for tuning. It's okay to get an estimate beforehand but you never know what production will throw your way (which is why all these things should be configurable at runtime). This is to catch a situation such as unexpected doubling of the client calls coming in.

Best /Fastest way to read an Excel Sheet into a DataTable?

The below code is tested by myself and is very simple, understandable, usable and fast. This code, initially takes all sheet names, then puts all tables of that excel file in a DataSet.

    public static DataSet ToDataSet(string exceladdress, int startRecord = 0, int maxRecord = -1, string condition = "")
        DataSet result = new DataSet();
        using (OleDbConnection connection = new OleDbConnection(
                ? "Provider=Microsoft.ACE.OLEDB.12.0;Data Source='" + exceladdress + "';" + "Extended Properties='Excel 12.0 Xml;HDR=YES;'"
                : "provider=Microsoft.Jet.OLEDB.4.0;Data Source='" + exceladdress + "';Extended Properties=Excel 8.0;"))
                DataTable schema = connection.GetOleDbSchemaTable(OleDbSchemaGuid.Tables, null);
                foreach (DataRow drSheet in schema.Rows)
                    if (drSheet["TABLE_NAME"].ToString().Contains("$"))
                        string s = drSheet["TABLE_NAME"].ToString();
                        if (s.StartsWith("'")) s = s.Substring(1, s.Length - 2);
                        System.Data.OleDb.OleDbDataAdapter command =
                            new System.Data.OleDb.OleDbDataAdapter(string.Join("", "SELECT * FROM [", s, "] ", condition), connection);
                        DataTable dt = new DataTable();
                        if (maxRecord > -1 && startRecord > -1) command.Fill(startRecord, maxRecord, dt);
                        else command.Fill(dt);
                return result;
            catch (Exception ex) { return null; }
            finally { connection.Close(); }


How to make layout with rounded corners..?

I think a better way to do it is to merge 2 things:

  1. make a bitmap of the layout, as shown here.

  2. make a rounded drawable from the bitmap, as shown here

  3. set the drawable on an imageView.

This will handle cases that other solutions have failed to solve, such as having content that has corners.

I think it's also a bit more GPU-friendly, as it shows a single layer instead of 2 .

The only better way is to make a totally customized view, but that's a lot of code and might take a lot of time. I think that what I suggested here is the best of both worlds.

Here's a snippet of how it can be done:

 * shows a bitmap as if it had rounded corners. based on :
 * easy alternative from support library: RoundedBitmapDrawableFactory.create( ...) ; 
public class RoundedCornersDrawable extends BitmapDrawable {

    private final BitmapShader bitmapShader;
    private final Paint p;
    private final RectF rect;
    private final float borderRadius;

    public RoundedCornersDrawable(final Resources resources, final Bitmap bitmap, final float borderRadius) {
        super(resources, bitmap);
        bitmapShader = new BitmapShader(getBitmap(), Shader.TileMode.CLAMP, Shader.TileMode.CLAMP);
        final Bitmap b = getBitmap();
        p = getPaint();
        final int w = b.getWidth(), h = b.getHeight();
        rect = new RectF(0, 0, w, h);
        this.borderRadius = borderRadius < 0 ? 0.15f * Math.min(w, h) : borderRadius;

    public void draw(final Canvas canvas) {
        canvas.drawRoundRect(rect, borderRadius, borderRadius, p);

public class CustomView extends ImageView {
    private View mMainContainer;
    private boolean mIsDirty=false;

    // TODO for each change of views/content, set mIsDirty to true and call invalidate

    protected void onDraw(final Canvas canvas) {
        if (mIsDirty) {
            mIsDirty = false;

     * draws the view's content to a bitmap. code based on :
    public static Bitmap drawToBitmap(final View viewToDrawFrom, final int width, final int height) {
        // Create a new bitmap and a new canvas using that bitmap
        final Bitmap bmp = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
        final Canvas canvas = new Canvas(bmp);
        // Supply measurements
        viewToDrawFrom.measure(MeasureSpec.makeMeasureSpec(canvas.getWidth(), MeasureSpec.EXACTLY),
                MeasureSpec.makeMeasureSpec(canvas.getHeight(), MeasureSpec.EXACTLY));
        // Apply the measures so the layout would resize before drawing.
        viewToDrawFrom.layout(0, 0, viewToDrawFrom.getMeasuredWidth(), viewToDrawFrom.getMeasuredHeight());
        // and now the bmp object will actually contain the requested layout
        canvas.drawBitmap(viewToDrawFrom.getDrawingCache(), 0, 0, new Paint());
        return bmp;

    private void drawContent() {
        if (getMeasuredWidth() <= 0 || getMeasuredHeight() <= 0)
        final Bitmap bitmap = drawToBitmap(mMainContainer, getMeasuredWidth(), getMeasuredHeight());
        final RoundedCornersDrawable drawable = new RoundedCornersDrawable(getResources(), bitmap, 15);


EDIT: found a nice alternative, based on "RoundKornersLayouts" library. Have a class that will be used for all of the layout classes you wish to extend, to be rounded:

//based on
class CanvasRounder(cornerRadius: Float, cornerStrokeColor: Int = 0, cornerStrokeWidth: Float = 0F) {
    private val path =
    private lateinit var rectF: RectF
    private var strokePaint: Paint?
    var cornerRadius: Float = cornerRadius
        set(value) {
            field = value

    init {
        if (cornerStrokeWidth <= 0)
            strokePaint = null
        else {
            strokePaint = Paint()
            strokePaint!!.style = Paint.Style.STROKE
            strokePaint!!.isAntiAlias = true
            strokePaint!!.color = cornerStrokeColor
            strokePaint!!.strokeWidth = cornerStrokeWidth

    fun round(canvas: Canvas, drawFunction: (Canvas) -> Unit) {
        val save =
        if (strokePaint != null)
            canvas.drawRoundRect(rectF, cornerRadius, cornerRadius, strokePaint)

    fun updateSize(currentWidth: Int, currentHeight: Int) {
        rectF =, 0f, currentWidth.toFloat(), currentHeight.toFloat())

    private fun resetPath() {
        path.addRoundRect(rectF, cornerRadius, cornerRadius, Path.Direction.CW)


Then, in each of your customized layout classes, add code similar to this one:

class RoundedConstraintLayout : ConstraintLayout {
    private lateinit var canvasRounder: CanvasRounder

    constructor(context: Context) : super(context) {
        init(context, null, 0)

    constructor(context: Context, attrs: AttributeSet) : super(context, attrs) {
        init(context, attrs, 0)

    constructor(context: Context, attrs: AttributeSet, defStyle: Int) : super(context, attrs, defStyle) {
        init(context, attrs, defStyle)

    private fun init(context: Context, attrs: AttributeSet?, defStyle: Int) {
        val array = context.obtainStyledAttributes(attrs, R.styleable.RoundedCornersView, 0, 0)
        val cornerRadius = array.getDimension(R.styleable.RoundedCornersView_corner_radius, 0f)
        val cornerStrokeColor = array.getColor(R.styleable.RoundedCornersView_corner_stroke_color, 0)
        val cornerStrokeWidth = array.getDimension(R.styleable.RoundedCornersView_corner_stroke_width, 0f)
        canvasRounder = CanvasRounder(cornerRadius,cornerStrokeColor,cornerStrokeWidth)
            setLayerType(FrameLayout.LAYER_TYPE_SOFTWARE, null)

    override fun onSizeChanged(currentWidth: Int, currentHeight: Int, oldWidth: Int, oldheight: Int) {
        super.onSizeChanged(currentWidth, currentHeight, oldWidth, oldheight)
        canvasRounder.updateSize(currentWidth, currentHeight)

    override fun draw(canvas: Canvas) = canvasRounder.round(canvas) { super.draw(canvas) }

    override fun dispatchDraw(canvas: Canvas) = canvasRounder.round(canvas) { super.dispatchDraw(canvas) }


If you wish to support attributes, use this as written on the library:

  <declare-styleable name="RoundedCornersView">
      <attr name="corner_radius" format="dimension"/>
      <attr name="corner_stroke_width" format="dimension"/>
      <attr name="corner_stroke_color" format="color"/>

Another alternative, which might be easier for most uses: use MaterialCardView . It allows customizing the rounded corners, stroke color and width, and elevation.


    xmlns:android="" xmlns:app=""
    xmlns:tools="" android:layout_width="match_parent"
    android:layout_height="match_parent" android:clipChildren="false" android:clipToPadding="false"

        android:layout_width="100dp" android:layout_height="100dp" android:layout_gravity="center"
        app:cardCornerRadius="8dp" app:cardElevation="8dp" app:strokeColor="#f00" app:strokeWidth="2dp">

            android:layout_width="match_parent" android:layout_height="match_parent" android:background="#0f0"/>



And the result:

enter image description here

Do note that there is a slight artifacts issue at the edges of the stroke (leaves some pixels of the content there), if you use it. You can notice it if you zoom in. I've reported about this issue here.

EDIT: seems to be fixed, but not on the IDE. Reported here.

How do I use select with date condition?

Select * from Users where RegistrationDate >= CONVERT(datetime, '01/20/2009', 103)

is safe to use, independent of the date settings on the server.

The full list of styles can be found here.

How to find the Number of CPU Cores via .NET/C#?

The following program prints the logical and physical cores of a windows machine.

#define STRICT
#include "stdafx.h"
#include <windows.h>
#include <stdio.h>
#include <omp.h>

template<typename T>
T *AdvanceBytes(T *p, SIZE_T cb)
 return reinterpret_cast<T*>(reinterpret_cast<BYTE *>(p) + cb);

class EnumLogicalProcessorInformation
 EnumLogicalProcessorInformation(LOGICAL_PROCESSOR_RELATIONSHIP Relationship)
  : m_pinfoBase(nullptr), m_pinfoCurrent(nullptr), m_cbRemaining(0)
  DWORD cb = 0;
  if (GetLogicalProcessorInformationEx(Relationship,
                                       nullptr, &cb)) return;
  if (GetLastError() != ERROR_INSUFFICIENT_BUFFER) return;

  m_pinfoBase =
                                     (LocalAlloc(LMEM_FIXED, cb));
  if (!m_pinfoBase) return;

  if (!GetLogicalProcessorInformationEx(Relationship, 
                                        m_pinfoBase, &cb)) return;

  m_pinfoCurrent = m_pinfoBase;
  m_cbRemaining = cb;

 ~EnumLogicalProcessorInformation() { LocalFree(m_pinfoBase); }

 void MoveNext()
  if (m_pinfoCurrent) {
   m_cbRemaining -= m_pinfoCurrent->Size;
   if (m_cbRemaining) {
    m_pinfoCurrent = AdvanceBytes(m_pinfoCurrent,
   } else {
    m_pinfoCurrent = nullptr;

                                         { return m_pinfoCurrent; }
 DWORD m_cbRemaining;

int __cdecl main(int argc, char **argv)
  int numLogicalCore = 0;
  int numPhysicalCore = 0;

  for (EnumLogicalProcessorInformation enumInfo(RelationProcessorCore);
      auto pinfo = enumInfo.Current(); enumInfo.MoveNext()) 
      int numThreadPerCore = (pinfo->Processor.Flags == LTP_PC_SMT) ? 2 : 1;
      // std::cout << "thread per core: "<< numThreadPerCore << std::endl;
      numLogicalCore += numThreadPerCore;
      numPhysicalCore += 1;

  printf ("Number of physical core = %d , Number of Logical core = %d \n", numPhysicalCore, numLogicalCore );

 char c = getchar(); /* just to wait on to see the results in the command prompt */
 return 0;

I tested with Intel Xeon four cores with hyper threading and here is the result
Number of physical core = 4 , Number of Logical core = 8

HTML: How to center align a form


does work in most cases like The Wobbuffet mentioned above...

Intel's HAXM equivalent for AMD on Windows OS

This limitation (of Windows) should be publicly announced! The issue for me is the combination of the following: Windows 10 + AMD CPU (with AMD-V/SMV) +/- Hyper Visor

I have no issues running: Intel (with VT-x) + Linux or AMD (with AMD-V) + Linux

Link to Android studio issue here:

Xamarin/Visual Studio seems to have a workaround, but I haven't tested it yet:

If you need to use Hyper-V for other emulators then I'd recommend using the Microsoft Android Emulator instead, which uses Hyper-V and can also be used with Xamarin Studio/Visual Studio. You can download it for free from here.

I will update this after I confirm it works. Wish I would have known this before purchasing a new machine.

UPDATE!! It does not work "Requires Intel ..." error message is shown

Final note:

*Must be revision F3 or grater or must be F2 with BIOS support. Presence or absence of SVM Disable or other virtualization options in the bios does not ensure presence of BIOS support. You should contact the OEM to ensure support of Hyper-V.

*Some AMD BIOS's have options to enable/disable SVM (virtualization assistance)

*Some BIOS's list this as SVM Disable and it's a double negative, i.e. you want to disable SVM disable to enable SVM.

*Some BIOS's list this as Secure Virtualization, thus enabling Secure Virtualization will enable SVM

*Must have No-Execute enabled in the BIOS, sometime this is referred to as NX or Execute Disable

*If you want to find CPU's that are F3 see AMD's guide or

Using sed to mass rename files

The easiest way would be:

for i in F00001*; do mv "$i" "${i/F00001/F0001}"; done

or, portably,

for i in F00001*; do mv "$i" "F0001${i#F00001}"; done

This replaces the F00001 prefix in the filenames with F0001. credits to mahesh here:

How to style HTML5 range input to have different color before and after slider?

A small update to this one:

if you use the following it will update on the fly rather than on mouse release.

"change mousemove", function"

$('input[type="range"]').on("change mousemove", function () {
    var val = ($(this).val() - $(this).attr('min')) / ($(this).attr('max') - $(this).attr('min'));

                '-webkit-gradient(linear, left top, right top, '
                + 'color-stop(' + val + ', #2f466b), '
                + 'color-stop(' + val + ', #d3d3db)'
                + ')'

How do I properly clean up Excel interop objects?

So far it seems all answers involve some of these:

  1. Kill the process
  2. Use GC.Collect()
  3. Keep track of every COM object and release it properly.

Which makes me appreciate how difficult this issue is :)

I have been working on a library to simplify access to Excel, and I am trying to make sure that people using it won't leave a mess (fingers crossed).

Instead of writing directly on the interfaces Interop provides, I am making extension methods to make live easier. Like ApplicationHelpers.CreateExcel() or workbook.CreateWorksheet("mySheetNameThatWillBeValidated"). Naturally, anything that is created may lead to an issue later on cleaning up, so I am actually favoring killing the process as last resort. Yet, cleaning up properly (third option), is probably the least destructive and most controlled.

So, in that context I was wondering whether it wouldn't be best to make something like this:

public abstract class ReleaseContainer<T>
    private readonly Action<T> actionOnT;

    protected ReleaseContainer(T releasible, Action<T> actionOnT)
        this.actionOnT = actionOnT;
        this.Releasible = releasible;


    public T Releasible { get; private set; }

    private void Release()
        Releasible = default(T);

I used 'Releasible' to avoid confusion with Disposable. Extending this to IDisposable should be easy though.

An implementation like this:

public class ApplicationContainer : ReleaseContainer<Application>
    public ApplicationContainer()
        : base(new Application(), ActionOnExcel)

    private static void ActionOnExcel(Application application)
        application.Show(); // extension method. want to make sure the app is visible.

And one could do something similar for all sorts of COM objects.

In the factory method:

    public static Application CreateExcelApplication(bool hidden = false)
        var excel = new ApplicationContainer().Releasible;
        excel.Visible = !hidden;

        return excel;

I would expect that every container will be destructed properly by the GC, and therefore automatically make the call to Quit and Marshal.FinalReleaseComObject.

Comments? Or is this an answer to the question of the third kind?

How to make <a href=""> link look like a button?

You have got two options for consistency.

  1. Use framework-specific tags, and use them throughout the website.
  2. Use JavaScript to emulate a link on a button element, and then have the button consistent with browser's buttons look. Those css button-look hacks will never be accurate.


<button onclick="location.href = 'Homepage.html'; return false;">My Button</button>

return false; is to prevent the default behavior of the button being clicked.

Check if String / Record exists in DataTable

Something like this

 string find = "item_manuf_id = 'some value'";
 DataRow[] foundRows = table.Select(find);

Spark - SELECT WHERE or filtering?

As Yaron mentioned, there isn't any difference between where and filter.

filter is an overloaded method that takes a column or string argument. The performance is the same, regardless of the syntax you use.

filter overloaded method

We can use explain() to see that all the different filtering syntaxes generate the same Physical Plan. Suppose you have a dataset with person_name and person_country columns. All of the following code snippets will return the same Physical Plan below:

df.where("person_country = 'Cuba'").explain()
df.where($"person_country" === "Cuba").explain()
df.where('person_country === "Cuba").explain()
df.filter("person_country = 'Cuba'").explain()

These all return this Physical Plan:

== Physical Plan ==
*(1) Project [person_name#152, person_country#153]
+- *(1) Filter (isnotnull(person_country#153) && (person_country#153 = Cuba))
   +- *(1) FileScan csv [person_name#152,person_country#153] Batched: false, Format: CSV, Location: InMemoryFileIndex[file:/Users/matthewpowers/Documents/code/my_apps/mungingdata/spark2/src/test/re..., PartitionFilters: [], PushedFilters: [IsNotNull(person_country), EqualTo(person_country,Cuba)], ReadSchema: struct<person_name:string,person_country:string>

The syntax doesn't change how filters are executed under the hood, but the file format / database that a query is executed on does. Spark will execute the same query differently on Postgres (predicate pushdown filtering is supported), Parquet (column pruning), and CSV files. See here for more details.

How to write dynamic variable in Ansible playbook

my_var: the variable declared

VAR: the variable, whose value is to be checked

param_1, param_2: values of the variable VAR

value_1, value_2, value_3: the values to be assigned to my_var according to the values of my_var

my_var: "{{ 'value_1' if VAR == 'param_1' else 'value_2' if VAR == 'param_2' else 'value_3' }}"

How do I display a ratio in Excel in the format A:B?

At work we only have Excel 2003 available and these two formulas seem to work perfectly for me:




Converting NSString to NSDictionary / JSON

I believe you are misinterpreting the JSON format for key values. You should store your string as

NSString *jsonString = @"{\"ID\":{\"Content\":268,\"type\":\"text\"},\"ContractTemplateID\":{\"Content\":65,\"type\":\"text\"}}";
NSData *data = [jsonString dataUsingEncoding:NSUTF8StringEncoding];
id json = [NSJSONSerialization JSONObjectWithData:data options:0 error:nil];

Now if you do following NSLog statement

NSLog(@"%@",[json objectForKey:@"ID"]);

Result would be another NSDictionary.

    Content = 268;
    type = text;

Hope this helps to get clear understanding.

Shortcut to Apply a Formula to an Entire Column in Excel

Try double-clicking on the bottom right hand corner of the cell (ie on the box that you would otherwise drag).

resource error in android studio after update: No Resource Found

in your projects build.gradle file... write as below.. i have solved that error by change the appcompat version from v7.23.0.0 to v7.22.2.1..



compile fileTree(dir: 'libs', include: ['*.jar'])
compile ''


Below screen shot is for better understanding.

nginx 502 bad gateway

You can make nginx ignore client aborts using:

location / {
  proxy_ignore_client_abort on;

Taking the record with the max date

Since Oracle 12C, you can fetch a specific number of rows with FETCH FIRST ROW ONLY. In your case this implies an ORDER BY, so the performance should be considered.

SELECT A, col_date

The NULLS LAST is just in case you may have null values in your field.

Xampp MySQL not starting - "Attempting to start MySQL service..."

One of many reasons is xampp cannot start MySQL service by itself. Everything you need to do is run mySQL service manually.

First, make sure that 'mysqld.exe' is not running, if have, end it. (go to Task Manager > Progresses Tab > right click 'mysqld.exe' > end task)

Open your services.msc by Run (press 'Window + R') > services.msc or 0n your XAMPP ControlPanel, click 'Services' button. Find 'MySQL' service, right click and run it.

What is a Data Transfer Object (DTO)?


A DTO is a hardcoded data model. It only solves the problem of modeling a data record handled by a hardcoded production process, where all fields are known at compile-time and therefore accessed via strongly typed properties.

In contrast, a dynamic model or "property bag" solves the problem of modeling a data record when the production process is created at runtime.

The Cvar

A DTO can be modeled with fields or properties, but someone invented a very useful data container called the Cvar. It is a reference to a value. When a DTO is modeled with what I call reference properties, modules can be configured to share heap memory and thereby collaboratively work on it. This completely eliminates parameter passing and O2O communication from your code. In other words, DTOs having reference properties allow code to achieve zero coupling.

    class Cvar { ... }

    class Cvar<T> : Cvar
        public T Value { get; set; }

    class MyDTO
        public Cvar<int> X { get; set; }
        public Cvar<int> Y { get; set; }
        public Cvar<string> mutableString { get; set; } // >;)


Dynamic DTOs are a necessary component for dynamic software. To instantiate a dynamic process, one compiler step is to bind each machine in the script to the reference properties the script defines. A dynamic DTO is built by adding the Cvars to a collection.

    // a dynamic DTO
    class CvarRegistry : Dictionary<string, Cvar> { }


Note: because Wix labeled the use of DTOs for organizing parameters as an "anti-pattern", I will give an authoritative opinion.

    return View(model);  // MVC disagrees

My collaborative architecture replaces design patterns. Refer to my web articles.

Parameters provide immediate control of a stack frame machine. If you use continuous control and therefore do not need immediate control, your modules do not need parameters. My architecture has none. In-process configuration of machines (methods) adds complexity but also value (performance) when the parameters are value types. However, reference type parameters make the consumer cause cache misses to get the values off the heap anyway -- therefore, just configure the consumer with reference properties. Fact from mechanical engineering: reliance on parameters is a kind of preoptimization, because processing (making components) itself is waste. Refer to my W article for more information.

Fowler and company might realize the benefits of DTOs outside of distributed architecture if they had ever known any other architecture. Programmers only know distributed systems. Integrated collaborative systems (aka production aka manufacturing) are something I had to claim as my own architecture, because I am the first to write code this way.

Some consider the DTO an anemic domain model, meaning it lacks functionality, but this assumes an object must own the data it interacts with. This conceptual model then forces you to deliver the data between objects, which is the model for distributed processing. However on a manufacturing line, each step can access the end product and change it without owning or controlling it. That's the difference between distributed and integrated processing. Manufacturing separates the product from operations and logistics.

There's nothing inherently wrong with modeling processing as a bunch of useless office workers who e-mail work to one another without keeping an e-mail trail, except for all the extra work and headache it creates in handling logistics and return problems. A properly modeled distributed process attaches a document (active routing) to the product describing what operations it came from and will go to. The active routing is a copy of the process source routing, which is written before the process begins. In the event of a defect or other emergency change, the active routing is modified to include the operation steps it will be sent to. This then accounts for all the labor which went into production.

How to maintain page scroll position after a jquery event is carried out?

Try the code below to prevent the default behaviour scrolling back to the top of the page

$(document).ready(function() {   
  $('.galleryicon').live("click", function(e) {  // the (e) represent the event
    $('#cakebox').css('background-image', "url('ajax-loader.gif')");     
    var i = $('<img />').attr('src',this.href).load(function() {         
      $('#mainImage').attr('src', i.attr('src'));         
      $('#cakebox').css('background-image', 'none');         
  e.preventDefault(); //Prevent default click action which is causing the 
  return false;       //page to scroll back to the top

For more information on event.preventDefault() have a look here at the official documentation.

keypress, ctrl+c (or some combo like that)

You cannot use Ctrl+C by jQuery , but you can with another library which is shortcut.js

Live Demo : Abdennour JSFiddle

$(document).ready(function() {
shortcut.add("Ctrl+C", function() {
    $('span').html("?????. ??? ???? ??? ???? : Ctrl+C");
    shortcut.add("Ctrl+V", function() {
    $('span').html("?????. ??? ???? ??? ???? : Ctrl+V");
       shortcut.add("Ctrl+X", function() {
    $('span').html("?????. ??? ???? ??? ???? : Ctrl+X");


Using jquery to get element's position relative to viewport

jQuery.offset needs to be combined with scrollTop and scrollLeft as shown in this diagram:

viewport scroll and element offset


function getViewportOffset($e) {_x000D_
  var $window = $(window),_x000D_
    scrollLeft = $window.scrollLeft(),_x000D_
    scrollTop = $window.scrollTop(),_x000D_
    offset = $e.offset(),_x000D_
    rect1 = { x1: scrollLeft, y1: scrollTop, x2: scrollLeft + $window.width(), y2: scrollTop + $window.height() },_x000D_
    rect2 = { x1: offset.left, y1:, x2: offset.left + $e.width(), y2: + $e.height() };_x000D_
  return {_x000D_
    left: offset.left - scrollLeft,_x000D_
    top: - scrollTop,_x000D_
    insideViewport: rect1.x1 < rect2.x2 && rect1.x2 > rect2.x1 && rect1.y1 < rect2.y2 && rect1.y2 > rect2.y1_x000D_
$(window).on("load scroll resize", function() {_x000D_
  var viewportOffset = getViewportOffset($("#element"));_x000D_
  $("#log").text("left: " + viewportOffset.left + ", top: " + + ", insideViewport: " + viewportOffset.insideViewport);_x000D_
body { margin: 0; padding: 0; width: 1600px; height: 2048px; background-color: #CCCCCC; }_x000D_
#element { width: 384px; height: 384px; margin-top: 1088px; margin-left: 768px; background-color: #99CCFF; }_x000D_
#log { position: fixed; left: 0; top: 0; font: medium monospace; background-color: #EEE8AA; }
<script src=""></script>_x000D_
<!-- scroll right and bottom to locate the blue square -->_x000D_
<div id="element"></div>_x000D_
<div id="log"></div>

How to style child components from parent component's CSS file?

For assigning an element's class in a child component you can simply use an @Input string in the child's component and use it as an expression inside the template. Here is an example of something we did to change the icon and button type in a shared Bootstrap loading button component, without affecting how it was already used throughout the codebase:

app-loading-button.component.html (child)

<button class="btn {{additionalClasses}}">...</button>


@Input() additionalClasses: string;


<app-loading-button additionalClasses="fa fa-download btn-secondary">...</app-loading-button>

How to multiply all integers inside list

The simplest way to me is:

map((2).__mul__, [1, 2, 3])

Java Keytool error after importing certificate , "keytool error: & Access Denied"

I even run the command prompt as Administrator but it didn't work for me with the below error.

'keytool' is not recognized as an internal or external command,
 operable program or batch file.

If the path to the keytool is not in your System paths then you will need to use the full path to use the keytool, which is

C:\Program Files\Java\jre<version>\bin

So, the command should be like

"C:\Program Files\Java\jre<version>\bin\keytool.exe" -importcert -alias certificateFileAlias -file CertificateFileName.cer -keystore cacerts

that worked for me.

Linq to SQL .Sum() without group ... into

you can:


To hit the db only once do:

var itemsInCart = (from o in db.OrderLineItems
                  where o.OrderId == currentOrder.OrderId
                  select new { o.OrderLineItemId, ..., ..., o.WishListItem.Price}
var sum = itemsCart.Select(c=>c.Price).Sum();

The extra round-trip saved is worth it :)

Div Size Automatically size of content

The easiest is:

width: fit-content;

Auto increment in MongoDB to store sequence of Unique User ID

You can, but you should not

Each object in mongo already has an id, and they are sortable in insertion order. What is wrong with getting collection of user objects, iterating over it and use this as incremented ID? Er go for kind of map-reduce job entirely

pandas create new column based on values from other columns / apply a function of multiple columns, row-wise

Since this is the first Google result for 'pandas new column from others', here's a simple example:

import pandas as pd

# make a simple dataframe
df = pd.DataFrame({'a':[1,2], 'b':[3,4]})
#    a  b
# 0  1  3
# 1  2  4

# create an unattached column with an index
df.apply(lambda row: row.a + row.b, axis=1)
# 0    4
# 1    6

# do same but attach it to the dataframe
df['c'] = df.apply(lambda row: row.a + row.b, axis=1)
#    a  b  c
# 0  1  3  4
# 1  2  4  6

If you get the SettingWithCopyWarning you can do it this way also:

fn = lambda row: row.a + row.b # define a function for the new column
col = df.apply(fn, axis=1) # get column data with an index
df = df.assign(c=col.values) # assign values to column 'c'


And if your column name includes spaces you can use syntax like this:

df = df.assign(**{'some column name': col.values})

And here's the documentation for apply, and assign.

How to get current language code with Swift?

To get current language used in your app (different than preferred languages)


What is best tool to compare two SQL Server databases (schema and data)?

I've used SQL Delta before (, it's really good. Not free however, not sure how prices compare to Red-Gates

Is there a standard function to check for null, undefined, or blank variables in JavaScript?

! check for empty strings (""), null, undefined, false and the number 0 and NaN. Say, if a string is empty var name = "" then console.log(!name) returns true.

function isEmpty(val){
  return !val;

this function will return true if val is empty, null, undefined, false, the number 0 or NaN.


According to your problem domain you can just use like !val or !!val.

Setting up a websocket on Apache?

The new version 2.4 of Apache HTTP Server has a module called mod_proxy_wstunnel which is a websocket proxy.

Separation of business logic and data access in django

I would have to agree with you. There are a lot of possibilities in django but best place to start is reviewing Django's design philosophy.

  1. Calling an API from a model property would not be ideal, it seems like it would make more sense to do something like this in the view and possibly create a service layer to keep things dry. If the call to the API is non-blocking and the call is an expensive one, sending the request to a service worker (a worker that consumes from a queue) might make sense.

  2. As per Django's design philosophy models encapsulate every aspect of an "object". So all business logic related to that object should live there:

Include all relevant domain logic

Models should encapsulate every aspect of an “object,” following Martin Fowler’s Active Record design pattern.

  1. The side effects you describe are apparent, the logic here could be better broken down into Querysets and managers. Here is an example:

    import datetime
    from djongo import models
    from django.db.models.query import QuerySet
    from django.contrib import admin
    from django.db import transaction
    class MyUser(models.Model):
        present_name = models.TextField(null=False, blank=True)
        status = models.TextField(null=False, blank=True)
        last_active = models.DateTimeField(auto_now=True, editable=False)
        # As mentioned you could put this in a template tag to pull it
        # from cache there. Depending on how it is used, it could be
        # retrieved from within the admin view or from a custom view
        # if that is the only place you will use it.
        #def get_present_name(self):
        #    # property became non-deterministic in terms of database
        #    # data is taken from another service by api
        #    return remote_api.request_user_name(self.uid) or 'Anonymous'
        # Moved to admin as an action
        # def activate(self):
        #     # method now has a side effect (send message to user)
        #     self.status = 'activated'
        #     # send email via email service
        #     #send_mail('Your account is activated!', '…', [])
        class Meta:
            ordering = ['-id']  # Needed for DRF pagination
        def __unicode__(self):
            return '{}'.format(
    class MyUserRegistrationQuerySet(QuerySet):
        def for_inactive_users(self):
            new_date = - datetime.timedelta(days=3*365)  # 3 Years ago
            return self.filter(last_active__lte=new_date.year)
        def by_user_id(self, user_ids):
            return self.filter(id__in=user_ids)
    class MyUserRegistrationManager(models.Manager):
        def get_query_set(self):
            return MyUserRegistrationQuerySet(self.model, using=self._db)
        def with_no_activity(self):
            return self.get_query_set().for_inactive_users()

    # Then in model admin
    class MyUserRegistrationAdmin(admin.ModelAdmin):
        actions = (
        def send_activate_emails(self, request, queryset):
            rows_affected = 0
            for obj in queryset:
                with transaction.commit_on_success():
                    # send_email('welcome_email', request, obj) # send email via email service
                    obj.status = 'activated'
                    rows_affected += 1
            self.message_user(request, 'sent %d' % rows_affected), MyUserRegistrationAdmin)

Replace non-numeric with empty string

for the best performance and lower memory consumption , try this:

using System;
using System.Diagnostics;
using System.Text;
using System.Text.RegularExpressions;

public class Program
    private static Regex digitsOnly = new Regex(@"[^\d]");

    public static void Main()

        string phone = "001-12-34-56-78-90";

        var sw = new Stopwatch();
        for (int i = 0; i < 1000000; i++)
        Console.WriteLine("Time: " + sw.ElapsedMilliseconds);

        var sw2 = new Stopwatch();
        for (int i = 0; i < 1000000; i++)
        Console.WriteLine("Time: " + sw2.ElapsedMilliseconds);


    public static string DigitsOnly(string phone, string replace = null)
        if (replace == null) replace = "";
        if (phone == null) return null;
        var result = new StringBuilder(phone.Length);
        foreach (char c in phone)
            if (c >= '0' && c <= '9')
        return result.ToString();

    public static string DigitsOnlyRegex(string phone)
        return digitsOnly.Replace(phone, "");

The result in my computer is:
Time: 307
Time: 2178

Understanding the set() function

Sets are unordered, as you say. Even though one way to implement sets is using a tree, they can also be implemented using a hash table (meaning getting the keys in sorted order may not be that trivial).

If you'd like to sort them, you can simply perform:


which will produce a sorted list containing the set's elements. (Not a set. Again, sets are unordered.)

Otherwise, the only thing guaranteed by set is that it makes the elements unique (nothing will be there more than once).

Hope this helps!

An object reference is required to access a non-static member

I'm guessing you get the error on accessing audioSounds and minTime, right?

The problem is you can't access instance members from static methods. What this means is that, a static method is a method that exists only once and can be used by all other objects (if its access modifier permits it).

Instance members, on the other hand, are created for every instance of the object. So if you create ten instances, how would the runtime know out of all these instances, which audioSounds list it should access?

Like others said, make your audioSounds and minTime static, or you could make your method an instance method, if your design permits it.

Extract matrix column values by matrix column name

Yes. But place your "test" after the comma if you want the column...

> A <- matrix(sample(1:12,12,T),ncol=4)

> rownames(A) <- letters[1:3]

> colnames(A) <- letters[11:14]
> A[,"l"]
 a  b  c 
 6 10  1 

see also help(Extract)

PLS-00103: Encountered the symbol when expecting one of the following:

    var_number := 10;

    if var_number > 100 then
        dbms_output.put_line(var_number||' is greater than 100');
    else if var_number < 100 then
        dbms_output.put_line(var_number||' is less than 100');
        dbms_output.put_line(var_number||' is equal to 100');
    end if;
end if;

Using Apache POI how to read a specific excel column

heikkim is right, here is some sample code adapted from some code I have:

for (int rowIndex = 0; rowIndex <= sheet.getLastRowNum(); rowIndex++) {
  row = sheet.getRow(rowIndex);
  if (row != null) {
    Cell cell = row.getCell(colIndex);
    if (cell != null) {
      // Found column and there is value in the cell.
      cellValueMaybeNull = cell.getStringCellValue();
      // Do something with the cellValueMaybeNull here ...
      // break; ???

For the colCount use something like row.getPhysicalNumberOfCells()

What's the Kotlin equivalent of Java's String[]?

To create an empty Array of Strings in Kotlin you should use one of the following six approaches:

First approach:

val empty = arrayOf<String>()

Second approach:

val empty = arrayOf("","","")

Third approach:

val empty = Array<String?>(3) { null }

Fourth approach:

val empty = arrayOfNulls<String>(3)

Fifth approach:

val empty = Array<String>(3) { "it = $it" }

Sixth approach:

val empty = Array<String>(0, { _ -> "" })

How to take off line numbers in Vi?

Display line numbers:

:set nu

Stop showing the line numbers:

:set nonu

Its short for :set nonumber

ps. These commands are to be run in normal mode.

Promise.all().then() resolve?

But that doesn't seem like the proper way to do it..

That is indeed the proper way to do it (or at least a proper way to do it). This is a key aspect of promises, they're a pipeline, and the data can be massaged by the various handlers in the pipeline.


const promises = [_x000D_
  new Promise(resolve => setTimeout(resolve, 0, 1)),_x000D_
  new Promise(resolve => setTimeout(resolve, 0, 2))_x000D_
  .then(data => {_x000D_
    console.log("First handler", data);_x000D_
    return => entry * 10);_x000D_
  .then(data => {_x000D_
    console.log("Second handler", data);_x000D_

(catch handler omitted for brevity. In production code, always either propagate the promise, or handle rejection.)

The output we see from that is:

First handler [1,2]
Second handler [10,20]

...because the first handler gets the resolution of the two promises (1 and 2) as an array, and then creates a new array with each of those multiplied by 10 and returns it. The second handler gets what the first handler returned.

If the additional work you're doing is synchronous, you can also put it in the first handler:


const promises = [_x000D_
  new Promise(resolve => setTimeout(resolve, 0, 1)),_x000D_
  new Promise(resolve => setTimeout(resolve, 0, 2))_x000D_
  .then(data => {_x000D_
    console.log("Initial data", data);_x000D_
    data = => entry * 10);_x000D_
    console.log("Updated data", data);_x000D_
    return data;_x000D_

...but if it's asynchronous you won't want to do that as it ends up getting nested, and the nesting can quickly get out of hand.

How to cherry pick a range of commits and merge into another branch?

Assume that you have 2 branches,

"branchA" : includes commits you want to copy (from "commitA" to "commitB"

"branchB" : the branch you want the commits to be transferred from "branchA"


 git checkout <branchA>

2) get the IDs of "commitA" and "commitB"


git checkout <branchB>


git cherry-pick <commitA>^..<commitB>

5) In case you have a conflict, solve it and type

git cherry-pick --continue

to continue the cherry-pick process.

Getting "error": "unsupported_grant_type" when trying to get a JWT by calling an OWIN OAuth secured Web Api via Postman

I was getting this error too and the reason ended up being wrong call url. I am leaving this answer here, if someone else happens to mix the urls and getting this error. Took me hours to realize I had wrong URL.

Error I got (HTTP code 400):

    "error": "unsupported_grant_type",
    "error_description": "grant type not supported"

I was calling:

While the correct URL would have been:

Find duplicates and delete all in notepad++

You need the textFX plugin. Then, just follow these instructions:

Paste the text into Notepad++ (CTRL+V). ...
Mark all the text (CTRL+A). ...
Click TextFX ? Click TextFX Tools ? Click Sort lines case insensitive (at column)
Duplicates and blank lines have been removed and the data has been sorted alphabetically.

Personally, I would use sort -i -u source >dest instead of notepad++

What's the better (cleaner) way to ignore output in PowerShell?

I just did some tests of the four options that I know about.

Measure-Command {$(1..1000) | Out-Null}

TotalMilliseconds : 76.211

Measure-Command {[Void]$(1..1000)}

TotalMilliseconds : 0.217

Measure-Command {$(1..1000) > $null}

TotalMilliseconds : 0.2478

Measure-Command {$null = $(1..1000)}

TotalMilliseconds : 0.2122

## Control, times vary from 0.21 to 0.24
Measure-Command {$(1..1000)}

TotalMilliseconds : 0.2141

So I would suggest that you use anything but Out-Null due to overhead. The next important thing, to me, would be readability. I kind of like redirecting to $null and setting equal to $null myself. I use to prefer casting to [Void], but that may not be as understandable when glancing at code or for new users.

I guess I slightly prefer redirecting output to $null.

Do-Something > $null


After stej's comment again, I decided to do some more tests with pipelines to better isolate the overhead of trashing the output.

Here are some tests with a simple 1000 object pipeline.

## Control Pipeline
Measure-Command {$(1..1000) | ?{$_ -is [int]}}

TotalMilliseconds : 119.3823

## Out-Null
Measure-Command {$(1..1000) | ?{$_ -is [int]} | Out-Null}

TotalMilliseconds : 190.2193

## Redirect to $null
Measure-Command {$(1..1000) | ?{$_ -is [int]} > $null}

TotalMilliseconds : 119.7923

In this case, Out-Null has about a 60% overhead and > $null has about a 0.3% overhead.

Addendum 2017-10-16: I originally overlooked another option with Out-Null, the use of the -inputObject parameter. Using this the overhead seems to disappear, however the syntax is different:

Out-Null -inputObject ($(1..1000) | ?{$_ -is [int]})

And now for some tests with a simple 100 object pipeline.

## Control Pipeline
Measure-Command {$(1..100) | ?{$_ -is [int]}}

TotalMilliseconds : 12.3566

## Out-Null
Measure-Command {$(1..100) | ?{$_ -is [int]} | Out-Null}

TotalMilliseconds : 19.7357

## Redirect to $null
Measure-Command {$(1..1000) | ?{$_ -is [int]} > $null}

TotalMilliseconds : 12.8527

Here again Out-Null has about a 60% overhead. While > $null has an overhead of about 4%. The numbers here varied a bit from test to test (I ran each about 5 times and picked the middle ground). But I think it shows a clear reason to not use Out-Null.

JetBrains / IntelliJ keyboard shortcut to collapse all methods

In Rider, this would be Ctrl +Shift+Keypad *, 2

But!, you cannot use the number 2 on keypad, only number 2 on the top row of the keyboard would work.

Pan & Zoom Image

One addition to the superb solution provided by @Wieslaw Šoltés answer above

The existing code resets the image position using right click, but I am more accustomed to doing that with a double click. Just replace the existing child_MouseLeftButtonDown handler:

private void child_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
        if (child != null)
            var tt = GetTranslateTransform(child);
            start = e.GetPosition(this);
            origin = new Point(tt.X, tt.Y);
            this.Cursor = Cursors.Hand;

With this:

private void child_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
        if ((e.ChangedButton == MouseButton.Left && e.ClickCount == 1))
            if (child != null)
                var tt = GetTranslateTransform(child);
                start = e.GetPosition(this);
                origin = new Point(tt.X, tt.Y);
                this.Cursor = Cursors.Hand;

        if ((e.ChangedButton == MouseButton.Left && e.ClickCount == 2))

How do I select which GPU to run a job on?

Set the following two environment variables:


where gpu_id is the ID of your selected GPU, as seen in the host system's nvidia-smi (a 0-based integer) that will be made available to the guest system (e.g. to the Docker container environment).

You can verify that a different card is selected for each value of gpu_id by inspecting Bus-Id parameter in nvidia-smi run in a terminal in the guest system).

More info

This method based on NVIDIA_VISIBLE_DEVICES exposes only a single card to the system (with local ID zero), hence we also hard-code the other variable, CUDA_VISIBLE_DEVICES to 0 (mainly to prevent it from defaulting to an empty string that would indicate no GPU).

Note that the environmental variable should be set before the guest system is started (so no chances of doing it in your Jupyter Notebook's terminal), for instance using docker run -e NVIDIA_VISIBLE_DEVICES=0 or env in Kubernetes or Openshift.

If you want GPU load-balancing, make gpu_id random at each guest system start.

If setting this with python, make sure you are using strings for all environment variables, including numerical ones.

You can verify that a different card is selected for each value of gpu_id by inspecting nvidia-smi's Bus-Id parameter (in a terminal run in the guest system).

The accepted solution based on CUDA_VISIBLE_DEVICES alone does not hide other cards (different from the pinned one), and thus causes access errors if you try to use them in your GPU-enabled python packages. With this solution, other cards are not visible to the guest system, but other users still can access them and share their computing power on an equal basis, just like with CPU's (verified).

This is also preferable to solutions using Kubernetes / Openshift controlers (, that would impose a lock on the allocated card, removing it from the pool of available resources (so the number of containers with GPU access could not exceed the number of physical cards).

This has been tested under CUDA 8.0, 9.0 and 10.1 in docker containers running Ubuntu 18.04 orchestrated by Openshift 3.11.

Comparing two .jar files

Extract each jar to it's own directory using the jar command with parameters xvf. i.e. jar xvf myjar.jar for each jar.

Then, use the UNIX command diff to compare the two directories. This will show the differences in the directories. You can use diff -r dir1 dir2 two recurse and show the differences in text files in each directory(.xml, .properties, etc).

This will also show if binary class files differ. To actually compare the class files you will have to decompile them as noted by others.

How to annotate MYSQL autoincrement field with JPA annotations

For anyone reading this who is using EclipseLink for JPA 2.0, here are the two annotations I had to use to get JPA to persist data, where "MySequenceGenerator" is whatever name you want to give the generator, "myschema" is the name of the schema in your database that contains the sequence object, and "mysequence" is the name of the sequence object in the database.

@GeneratedValue(strategy= GenerationType.SEQUENCE, generator="MySequenceGenerator")
@SequenceGenerator(allocationSize=1, schema="myschema",  name="MySequenceGenerator", sequenceName = "mysequence")

For those using EclipseLink (and possibly other JPA providers), it is CRITICAL that you set the allocationSize attribute to match the INCREMENT value defined for your sequence in the database. If you don't, you'll get a generic persistence failure, and waste a good deal of time trying to track it down, like I did. Here is the reference page that helped me overcome this challenge:

Also, to give context, here is what we're using:

Java 7 Glassfish 3.1 PostgreSQL 9.1 PrimeFaces 3.2/JSF 2.1

Also, for laziness' sake, I built this in Netbeans with the wizards for generating Entities from DB, Controllers from Entities, and JSF from Entities, and the wizards (obviously) do not know how to deal with sequence-based ID columns, so you'll have to manually add these annotations.

Convert Decimal to Varchar

If you are using SQL Server 2012, 2014 or newer, use the Format Function instead:

select Format( decimalColumnName ,'FormatString','en-US' )

Review the Microsoft topic and .NET format syntax for how to define the format string.

An example for this question would be:

select Format( MyDecimalColumn ,'N','en-US' )

Mac OS X - EnvironmentError: mysql_config not found

I had been debugging this problem forever - 3 hours 17 mins. What particularly annoyed me was that I already had sql installed on my system through prior uni work but pip/pip3 wasn't recognising it. These threads above and many other I scoured the internet for were helpful in eluminating the problem but didn't actually solve things.


Pip is looking for mysql binaries in the Homebrew Directory which is located relative to Macintosh HD @


so I found that this requires you making a few changes

step 1: Download MySql if not already done so

Step 2: Locate it relative to Macintosh HD and cd


Step 3: Once there open terminal and use a text editor of choice - I'm a neovim guy myself so I typed (doesn't automatically come with Mac... another story for another day)

nvim mysql_config

Step 4: You will see at approx line 112

# Create options 
libs="$libs -l "

Change to

# Create options 
libs="$libs -lmysqlclient -lssl -lcrypto"

*you'll notice that this file has read-only access so if your using vim or neovim

:w !sudo tee %

Step 5: Head to the home directory and edit the .bash_profile file

cd ~


nvim .bash_profile

and add

export PATH="/usr/local/mysql/bin:$PATH"

to the file then save

Step 6: relative to Macintosh HD locate paths and add to it

cd /private/etc/


nvim paths

and add


*you'll again notice that this file has read-only access so if your using vim or neovim

:w !sudo tee % 


cd ~

then refresh the terminal with your changes by running

source .bash_profile


pip3 install mysqlclient

And Viola. Remember it's a vibe.

What is the copy-and-swap idiom?

This answer is more like an addition and a slight modification to the answers above.

In some versions of Visual Studio (and possibly other compilers) there is a bug that is really annoying and doesn't make sense. So if you declare/define your swap function like this:

friend void swap(A& first, A& second) {

    std::swap(first.size, second.size);
    std::swap(first.arr, second.arr);


... the compiler will yell at you when you call the swap function:

enter image description here

This has something to do with a friend function being called and this object being passed as a parameter.

A way around this is to not use friend keyword and redefine the swap function:

void swap(A& other) {

    std::swap(size, other.size);
    std::swap(arr, other.arr);


This time, you can just call swap and pass in other, thus making the compiler happy:

enter image description here

After all, you don't need to use a friend function to swap 2 objects. It makes just as much sense to make swap a member function that has one other object as a parameter.

You already have access to this object, so passing it in as a parameter is technically redundant.

Iterate over object keys in node.js

For simple iteration of key/values, sometimes libraries like underscorejs can be your friend.

const _ = require('underscore');

_.each(a, function (value, key) {
    // handle

just for reference

Practical uses for AtomicInteger

Like gabuzo said, sometimes I use AtomicIntegers when I want to pass an int by reference. It's a built-in class that has architecture-specific code, so it's easier and likely more optimized than any MutableInteger I could quickly code up. That said, it feels like an abuse of the class.

HTML combo box with option to type an entry

The dojo example here do not work when applied to existing code in most cases. Therefor I had to find an alternate, found here - hxxp:// (now points to a spam site or worse) (not very useful)

Here is the jsfiddle -

Get environment value in controller

It's a better idea to put your configuration variables in a configuration file.

In your case, I would suggest putting your variables in config/mail.php like:

'imap_hostname' => env('IMAP_HOSTNAME_TEST', '')

And refer to them by


It first tries to get the configuration variable value in the .env file and if it couldn't find the variable value in the .env file, it will get the variable value from file config/mail.php.

Python Requests - No connection adapters

One more reason, maybe your url include some hiden characters, such as '\n'.

If you define your url like below, this exception will raise:

url = '''

because there are '\n' hide in the string. The url in fact become:


Working with a List of Lists in Java

If you are really like to know that handle CSV files perfectly in Java, it's not good to try to implement CSV reader/writer by yourself. Check below out.

When your CSV document includes double-quotes or newlines, you will face difficulties.

To learn object-oriented approach at first, seeing other implementation (by Java) will help you. And I think it's not good way to manage one row in a List. CSV doesn't allow you to have difference column size.

Output to the same line overwriting previous output?

Have a look at the curses module documentation and the curses module HOWTO.

Really basic example:

import time
import curses

stdscr = curses.initscr()

stdscr.addstr(0, 0, "Hello")


stdscr.addstr(0, 0, "World! (with curses)")

Django CSRF Cookie Not Set

Make sure your django session backend is configured properly in Then try this,

class CustomMiddleware(object):
  def process_request(self,request:HttpRequest):

Add this middleware in under MIDDLEWARE_CLASSES or MIDDLEWARE depending on the django version

get_token - Returns the CSRF token required for a POST form. The token is an alphanumeric value. A new token is created if one is not already set.

How to convert NSNumber to NSString

or try NSString *string = [NSString stringWithFormat:@"%d", [NSNumber intValue], nil];

How to add a search box with icon to the navbar in Bootstrap 3?

You could use the segmented buttons example from Bootstrap 3:

<form action="" class="navbar-form navbar-right">
   <div class="input-group">
       <input type="Search" placeholder="Search..." class="form-control" />
       <div class="input-group-btn">
           <button class="btn btn-info">
           <span class="glyphicon glyphicon-search"></span>

Change table header color using bootstrap

there's a bootstrap function to change the color of table header called thead-dark for dark background of table header and thead-light for light background of table header. Your code will look like this after using this function.

<table class="table">
    <tr class="thead-danger">
        <!-- here I used dark table headre -->
            @Html.DisplayNameFor(model =>
            @Html.DisplayNameFor(model => model.checkBox1)

Creating an abstract class in Objective-C

If you are used to the compiler catching abstract instantiation violations in other languages, then the Objective-C behavior is disappointing.

As a late binding language it is clear that Objective-C cannot make static decisions on whether a class truly is abstract or not (you might be adding functions at runtime...), but for typical use cases this seems like a shortcoming. I would prefer the compiler flat-out prevented instantiations of abstract classes instead of throwing an error at runtime.

Here is a pattern we are using to get this type of static checking using a couple of techniques to hide initializers:

//  Base.h
#define UNAVAILABLE __attribute__((unavailable("Default initializer not available.")));

@protocol MyProtocol <NSObject>
-(void) dependentFunction;

@interface Base : NSObject {
    __weak id<MyProtocol> _protocolHelper; // Weak to prevent retain cycles!

- (instancetype) init UNAVAILABLE; // Prevent the user from calling this
- (void) doStuffUsingDependentFunction;

//  Base.m
#import "Base.h"

// We know that Base has a hidden initializer method.
// Declare it here for readability.
@interface Base (Private)
- (instancetype)initFromDerived;

@implementation Base
- (instancetype)initFromDerived {
    // It is unlikely that this becomes incorrect, but assert
    // just in case.
    NSAssert(![self isMemberOfClass:[Base class]],
             @"To be called only from derived classes!");
    self = [super init];
    return self;

- (void) doStuffUsingDependentFunction {
    [_protocolHelper dependentFunction]; // Use it

//  Derived.h
#import "Base.h"

@interface Derived : Base
-(instancetype) initDerived; // We cannot use init here :(

//  Derived.m
#import "Derived.h"

// We know that Base has a hidden initializer method.
// Declare it here.
@interface Base (Private)
- (instancetype) initFromDerived;

// Privately inherit protocol
@interface Derived () <MyProtocol>

@implementation Derived
-(instancetype) initDerived {
    self= [super initFromDerived];
    if (self) {
        self->_protocolHelper= self;
    return self;

// Implement the missing function
-(void)dependentFunction {

How to find out the location of currently used MySQL configuration file in linux

mysqld --help --verbose will find only location of default configuration file. What if you use 2 MySQL instances on the same server? It's not going to help.

Good article about figuring it out:

"How to find MySQL configuration file?"

How to calculate time difference in java?

Java 8

DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");

LocalDateTime dateTime1= LocalDateTime.parse("2014-11-25 19:00:00", formatter);
LocalDateTime dateTime2= LocalDateTime.parse("2014-11-25 16:00:00", formatter);

long diffInMilli = java.time.Duration.between(dateTime1, dateTime2).toMillis();
long diffInSeconds = java.time.Duration.between(dateTime1, dateTime2).getSeconds();
long diffInMinutes = java.time.Duration.between(dateTime1, dateTime2).toMinutes();

How to do left join in Doctrine?

If you have an association on a property pointing to the user (let's say Credit\Entity\UserCreditHistory#user, picked from your example), then the syntax is quite simple:

public function getHistory($users) {
    $qb = $this->entityManager->createQueryBuilder();
        ->select('a', 'u')
        ->from('Credit\Entity\UserCreditHistory', 'a')
        ->leftJoin('a.user', 'u')
        ->where('u = :user')
        ->setParameter('user', $users)
        ->orderBy('a.created_at', 'DESC');

    return $qb->getQuery()->getResult();

Since you are applying a condition on the joined result here, using a LEFT JOIN or simply JOIN is the same.

If no association is available, then the query looks like following

public function getHistory($users) {
    $qb = $this->entityManager->createQueryBuilder();
        ->select('a', 'u')
        ->from('Credit\Entity\UserCreditHistory', 'a')
            'a.user ='
        ->where('u = :user')
        ->setParameter('user', $users)
        ->orderBy('a.created_at', 'DESC');

    return $qb->getQuery()->getResult();

This will produce a resultset that looks like following:

        0 => UserCreditHistory instance,
        1 => Userinstance,
        0 => UserCreditHistory instance,
        1 => Userinstance,
    // ...

How to put a tooltip on a user-defined function

A lot of dancing around the answer. You can add the UDF context help, but you have to export the Module and edit the contents in a text editor, then re-import it to VBA. Here's the example from Chip Pearson: Adding Code Attributes

Only numbers. Input number in React

You can try this solution, since onkeypress will be attached directly to the DOM element and will prevent users from entering invalid data to begin with.

So no side-effects on react side.

<input type="text" onKeyPress={onNumberOnlyChange}/>

const onNumberOnlyChange = (event: any) => {
    const keyCode = event.keyCode || event.which;
    const keyValue = String.fromCharCode(keyCode);
    const isValid = new RegExp("[0-9]").test(keyValue);
    if (!isValid) {

Querying a linked sql server

try Select * from openquery("aa-db-dev01",'Select * from users') ,the database connection should be defined in he linked server configuration

Click a button programmatically

The best practice for this sort of situation is to create a method that hold all the logics, and call the method in both events, rather than calling an event from another event;

Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click


End Sub

Protected Sub Button2_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click


End Sub

Private Sub LogicMethod()

     // All your logic goes here

End Sub

In case you need the properties of the EventArgs (e), you can easily pass it through parameters in your method, that will avoid errors if ever the sender is of different types. But that won't be a problem in your case, as both senders are of type Button.

How do I make a "div" button submit the form its sitting in?

Are you aware of <button> elements? <button> elements can be styled just like <div> elements and can have type="submit" so they submit the form without javascript:

<form action="whatever.html" method="post">  
    <button name="mysubmitbutton" id="mysubmitbutton" type="submit" class="customButton">  
    Button Text

Using a <button> is also more semantic, whereas <div> is very generic. You get the following benefits for free:

  • JavaScript is not necessary to submit the form
  • Accessibility tools, e.g. screen readers, will (correctly) treat it as a button and not part of the normal text flow
  • <button type="submit"> becomes a "default" button, which means the return key will automatically submit the form. You can't do this with a <div>, you'd have to add a separate keydown handler to the <form> element.

There's one (non-) caveat: a <button> can only have phrasing content, though it's unlikely anyone would need any other type of content when using the element to submit a form.

How to make a Qt Widget grow with the window size?

The accepted answer (its image) is wrong, at least now in QT5. Instead you should assign a layout to the root object/widget (pointing to the aforementioned image, it should be the MainWindow instead of centralWidget). Also note that you must have at least one QObject created beneath it for this to work. Do this and your ui will become responsive to window resizing.

How to restart counting from 1 after erasing table in MS Access?

I always use below approach. I've created one table in database as Table1 with only one column i.e. Row_Id Number (Long Integer) and its value is 0

enter image description here

FROM Table1;

This will insert one row with 0 value in AutoNumber column, later delete that row.

XPath query to get nth instance of an element

This seems to work:


I go this from "XSLT 2.0 and XPath 2.0 Programmer's Reference, 4th Edition" by Michael Kay.

There is also a note in the "Abbreviated Syntax" section of the XML Path Language specification that provided a clue.

Could not resolve placeholder in string value

This Issue occurs if the application is unable to access the file.Make sure that the properties file is placed under resources folder in spring.

Trouble shooting Steps

1: Add the properties file under the resource folder.

2: If you don't have a resource folder. Create one by navigating new by Right click on the project new > Source Folder, name it as resource and place your properties file under it.

For annotation based Implementation

Add @PropertySource(ignoreResourceNotFound = true, value = "")//Add it before using the place holder



@PropertySource(ignoreResourceNotFound = true, value = "")
public class Assignment1Controller {

//  @Autowired
//  Assignment1Services assignment1Services;
    private String appTitle;
     @RequestMapping(value = "/hello")  
        public String getValues() {

          return appTitle;



app.title=Learning Spring

Change color when hover a font awesome icon?

if you want to change only the colour of the flag on hover use this:

.fa-flag:hover {_x000D_
    color: red;_x000D_
<link href="" rel="stylesheet"/>_x000D_
<i class="fa fa-flag fa-3x"></i>

How to remove an unpushed outgoing commit in Visual Studio?

I fixed it in Github Desktop Application by pushing my changes.

How to concatenate characters in java?

this is very simple approach to concatenate or append the character

       StringBuilder desc = new StringBuilder(); 
       String Description="this is my land"; 

how to console.log result of this ajax call?

In Chrome, right click in the console and check 'preserve log on navigation'.

To enable extensions, verify that they are enabled in those .ini files - Vagrant/Ubuntu/Magento 2.0.2

I used below to fix issue

yum install -y php-intl php-xsl php-opcache php-xml php-mcrypt php-gd php-devel php-mysql php-mbstring php-bcmath

Break string into list of characters in Python

Strings are iterable (just like a list).

I'm interpreting that you really want something like:

fd = open(filename,'rU')
chars = []
for line in fd:
   for c in line:


fd = open(filename, 'rU')
chars = []
for line in fd:


chars = []
with open(filename, 'rU') as fd:
    map(chars.extend, fd)

chars would contain all of the characters in the file.

How to parse json string in Android?

Below is the link which guide in parsing JSON string in android.

Also according to your json string code snippet must be something like this:-

JSONObject mainObject = new JSONObject(yourstring);

JSONObject universityObject = mainObject.getJSONObject("university");
JSONString name = universityObject.getString("name");  
JSONString url = universityObject.getString("url");

Following is the API reference for JSOnObject:

Same for other object.

Disable Buttons in jQuery Mobile

uncaught exception: cannot call methods on button prior to initialization; attempted to call method 'disable'.

this means that you are trying to call it on an element that is not handled as a button, because no .button method was called on it. Therefore your problem MUST be the selector.

You are selecting all inputs $('input'), so it tries to call the method disable from button widget namespace not only on buttons, but on text inputs too.

$('button').attr("disabled", "disabled"); will not work with jQuery Mobile, because you modify the button that is hiden and replaced by a markup that jQuery Mobile generates.

You HAVE TO use jQueryMobile's method of disabling the button with a correct selector like:

$('div#DT1S input[type=button]').button('disable');

Skip to next iteration in loop vba

Just do nothing once the criteria is met, otherwise do the processing you require and the For loop will go to the next item.

For i = 2 To 24
    Level = Cells(i, 4)
    Return = Cells(i, 5)

    If Return = 0 And Level = 0 Then
        'Do nothing
        'Do something
    End If
Next i

Or change the clause so it only processes if the conditions are met:

For i = 2 To 24
    Level = Cells(i, 4)
    Return = Cells(i, 5)

    If Return <> 0 Or Level <> 0 Then
        'Do something
    End If
Next i

How to change cursor from pointer to finger using jQuery?

$('selector').css('cursor', 'pointer'); // 'default' to revert

I know that may be confusing per your original question, but the "finger" cursor is actually called "pointer".

The normal arrow cursor is just "default".

all possible default pointer looks DEMO

Change Project Namespace in Visual Studio

"Default Namespace textbox in project properties is disabled" Same with me (VS 2010). I edited the project file ("xxx.csproj") and tweaked the item. That changed the default namespace.

Apache won't follow symlinks (403 Forbidden)

There is another way that symbolic links may fail you, as I discovered in my situation. If you have an SELinux system as the server and the symbolic links point to an NFS-mounted folder (other file systems may yield similar symptoms), httpd may see the wrong contexts and refuse to serve the contents of the target folders.

In my case the SELinux context of /var/www/html (which you can obtain with ls -Z) is unconfined_u:object_r:httpd_sys_content_t:s0. The symbolic links in /var/www/html will have the same context, but their target's context, being an NFS-mounted folder, are system_u:object_r:nfs_t:s0.

The solution is to add fscontext=unconfined_u:object_r:httpd_sys_content_t:s0 to the mount options (e.g. # mount -t nfs -o v3,fscontext=unconfined_u:object_r:httpd_sys_content_t:s0 <IP address>:/<server path> /<mount point>). rootcontext is irrelevant and defcontext is rejected by NFS. I did not try context by itself.


ENABLEDELAYEDEXPANSION is a parameter passed to the SETLOCAL command (look at setlocal /?)

Its effect lives for the duration of the script, or an ENDLOCAL:

When the end of a batch script is reached, an implied ENDLOCAL is executed for any outstanding SETLOCAL commands issued by that batch script.

In particular, this means that if you use SETLOCAL ENABLEDELAYEDEXPANSION in a script, any environment variable changes are lost at the end of it unless you take special measures.

how to fix groovy.lang.MissingMethodException: No signature of method:

In my case it was simply that I had a variable named the same as a function.


def cleanCache = functionReturningABoolean()

if( cleanCache ){
    echo "Clean cache option is true, do not uninstall previous features / urls"
    uninstallCmd = ""
    // and we call the cleanCache method
    cleanCache(userId, serverName)

and later in my code I have the function:

def cleanCache(user, server){

 //some operations to the server


Apparently the Groovy language does not support this (but other languages like Java does). I just renamed my function to executeCleanCache and it works perfectly (or you can also rename your variable whatever option you prefer).

Return Boolean Value on SQL Select Statement

Notice another equivalent problem: Creating an SQL query that returns (1) if the condition is satisfied and an empty result otherwise. Notice that a solution to this problem is more general and can easily be used with the above answers to achieve the question that you asked. Since this problem is more general, I am proving its solution in addition to the beautiful solutions presented above to your problem.

FROM [User]
WHERE (UserID = 20070022)

What is the minimum I have to do to create an RPM file?

For quick RPM building, check out Togo:

The project has a Quick-Start guide and I was able to create a basic RPM in less than 3 minutes.

Example using the data provided in the original question:

1) Create the project directory using the script:

$ togo project create foobar; cd foobar

2) Make your desired directory structure under ./root and copy your files into it:

$ mkdir -p root/etc; cp /path/to/foobar.conf root/etc/
$ mkdir -p root/usr/bin; cp /path/to/foobar root/usr/bin/

3) Exclude system-owned directories from your RPM's ownership:

$ togo file exclude root/etc root/usr/bin

4) (OPTIONAL) Modify the generated spec to change your package description/dependencies/version/whatever, etc.:

$ vi spec/header

5) Build the RPM:

$ togo build package

-and your RPM is spit out into the ./rpms directory.

Android Studio: Can't start Git

For the one using mac who installed Xcode7, you have to start Xcode and accept the license agreement for the android studio error to go away.

Rails: update_attribute vs update_attributes

Please refer to update_attribute. On clicking show source you will get following code

      # File vendor/rails/activerecord/lib/active_record/base.rb, line 2614
2614:       def update_attribute(name, value)
2615:         send(name.to_s + '=', value)
2616:         save(false)
2617:       end

and now refer update_attributes and look at its code you get

      # File vendor/rails/activerecord/lib/active_record/base.rb, line 2621
2621:       def update_attributes(attributes)
2622:         self.attributes = attributes
2623:         save
2624:       end

the difference between two is update_attribute uses save(false) whereas update_attributes uses save or you can say save(true).

Sorry for the long description but what I want to say is important. save(perform_validation = true), if perform_validation is false it bypasses (skips will be the proper word) all the validations associated with save.

For second question

Also, what is the correct syntax to pass a hash to update_attributes... check out my example at the top.

Your example is correct.

Object.update_attributes(:field1 => "value", :field2 => "value2", :field3 => "value3")


Object.update_attributes :field1 => "value", :field2 => "value2", :field3 => "value3"

or if you get all fields data & name in a hash say params[:user] here use just


If Browser is Internet Explorer: run an alternative script instead

This article is quite explanatory:

If your JS is unobtrusive, you can just use:

<![if !IE]>
   <script src...

Downloading folders from aws s3, cp or sync?

In case you need to use another profile, especially cross account. you need to add the profile in the config file

[profile profileName]
region = us-east-1
role_arn = arn:aws:iam::XXX:role/XXXX
source_profile = default

and then if you are accessing only a single file

aws s3 cp s3://crossAccountBucket/dir localdir --profile profileName

spring autowiring with unique beans: Spring expected single matching bean but found 2

The issue is because you have a bean of type SuggestionService created through @Component annotation and also through the XML config . As explained by JB Nizet, this will lead to the creation of a bean with name 'suggestionService' created via @Component and another with name 'SuggestionService' created through XML .

When you refer SuggestionService by @Autowired, in your controller, Spring autowires "by type" by default and find two beans of type 'SuggestionService'

You could do the following

  1. Remove @Component from your Service and depend on mapping via XML - Easiest

  2. Remove SuggestionService from XML and autowire the dependencies - use util:map to inject the indexSearchers map.

  3. Use @Resource instead of @Autowired to pick the bean by its name .

     private SuggestionService service;


    private SuggestionService service;

both should work.The third is a dirty fix and it's best to resolve the bean conflict through other ways.

How to format a number as percentage in R?

You can use the scales package just for this operation (without loading it with require or library)


Establish a VPN connection in cmd

Have you looked into rasdial?

Just incase anyone wanted to do this and finds this in the future, you can use rasdial.exe from command prompt to connect to a VPN network

ie rasdial "VPN NETWORK NAME" "Username" *

it will then prompt for a password, else you can use "username" "password", this is however less secure

What is the instanceof operator in JavaScript?

On the question "When is it appropriate and when not?", my 2 cents:

instanceof is rarely useful in production code, but useful in tests where you want to assert that your code returns / creates objects of the correct types. By being explicit about the kinds of objects your code is returning / creating, your tests become more powerful as a tool for understanding and documenting your code.

String vs. StringBuilder

A simple example to demonstrate the difference in speed when using String concatenation vs StringBuilder:

System.Diagnostics.Stopwatch time = new Stopwatch();
string test = string.Empty;
for (int i = 0; i < 100000; i++)
    test += i;
System.Console.WriteLine("Using String concatenation: " + time.ElapsedMilliseconds + " milliseconds");


Using String concatenation: 15423 milliseconds

StringBuilder test1 = new StringBuilder();
for (int i = 0; i < 100000; i++)
System.Console.WriteLine("Using StringBuilder: " + time.ElapsedMilliseconds + " milliseconds");


Using StringBuilder: 10 milliseconds

As a result, the first iteration took 15423 ms while the second iteration using StringBuilder took 10 ms.

It looks to me that using StringBuilder is faster, a lot faster.

Jquery how to find an Object by attribute in an Array

I have created a util service for my angular application. It have two function which use very often.

For example you have object.

First getting value from object recursively without throwing undefined error.

{prop: { nestedProp1: {nestedProp2: somevalue}}}; get nestedProp2 2 without undefined checks.

Second filter array on basis

[{prop: { nestedProp1: {nestedProp2: somevalue1}}}, {prop: { nestedProp1: {nestedProp2: somevalue2}}}];

Find object from array with nestedProp2=somevalue2

app.service('UtilService', function(httpService) {
this.mapStringKeyVal = function(map, field) {
    var lastIdentifiedVal = null;
    var parentVal = map;
            lastIdentifiedVal = parentVal[val]; 
            parentVal = parentVal[val]; 
    return lastIdentifiedVal;

this.arrayPropFilter = function(array, field,value) {
    var lastIdentifiedVal = null;
    var mapStringKeyVal = this.mapStringKeyVal;
        var valueFound = mapStringKeyVal(arrayItem,field);
        if(!lastIdentifiedVal  && valueFound && valueFound==value){
            lastIdentifiedVal = arrayItem;
    return lastIdentifiedVal;

For solution for current question. inject UtilService and call,


Or more advanced


SQL update trigger only when column is modified

Whenever a record has updated a record is "deleted". Here is my example:

ALTER TRIGGER [dbo].[UpdatePhyDate]
   ON  [dbo].[M_ContractDT1]
    -- on ContarctDT1 PhyQty is updated 
    -- I want system date in Phytate automatically saved

    declare @dt1ky as int   

        select @dt1ky = dt1ky from deleted

        update M_ContractDT1 set PhyDate=GETDATE() where Dt1Ky=  @dt1ky     



It works fine

Bootstrap 3 Navbar Collapse

The big difference between Bootstrap 2 and Bootstrap 3 is that Bootstrap 3 is "mobile first".

That means the default styles are designed for mobile devices and in the case of Navbars, that means it's "collapsed" by default and "expands" when it reaches a certain minimum size.

Bootstrap 3's site actually has a "hint" as to what to do:

Customize the collapsing point

Depending on the content in your navbar, you might need to change the point at which your navbar switches between collapsed and horizontal mode. Customize the @grid-float-breakpoint variable or add your own media query.

If you're going to re-compile your LESS, you'll find the noted LESS variable in the variables.less file. It's currently set to "expand" @media (min-width: 768px) which is a "small screen" (ie. a tablet) by Bootstrap 3 terms.

@grid-float-breakpoint: @screen-tablet;

If you want to keep the collapsed a little longer you can adjust it like such:

@grid-float-breakpoint: @screen-desktop; (992px break-point)

or expand sooner

@grid-float-breakpoint: @screen-phone (480px break-point)

If you want to have it expand later, and not deal with re-compiling the LESS, you'll have to overwrite the styles that get applied at the 768px media query and have them return to the previous value. Then re-add them at the appropriate time.

I'm not sure if there's a better way to do it. Recompiling the Bootstrap LESS to your needs is the best (easiest) way. Otherwise, you'll have to find all the CSS media queries that affect your Navbar, overwrite them to default styles @ the 768px width and then revert them back at a higher min-width.

Recompiling the LESS will do all that magic for you just by changing the variable. Which is pretty much the point of LESS/SASS pre-compilers. =)

(note, I did look them all up, it's about 100 lines of code, which is annoy enough for me to drop the idea and just re-compile Bootstrap for a given project and avoid messing something up by accident)

I hope that helps!


PHP cURL, extract an XML response


<song dateplayed="2011-07-24 19:40:26">
    <title>I left my heart on Europa</title>
    <artist>Ship of Nomads</artist>
<song dateplayed="2011-07-24 19:27:42">
    <title>Oh Ganymede</title>
<song dateplayed="2011-07-24 19:23:50">
    <artist>Jewitt K. Sheppard</artist>


$mysongs = simplexml_load_file('songs.xml');
echo $mysongs->song[0]->artist;

Output on your browser: Ship of Nomads


mysql select from n last rows

Might be a very late answer, but this is good and simple.

select * from table_name order by id desc limit 5

This query will return a set of last 5 values(last 5 rows) you 've inserted in your table

How do I get the picture size with PIL?

Followings gives dimensions as well as channels:

import numpy as np
from PIL import Image

with as img:
    shape = np.array(img).shape

Why is __init__() always called after __new__()?

Digging little deeper into that!

The type of a generic class in CPython is type and its base class is Object (Unless you explicitly define another base class like a metaclass). The sequence of low level calls can be found here. The first method called is the type_call which then calls tp_new and then tp_init.

The interesting part here is that tp_new will call the Object's (base class) new method object_new which does a tp_alloc (PyType_GenericAlloc) which allocates the memory for the object :)

At that point the object is created in memory and then the __init__ method gets called. If __init__ is not implemented in your class then the object_init gets called and it does nothing :)

Then type_call just returns the object which binds to your variable.

Warning: implode() [function.implode]: Invalid arguments passed

function my_get_tags_sitemap(){
    if ( !function_exists('wp_tag_cloud') || get_option('cb2_noposttags')) return;
    $unlinkTags = get_option('cb2_unlinkTags'); 
    echo '<div class="tags"><h2>Tags</h2>';
    $ret = []; // here you need to add array which you call inside implode function
        $tags = get_tags();
        foreach ($tags as $tag){
            $ret[]= $tag->name;
        echo implode(', ', $ret);
        wp_tag_cloud('separator=, &smallest=11&largest=11');
    echo '</div>';

Check image width and height before upload with Javascript

I agree. Once it is uploaded to somewhere the user's browser can access then it is pretty easy to get the size. As you need to wait for the image to load you'll want to hook into the onload event for img.

var width, height;

var img = document.createElement("img");
img.onload = function() {
    // `naturalWidth`/`naturalHeight` aren't supported on <IE9. Fallback to normal width/height
    // The natural size is the actual image size regardless of rendering.
    // The 'normal' width/height are for the **rendered** size.

    width  = img.naturalWidth  || img.width;
    height = img.naturalHeight || img.height; 

    // Do something with the width and height

// Setting the source makes it start downloading and eventually call `onload`
img.src = "";

Sending an HTTP POST request on iOS

Objective C

Post API with parameters and validate with url to navigate if json
response key with status:"success"

NSString *string= [NSString stringWithFormat:@"url?uname=%@&pass=%@&uname_submit=Login",self.txtUsername.text,self.txtPassword.text];
    NSURL *url = [NSURL URLWithString:string];
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
    [request setHTTPMethod:@"POST"];
    NSURLResponse *response;
    NSError *err;
    NSData *responseData = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&err];
    NSLog(@"responseData: %@", responseData);
    NSString *str = [[NSString alloc] initWithData:responseData encoding:NSUTF8StringEncoding];
    NSLog(@"responseData: %@", str);
        NSDictionary* json = [NSJSONSerialization JSONObjectWithData:responseData
    NSDictionary* latestLoans = [json objectForKey:@"status"];
    NSString *str2=[NSString stringWithFormat:@"%@", latestLoans];
    NSString *str3=@"success";
    if ([str3 isEqualToString:str2 ])
        [self performSegueWithIdentifier:@"move" sender:nil];
        UIAlertController *alert= [UIAlertController
                                 alertControllerWithTitle:@"Try Again"
                                 message:@"Username or Password is Incorrect."
        UIAlertAction* ok = [UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleDefault
                                                   handler:^(UIAlertAction * action){
                                                       [self.view endEditing:YES];
        [alert addAction:ok];
        [[UIView appearanceWhenContainedIn:[UIAlertController class], nil] setTintColor:[UIColor redColor]];
        [self presentViewController:alert animated:YES completion:nil];
        [self.view endEditing:YES];

JSON Response : {"status":"success","user_id":"58","user_name":"dilip","result":"You have been logged in successfully"} Working code


Create space at the beginning of a UITextField

Swift 4, Xcode 9

I like Pheepster's answer, but how about we do it all from the extension, without requiring VC code or any subclassing:

import UIKit

extension UITextField {

    @IBInspectable var paddingLeftCustom: CGFloat {
        get {
            return leftView!.frame.size.width
        set {
            let paddingView = UIView(frame: CGRect(x: 0, y: 0, width: newValue, height: frame.size.height))
            leftView = paddingView
            leftViewMode = .always

    @IBInspectable var paddingRightCustom: CGFloat {
        get {
            return rightView!.frame.size.width
        set {
            let paddingView = UIView(frame: CGRect(x: 0, y: 0, width: newValue, height: frame.size.height))
            rightView = paddingView
            rightViewMode = .always     

Data at the root level is invalid

I found that the example I was using had an xml document specification on the first line. I was using a stylesheet I got at this blog entry and the first line was


which was causing the error. When I removed that line, so that the stylesheet started with the line

<xsl:stylesheet version="1.0" xmlns:DTS="" xmlns:xsl="">

my transform worked. By the way, that blog post was the first good, easy-to follow example I have found for trying to get information from the XML definition of an SSIS package, but I did have to modify the paths in the example for my SSIS 2008 packages, so you might too. I also created a version to extract the "flow" from the precedence constraints. My final one looks like this:

    <xsl:stylesheet version="1.0" xmlns:DTS="" xmlns:xsl="">
    <xsl:output method="text" encoding="utf-8" />
    <xsl:template match="/">
    <xsl:for-each select="//DTS:PrecedenceConstraints/DTS:PrecedenceConstraint">
      <xsl:value-of select="@DTS:From"/>
      <xsl:value-of select="@DTS:To"/>

and gave me a CSV with the tilde as my line delimiter. I replaced that with a line feed in my text editor then imported into excel to get a with look at the data flow in the package.

How to install XCODE in windows 7 platform?

X-code is primarily made for OS-X or iPhone development on Mac systems. Versions for Windows are not available. However this might help!

There is no way to get Xcode on Windows; however you can use a different SDK like Corona instead although it will not use Objective-C (I believe it uses Lua). I have however heard that it is horrible to use.


"Cloning" row or column vectors

import numpy as np


[[ 1.  1.  1.]
 [ 2.  2.  2.]
 [ 3.  3.  3.]]

How can I convert a Unix timestamp to DateTime and vice versa?

DateTime unixEpoch = DateTime.ParseExact("1970-01-01", "yyyy-MM-dd", System.Globalization.CultureInfo.InvariantCulture);
DateTime convertedTime = unixEpoch.AddMilliseconds(unixTimeInMillisconds);

Of course, one can make unixEpoch a global static, so it only needs to appear once in your project, and one can use AddSeconds if the UNIX time is in seconds.

To go the other way:

double unixTimeInMilliseconds = timeToConvert.Subtract(unixEpoch).TotalMilliseconds;

Truncate to Int64 and/or use TotalSeconds as needed.

Using a different font with twitter bootstrap

Hi you can create a customized build on bootstrap, just change the font name in the following pages

Bootstrap 2.3.2

Bootstrap 3

After that, make sure to use proper @font-face in a css file and link that to your page. Or you could use font kit generators.

Preprocessor check if multiple defines are not defined

#if !defined(MANUF) || !defined(SERIAL) || !defined(MODEL)

OkHttp Post Body as JSON

You can create your own JSONObject then toString().

Remember run it in the background thread like doInBackground in AsyncTask.

OkHttp version > 4:

// create your json here
JSONObject jsonObject = new JSONObject();
try {
    jsonObject.put("KEY1", "VALUE1");
    jsonObject.put("KEY2", "VALUE2");
} catch (JSONException e) {

val client = OkHttpClient()
val mediaType = "application/json; charset=utf-8".toMediaType()
val body = jsonObject.toString().toRequestBody(mediaType)
val request: Request = Request.Builder()

var response: Response? = null
try {
    response = client.newCall(request).execute()
    val resStr = response.body!!.string()
} catch (e: IOException) {

OkHttp version 3:

// create your json here
JSONObject jsonObject = new JSONObject();
try {
    jsonObject.put("KEY1", "VALUE1");
    jsonObject.put("KEY2", "VALUE2");
} catch (JSONException e) {

  OkHttpClient client = new OkHttpClient();
  MediaType JSON = MediaType.parse("application/json; charset=utf-8");
  // put your json here
  RequestBody body = RequestBody.create(JSON, jsonObject.toString());
  Request request = new Request.Builder()

  Response response = null;
  try {
      response = client.newCall(request).execute();
      String resStr = response.body().string();
  } catch (IOException e) {

Create a function with optional call variables

I don't think your question is very clear, this code assumes that if you're going to include the -domain parameter, it's always 'named' (i.e. dostuff computername arg2 -domain domain); this also makes the computername parameter mandatory.

Function DoStuff(){
        $domain = 'domain1'
    write-host $domain
        write-host "arg2 present... executing script block"
        write-host "arg2 missing... exiting or whatever"

node.js - how to write an array to file

We can simply write the array data to the filesystem but this will raise one error in which ',' will be appended to the end of the file. To handle this below code can be used:

var fs = require('fs');

var file = fs.createWriteStream('hello.txt');
file.on('error', function(err) { Console.log(err) });
data.forEach(value => file.write(`${value}\r\n`));


is used for the new Line.


won't help. Please refer this

Inserting values into tables Oracle SQL

You can insert into a table from a SELECT.

  Employee (emp_id, emp_name, emp_address, emp_state, emp_position, emp_manager)
  'John Doe',
  '1 River Walk, Green Street',
  (SELECT id FROM state WHERE name = 'New York'),
  (SELECT id FROM positions WHERE name = 'Sales Executive'),
  (SELECT id FROM manager WHERE name = 'Barry Green')

Or, similarly...

  Employee (emp_id, emp_name, emp_address, emp_state, emp_position, emp_manager)
  'John Doe',
  '1 River Walk, Green Street',,,
WHERE     = 'New York'
  AND = 'Sales Executive'
  AND   = 'Barry Green'

Though this one does assume that all the look-ups exist. If, for example, there is no position name 'Sales Executive', nothing would get inserted with this version.

Python handling socket.error: [Errno 104] Connection reset by peer

You can try to add some time.sleep calls to your code.

It seems like the server side limits the amount of requests per timeunit (hour, day, second) as a security issue. You need to guess how many (maybe using another script with a counter?) and adjust your script to not surpass this limit.

In order to avoid your code from crashing, try to catch this error with try .. except around the urllib2 calls.

Select mySQL based only on month and year

you can do it by changing $q to this:

$q="SELECT * FROM projects WHERE YEAR(date) = $year_v AND MONTH(date) = $month_v;

Bad Request, Your browser sent a request that this server could not understand

If you use Apache httpd web server in version above 2.2.15-60, then it could be also because of underscore _ in hostname.

how do I create an infinite loop in JavaScript

By omitting all parts of the head, the loop can also become infinite:

for (;;) {}

How do I temporarily disable triggers in PostgreSQL?

You can also disable triggers in pgAdmin (III):

  1. Find your table
  2. Expand the +
  3. Find your trigger in Triggers
  4. Right-click, uncheck "Trigger Enabled?"

How to create a list of objects?

The Python Tutorial discusses how to use lists.

Storing a list of classes is no different than storing any other objects.

def MyClass(object):

my_types = [str, int, float, MyClass]

how to make a whole row in a table clickable as a link?

I've invested a lot of time trying to solve this problem.

There are 3 approaches:

  1. Use JavaScript. The clear drawbacks: it's not possible to open a new tab natively, and when hovering over the row there will be no indication on status bar like regular links have. Accessibility is also a question.

  2. Use HTML/CSS only. This means putting <a> nested under each <td>. A simple approach like this fiddle doesn't work - Because the clickable surface is not necessarily equal for each column. This is a serious UX concern. Also, if you need a <button> on the row, it is not valid HTML to nest it under <a> tag (although browsers are ok with that).

    I've found 3 other ways to implement this approach. First is ok, the other two are not great.

    a) Have a look on this example:

    tr {
      height: 0;
    td {
      height: 0;
      padding: 0;
    /* A hack to overcome differences between Chrome and Firefox */
    @-moz-document url-prefix() {
      td {
        height: 100%;
    a {
      display: block;
      height: 100%;

    It works, but due to inconsistencies between Chrome and Firefox it requires browser-specific hack to overcome the differences. Also Chrome will always align the cell content to the top, which can cause problems with long texts, especially if varying line heights are involved.

    b) Setting <td> to { display: contents; }. This leads to 2 other problems:

    b1. If someone else tries to style directly the <td> tag, like setting it to { width: 20px; }, we need to pass that style somehow to the <a> tag. We need some magic to do that, probably more magic than in the Javascript alternative.

    b2. { display: contents; } is still experimental; specifically it's not supported on Edge.

    c) Setting <td> to { height: --some-fixed-value; }. This is just not flexible enough.

  3. The last approach, which I recommend to seriously thinking of, is to not using clickable rows at all. Clickable rows is not a great UX experience: it's not easy to visually mark them as clickable, and it poses challenges when multiple parts are clickable within the rows, like buttons. So a viable alternative could be to have an <a> tag only on the first column, displayed as a regular link, and give it the role of navigating the whole row.

Get last n lines of a file, similar to tail

I found the Popen above to be the best solution. It's quick and dirty and it works For python 2.6 on Unix machine i used the following

def GetLastNLines(self, n, fileName):
    Name:           Get LastNLines
    Description:        Gets last n lines using Unix tail
    Output:         returns last n lines of a file
    Keyword argument:
    n -- number of last lines to return
    filename -- Name of the file you need to tail into
    p = subprocess.Popen(['tail','-n',str(n),self.__fileName], stdout=subprocess.PIPE)
    soutput, sinput = p.communicate()
    return soutput

soutput will have will contain last n lines of the code. to iterate through soutput line by line do:

for line in GetLastNLines(50,'myfile.log').split('\n'):
    print line