Programs & Examples On #Amalgamation

Improve INSERT-per-second performance of SQLite

Several tips:

  1. Put inserts/updates in a transaction.
  2. For older versions of SQLite - Consider a less paranoid journal mode (pragma journal_mode). There is NORMAL, and then there is OFF, which can significantly increase insert speed if you're not too worried about the database possibly getting corrupted if the OS crashes. If your application crashes the data should be fine. Note that in newer versions, the OFF/MEMORY settings are not safe for application level crashes.
  3. Playing with page sizes makes a difference as well (PRAGMA page_size). Having larger page sizes can make reads and writes go a bit faster as larger pages are held in memory. Note that more memory will be used for your database.
  4. If you have indices, consider calling CREATE INDEX after doing all your inserts. This is significantly faster than creating the index and then doing your inserts.
  5. You have to be quite careful if you have concurrent access to SQLite, as the whole database is locked when writes are done, and although multiple readers are possible, writes will be locked out. This has been improved somewhat with the addition of a WAL in newer SQLite versions.
  6. Take advantage of saving space...smaller databases go faster. For instance, if you have key value pairs, try making the key an INTEGER PRIMARY KEY if possible, which will replace the implied unique row number column in the table.
  7. If you are using multiple threads, you can try using the shared page cache, which will allow loaded pages to be shared between threads, which can avoid expensive I/O calls.
  8. Don't use !feof(file)!

I've also asked similar questions here and here.

Convert string to JSON array

if the response is like this

"GetDataResult": "[{\"UserID\":1,\"DeviceID\":\"d1254\",\"MobileNO\":\"056688\",\"Pak1\":true,\"pak2\":true,\"pak3\":false,\"pak4\":true,\"pak5\":true,\"pak6\":false,\"pak7\":false,\"pak8\":true,\"pak9\":false,\"pak10\":true,\"pak11\":false,\"pak12\":false}]"

you can parse like this

JSONObject jobj=new JSONObject(response);
        String c = jobj.getString("GetDataResult");         
        JSONArray jArray = new JSONArray(c);

here the JsonArray size is 1.Otherwise you should use for loop for getting values.

jQuery bind to Paste Event, how to get the content of the paste

It would appear as though this event has some clipboardData property attached to it (it may be nested within the originalEvent property). The clipboardData contains an array of items and each one of those items has a getAsString() function that you can call. This returns the string representation of what is in the item.

Those items also have a getAsFile() function, as well as some others which are browser specific (e.g. in webkit browsers, there is a webkitGetAsEntry() function).

For my purposes, I needed the string value of what is being pasted. So, I did something similar to this:

$(element).bind("paste", function (e) {
    e.originalEvent.clipboardData.items[0].getAsString(function (pStringRepresentation) {
        // pStringRepresentation now contains the string representation of what was pasted.
        // This does not include HTML or any markup. Essentially jQuery's $(element).text()
        // function result.

You'll want to perform an iteration through the items, keeping a string concatenation result.

The fact that there is an array of items makes me think more work will need to be done, analyzing each item. You'll also want to do some null/value checks.

Python 3 Building an array of bytes

I think Scapy is what are you looking for.

you can build and send frames (packets) with it

How do I view the full content of a text or varchar(MAX) column in SQL Server 2008 Management Studio?

It sounds like the Xml may not be well formed. If that is the case, then you will not be able to cast it as Xml and given that, you are limited in how much text you can return in Management Studio. However, you could break up the text into smaller chunks like so:

With Tally As
        Select ROW_NUMBER() OVER ( ORDER BY s1.object_id ) - 1 As Num
        From sys.sysobjects As s1
            Cross Join sys.sysobjects As s2
Select Substring(T1.textCol, T2.Num * 8000 + 1, 8000)
From Table As T1
    Cross Join Tally As T2
Where T2.Num <= Ceiling(Len(T1.textCol) / 8000)
Order By T2.Num

You would then need to manually combine them again.


It sounds like there are some characters in the text data that the Xml parser does not like. You could try converting those values to entities and then try the Convert(xml, data) trick. So something like:

Update Table
Set Data = Replace(Cast(Data As varchar(max)),'<','&lt;')

(I needed to cast to varchar(max) because the replace function will not work on text columns. There should not be any reason you couldn't convert those text columns to varchar(max).)

Jupyter/IPython Notebooks: Shortcut for "run all"?

As of 5.5 you can run Kernel > Restart and Run All

Select from where field not equal to Mysql Php

You can use also

select * from tablename where column1 ='a' and column2!='b';


MySql: Tinyint (2) vs tinyint(1) - what is the difference?

About the INT, TINYINT... These are different data types, INT is 4-byte number, TINYINT is 1-byte number. More information here - INTEGER, INT, SMALLINT, TINYINT, MEDIUMINT, BIGINT.

The syntax of TINYINT data type is TINYINT(M), where M indicates the maximum display width (used only if your MySQL client supports it).

Numeric Type Attributes.

How to build x86 and/or x64 on Windows from command line with CMAKE?

Besides CMAKE_GENERATOR_PLATFORM variable, there is also the -A switch

cmake -G "Visual Studio 16 2019" -A Win32
cmake -G "Visual Studio 16 2019" -A x64

  -A <platform-name>           = Specify platform name if supported by

How to convert data.frame column from Factor to numeric

From ?factor:

To transform a factor f to approximately its original numeric values, as.numeric(levels(f))[f] is recommended and slightly more efficient than as.numeric(as.character(f)).

How to scroll page in flutter

Use LayoutBuilder and Get the output you want

Wrap the SingleChildScrollView with LayoutBuilder and implement the Builder function.

we can use a LayoutBuilder to get the box contains or the amount of space available.

    builder: (BuildContext context, BoxConstraints constraints){
      return SingleChildScrollView(
        child: Stack(
          children: <Widget>[
              height: constraints.maxHeight,

Writing numerical values on the plot with Matplotlib

You can use the annotate command to place text annotations at any x and y values you want. To place them exactly at the data points you could do this

import numpy
from matplotlib import pyplot

x = numpy.arange(10)
y = numpy.array([5,3,4,2,7,5,4,6,3,2])

fig = pyplot.figure()
ax = fig.add_subplot(111)
for i,j in zip(x,y):

If you want the annotations offset a little, you could change the annotate line to something like


PHP: cannot declare class because the name is already in use

you want to use include_once() or require_once(). The other option would be to create an additional file with all your class includes in the correct order so they don't need to call includes themselves:


include 'database.php';
include 'parent.php';
include 'child1.php';
include 'child2.php';

Then you just need:


How to get current route in Symfony 2?

I think this is the easiest way to do this:

class MyController extends Controller
    public function myAction($_route)


How to format a date using ng-model?

Here is very handy directive angular-datetime. You can use it like this:

<input type="text" datetime="yyyy-MM-dd HH:mm:ss" ng-model="myDate">

It also add mask to your input and perform validation.

Sass nth-child nesting

You're trying to do &(2), &(4) which won't work

#romtest {
  .detailed {
    th {
      &:nth-child(2) {//your styles here}
      &:nth-child(4) {//your styles here}
      &:nth-child(6) {//your styles here}

Ionic android build Error - Failed to find 'ANDROID_HOME' environment variable

To add ANDROID_HOME value permanently,

gedit ~/.bashrc

and add the following lines

export ANDROID_HOME=/root/Android/Sdk

Save the file and you need not update ANDROID_HOME value everytime.

Adding iOS UITableView HeaderView (not section header)

- (UIView *)tableView:(UITableView *)tableView viewForHeaderInSection:(NSInteger)section

    UIView *headerView = [[UIView alloc] initWithFrame:CGRectMake(0,0,tableView.frame.size.width,30)];
    headerView.backgroundColor=[[UIColor redColor]colorWithAlphaComponent:0.5f];
    headerView.layer.borderColor=[UIColor blackColor].CGColor;

    UILabel *headerLabel = [[UILabel alloc] initWithFrame:CGRectMake(10, 5,100,20)];

    headerLabel.textAlignment = NSTextAlignmentRight;
    headerLabel.text = @"LeadCode ";
    //headerLabel.textColor=[UIColor whiteColor];
    headerLabel.backgroundColor = [UIColor clearColor];

    [headerView addSubview:headerLabel];

    UILabel *headerLabel1 = [[UILabel alloc] initWithFrame:CGRectMake(60, 0, headerView.frame.size.width-120.0, headerView.frame.size.height)];

    headerLabel1.textAlignment = NSTextAlignmentRight;
    headerLabel1.text = @"LeadName";
    headerLabel.textColor=[UIColor whiteColor];
    headerLabel1.backgroundColor = [UIColor clearColor];

    [headerView addSubview:headerLabel1];

    return headerView;


How to disable manual input for JQuery UI Datepicker field?

When you make the input, set it to be readonly.

<input type="text" name="datepicker" id="datepicker" readonly="readonly" />

Sequelize, convert entity to plain object

you can use the query options {raw: true} to return the raw result. Your query should like follows:

  where: {
    nodeid: node.nodeid
  raw: true,

also if you have associations with include that gets flattened. So, we can use another parameter nest:true

  where: {
    nodeid: node.nodeid
  raw: true,
  nest: true,

How to know if a DateTime is between a DateRange in C#

Usually I create Fowler's Range implementation for such things.

public interface IRange<T>
    T Start { get; }
    T End { get; }
    bool Includes(T value);
    bool Includes(IRange<T> range);

public class DateRange : IRange<DateTime>         
    public DateRange(DateTime start, DateTime end)
        Start = start;
        End = end;

    public DateTime Start { get; private set; }
    public DateTime End { get; private set; }

    public bool Includes(DateTime value)
        return (Start <= value) && (value <= End);

    public bool Includes(IRange<DateTime> range)
        return (Start <= range.Start) && (range.End <= End);

Usage is pretty simple:

DateRange range = new DateRange(startDate, endDate);

Update TextView Every Second

If you want to show time on textview then better use Chronometer or TextClock

Using Chronometer:This was added in API 1. It has lot of option to customize it.

Your xml

    android:textSize="30sp" />

Your activity

Chronometer mChronometer=(Chronometer) findViewById(;

Using TextClock: This widget is introduced in API level 17. I personally like Chronometer.

Your xml

    android:format12Hour="hh:mm:ss a"
    android:textStyle="bold" />

Thats it, you are done.

You can use any of these two widgets. This will make your life easy.

How to get an MD5 checksum in PowerShell

Here's a function I use that handles relative and absolute paths:

function md5hash($path)
    $fullPath = Resolve-Path $path
    $md5 = new-object -TypeName System.Security.Cryptography.MD5CryptoServiceProvider
    $file = [System.IO.File]::Open($fullPath,[System.IO.Filemode]::Open, [System.IO.FileAccess]::Read)
    try {
    } finally {

Thanks to @davor above for the suggestion to use Open() instead of ReadAllBytes() and to @jpmc26 for the suggestion to use a finally block.

how to remove multiple columns in r dataframe?

Basic subsetting:

album2 <- album2[, -5] #delete column 5
album2 <- album2[, -c(5:7)] # delete columns 5 through 7

System.Windows.Markup.XamlParseException' occurred in PresentationFramework.dll?

When I had this problem, I had literally just forgot to fill in a parameter value in the XAML of the code.

For some reason though, the exception would send me to the CS of the WPF program rather than the XAML. No idea why.

How to install pip in CentOS 7?

curl | python3.4

Or if you don't have curl for some reason:


After this you should be able to run

$ pip3

How to use global variables in React Native?

The way you should be doing it in React Native (as I understand it), is by saving your 'global' variable in your index.js, for example. From there you can then pass it down using props.


    class MainComponent extends Component {

        componentDidMount() {
            //Define some variable in your component
            this.variable = "What's up, I'm a variable";
        render () {
                renderScene={(() => {
                                //Pass the variable you want to be global through here

    class SceneComponent extends Component {

        render() {


How to change font size in a textbox in html

For a <input type='text'> element:

input { font-size: 18px; }

or for a <textarea>:

textarea { font-size: 18px; }

or for a <select>:

select { font-size: 18px; }

you get the drift.

Found shared references to a collection org.hibernate.HibernateException

I too got the same issue, someone used BeanUtils.copyProperties(source, target). Here both source and target, are using the same collection as attribute.

So i just used the deep copy as below..

How to Clone Collection in Java - Deep copy of ArrayList and HashSet

When do I need to use Begin / End Blocks and the Go keyword in SQL Server?

GO is like the end of a script.

You could have multiple CREATE TABLE statements, separated by GO. It's a way of isolating one part of the script from another, but submitting it all in one block.

BEGIN and END are just like { and } in C/++/#, Java, etc.

They bound a logical block of code. I tend to use BEGIN and END at the start and end of a stored procedure, but it's not strictly necessary there. Where it IS necessary is for loops, and IF statements, etc, where you need more then one step...

IF EXISTS (SELECT * FROM my_table WHERE id = @id)
   INSERT INTO Log SELECT @id, 'deleted'
   DELETE my_table WHERE id = @id

How to split a string in two and store it in a field

I would suggest the following:

String[] parsedInput = str.split("\n"); String firstName = parsedInput[0].split(": ")[1]; String lastName = parsedInput[1].split(": ")[1]; myMap.put(firstName,lastName); 

Why do we have to specify FromBody and FromUri?

When a parameter has [FromBody], Web API uses the Content-Type header to select a formatter. In this example, the content type is "application/json" and the request body is a raw JSON string (not a JSON object).

At most one parameter is allowed to read from the message body. So this will not work:

// Caution: Will not work!    
public HttpResponseMessage Post([FromBody] int id, [FromBody] string name) { ... }

The reason for this rule is that the request body might be stored in a non-buffered stream that can only be read once.

Please go through the website for more details:

Set background color in PHP?

This really depends on what you need to do. If you want to set a background colour on a page then you need to use CSS as per Jay's and David Dorward's answers.

If you are building an image with PHP then you can use the GD library to allocate colours yourself. I don't recommend this without thoroughly reading up on how to create images with GD.

Python - 'ascii' codec can't decode byte

You use u"??".encode('utf8') to encode an unicode string. But if you want to represent "??", you should decode it. Just like:


You will get what you want. Maybe you should learn more about encode & decode.

DataGridView changing cell background color

Similar as shown and mentioned:

Notes: Take into consideration that Cells will change their color (only) after the DataGridView Control is Visible. Therefore one practical solution would be using the:

VisibleChanged Event

In case you wish to keep your style when creating new Rows; also subscribe the:

RowsAdded Event

Example bellow:

///<summary> Instantiate the DataGridView Control. </summary>
private DataGridView dgView = new DataGridView;

///<summary> Method to configure DataGridView Control. </summary>
private void DataGridView_Configuration()
    // In this case the method just contains the VisibleChanged event subscription.

    dgView.VisibleChanged += DgView_VisibleChanged;

    // Uncomment line bellow in case you want to keep the style when creating new rows.
    // dgView.RowsAdded += DgView_RowsAdded;

///<summary> The actual Method that will re-design (Paint) DataGridView Cells. </summary>
 private void DataGridView_PaintCells()
     int nrRows = dgView.Rows.Count;
     int nrColumns = dgView.Columns.Count;
     Color green = Color.LimeGreen;

     // Iterate over the total number of Rows
     for (int row = 0; row < nrRows; row++)
         // Iterate over the total number of Columns
         for (int col = 0; col < nrColumns; col++) 
             // Paint cell location (column, row)
             dgView[col, row].Style.BackColor = green;

///<summary> The DataGridView VisibleChanged Event. </summary>
private void DataGridView_VisibleChanged(object sender, EventArgs e)

/// <summary> Occurrs when a new Row is Created. </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void DataGridView_RowsAdded(object sender, DataGridViewRowsAddedEventArgs e)

Finally: Just call the DataGridView_Configuration() (method)
i.e: Form Load Event.

How to get object size in memory?

Unmanaged object:

  • Marshal.SizeOf(object yourObj);

Value Types:

  • sizeof(object val)

Managed object:

Where can I find free WPF controls and control templates?

Syncfusion has a free community version available with over 650 controls.


You will find an FAQ there with any licensing questions you may have, it sound great to be honest. Have fun!

Edit: The WPF controls themselves are 100+, the number of 650+ refers to all controls for all areas (WPF, Windows Forms etc).

Is div inside list allowed?

If you look at xhtml1-strict.dtd, you'll see

<!ELEMENT li %Flow;>
<!ENTITY % Flow "(#PCDATA | %block; | form | %inline; | %misc;)*">
<!ENTITY % block
     "p | %heading; | div | %lists; | %blocktext; | fieldset | table">

Thus div, p etc. can be inside li (according to XHTML 1.0 Strict DTD from

How do I specify a password to 'psql' non-interactively?

If its not too late to add most of the options in one answer:

There are a couple of options:

  1. set it in the pgpass file. link
  1. set an environment variable and get it from there:

    export PGPASSWORD='password'

and then run your psql to login or even run the command from there:

 psql -h clustername -U username -d testdb
  1. On windows you will have to use "set" :

    set PGPASSWORD=pass and then login to the psql bash.

Import-CSV and Foreach

Solution is to change Delimiter.

Content of the csv file -> Note .. Also space and , in value

Values are 6 Dutch word aap,noot,mies,Piet, Gijs, Jan


a,ap;noo,t;mi es

P,iet;G ,ijs;Ja ,n

$csv = Import-Csv C:\TejaCopy.csv -Delimiter ';' 


Write-Host $csv
@{Col1=a,ap; Col2=noo,t; Col3=mi es} @{Col1=P,iet; Col2=G ,ijs; Col3=Ja ,n}

It is possible to read a CSV file and use other Delimiter to separate each column.

It worked for my script :-)

How to Remove Line Break in String

Private Sub Form_Load()
    Dim s As String

    s = "test" & vbCrLf & "this" & vbCrLf & vbCrLf
    Debug.Print (s & Len(s))

    s = Left(s, Len(s) - Len(vbCrLf))
    Debug.Print (s & Len(s))
End Sub

Static Block in Java

yes, static block is used for initialize the code and it will load at the time JVM start for execution.

static block is used in previous versions of java but in latest version it doesn't work.

Get sum of MySQL column in PHP

$result=mysql_query("SELECT SUM(column) AS total_value FROM table name WHERE column='value'");

Foreach loop in java for a custom object list

If this code fails to operate on every item in the list, it must be because something is throwing an exception before you have completed the list; the likeliest candidate is the method called "insertOrThrow". You could wrap that call in a try-catch structure to handle the exception for whichever items are failing without exiting the loop and the method prematurely.

Changing the space between each item in Bootstrap navbar

Just remember that modifying the padding or margins on any bootstrap grid elements is likely to create overflowing elements at some point at lower screen-widths.

If that happens just remember to use CSS media queries and only include the margins at screen-widths that can handle it.

In keeping with the mobile-first approach of the framework you are working within (bootstrap) it is better to add the padding at widths which can handle it, rather than excluding it at widths which can't.

@media (min-width: 992px){
    .navbar li {
        margin-left : 1em;
        margin-right : 1em;

ExecuteReader requires an open and available Connection. The connection's current state is Connecting

Sorry for only commenting in the first place, but i'm posting almost every day a similar comment since many people think that it would be smart to encapsulate ADO.NET functionality into a DB-Class(me too 10 years ago). Mostly they decide to use static/shared objects since it seems to be faster than to create a new object for any action.

That is neither a good idea in terms of peformance nor in terms of fail-safety.

Don't poach on the Connection-Pool's territory

There's a good reason why ADO.NET internally manages the underlying Connections to the DBMS in the ADO-NET Connection-Pool:

In practice, most applications use only one or a few different configurations for connections. This means that during application execution, many identical connections will be repeatedly opened and closed. To minimize the cost of opening connections, ADO.NET uses an optimization technique called connection pooling.

Connection pooling reduces the number of times that new connections must be opened. The pooler maintains ownership of the physical connection. It manages connections by keeping alive a set of active connections for each given connection configuration. Whenever a user calls Open on a connection, the pooler looks for an available connection in the pool. If a pooled connection is available, it returns it to the caller instead of opening a new connection. When the application calls Close on the connection, the pooler returns it to the pooled set of active connections instead of closing it. Once the connection is returned to the pool, it is ready to be reused on the next Open call.

So obviously there's no reason to avoid creating,opening or closing connections since actually they aren't created,opened and closed at all. This is "only" a flag for the connection pool to know when a connection can be reused or not. But it's a very important flag, because if a connection is "in use"(the connection pool assumes), a new physical connection must be openend to the DBMS what is very expensive.

So you're gaining no performance improvement but the opposite. If the maximum pool size specified (100 is the default) is reached, you would even get exceptions(too many open connections ...). So this will not only impact the performance tremendously but also be a source for nasty errors and (without using Transactions) a data-dumping-area.

If you're even using static connections you're creating a lock for every thread trying to access this object. ASP.NET is a multithreading environment by nature. So theres a great chance for these locks which causes performance issues at best. Actually sooner or later you'll get many different exceptions(like your ExecuteReader requires an open and available Connection).


  • Don't reuse connections or any ADO.NET objects at all.
  • Don't make them static/shared(in VB.NET)
  • Always create, open(in case of Connections), use, close and dispose them where you need them(f.e. in a method)
  • use the using-statement to dispose and close(in case of Connections) implicitely

That's true not only for Connections(although most noticable). Every object implementing IDisposable should be disposed(simplest by using-statement), all the more in the System.Data.SqlClient namespace.

All the above speaks against a custom DB-Class which encapsulates and reuse all objects. That's the reason why i commented to trash it. That's only a problem source.

Edit: Here's a possible implementation of your retrievePromotion-method:

public Promotion retrievePromotion(int promotionID)
    Promotion promo = null;
    var connectionString = System.Configuration.ConfigurationManager.ConnectionStrings["MainConnStr"].ConnectionString;
    using (SqlConnection connection = new SqlConnection(connectionString))
        var queryString = "SELECT PromotionID, PromotionTitle, PromotionURL FROM Promotion WHERE PromotionID=@PromotionID";
        using (var da = new SqlDataAdapter(queryString, connection))
            // you could also use a SqlDataReader instead
            // note that a DataTable does not need to be disposed since it does not implement IDisposable
            var tblPromotion = new DataTable();
            // avoid SQL-Injection
            da.SelectCommand.Parameters.Add("@PromotionID", SqlDbType.Int);
            da.SelectCommand.Parameters["@PromotionID"].Value = promotionID;
                connection.Open(); // not necessarily needed in this case because DataAdapter.Fill does it otherwise 
                if (tblPromotion.Rows.Count != 0)
                    var promoRow = tblPromotion.Rows[0];
                    promo = new Promotion()
                        promotionID    = promotionID,
                        promotionTitle = promoRow.Field<String>("PromotionTitle"),
                        promotionUrl   = promoRow.Field<String>("PromotionURL")
            catch (Exception ex)
                // log this exception or throw it up the StackTrace
                // we do not need a finally-block to close the connection since it will be closed implicitely in an using-statement
    return promo;

Safely remove migration In Laravel

DO NOT run php artisan migrate:fresh that's gonna drop all the tables

How to remove all callbacks from a Handler?

For any specific Runnable instance, call Handler.removeCallbacks(). Note that it uses the Runnable instance itself to determine which callbacks to unregister, so if you are creating a new instance each time a post is made, you need to make sure you have references to the exact Runnable to cancel. Example:

Handler myHandler = new Handler();
Runnable myRunnable = new Runnable() {
    public void run() {
        //Some interesting task

You can call myHandler.postDelayed(myRunnable, x) to post another callback to the message queue at other places in your code, and remove all pending callbacks with myHandler.removeCallbacks(myRunnable)

Unfortunately, you cannot simply "clear" the entire MessageQueue for a Handler, even if you make a request for the MessageQueue object associated with it because the methods for adding and removing items are package protected (only classes within the android.os package can call them). You may have to create a thin Handler subclass to manage a list of Runnables as they are posted/executed...or look at another paradigm for passing your messages between each Activity

Hope that Helps!

SOAP vs REST (differences)

REST vs SOAP is not the right question to ask.

REST, unlike SOAP is not a protocol.

REST is an architectural style and a design for network-based software architectures.

REST concepts are referred to as resources. A representation of a resource must be stateless. It is represented via some media type. Some examples of media types include XML, JSON, and RDF. Resources are manipulated by components. Components request and manipulate resources via a standard uniform interface. In the case of HTTP, this interface consists of standard HTTP ops e.g. GET, PUT, POST, DELETE.

@Abdulaziz's question does illuminate the fact that REST and HTTP are often used in tandem. This is primarily due to the simplicity of HTTP and its very natural mapping to RESTful principles.

Fundamental REST Principles

Client-Server Communication

Client-server architectures have a very distinct separation of concerns. All applications built in the RESTful style must also be client-server in principle.


Each client request to the server requires that its state be fully represented. The server must be able to completely understand the client request without using any server context or server session state. It follows that all state must be kept on the client.


Cache constraints may be used, thus enabling response data to be marked as cacheable or not-cacheable. Any data marked as cacheable may be reused as the response to the same subsequent request.

Uniform Interface

All components must interact through a single uniform interface. Because all component interaction occurs via this interface, interaction with different services is very simple. The interface is the same! This also means that implementation changes can be made in isolation. Such changes, will not affect fundamental component interaction because the uniform interface is always unchanged. One disadvantage is that you are stuck with the interface. If an optimization could be provided to a specific service by changing the interface, you are out of luck as REST prohibits this. On the bright side, however, REST is optimized for the web, hence incredible popularity of REST over HTTP!

The above concepts represent defining characteristics of REST and differentiate the REST architecture from other architectures like web services. It is useful to note that a REST service is a web service, but a web service is not necessarily a REST service.

See this blog post on REST Design Principles for more details on REST and the above stated bullets.

EDIT: update content based on comments

Set a form's action attribute when submitting?

There's a simple way to do this if you only need to support modern browsers: on your submit button, add a formaction="/alternate/submit/url" attribute like so:

    <input type="submit" value="Submit to a" formaction="/submit/a">
    <input type="submit" value="submit to b" formaction="/submit/b">

It also works on <button> tags.

The gotcha is that old versions of IE (<10) and the Android Browser (<4.0) do not support it. So, if you need to support older browsers, then the existing JS answers will probably work better for you.

More info:

Getting reference to child component in parent component

You may actually go with ViewChild API...


<button (click)="clicked()">click</button>

export class App {
  @ViewChild(Child) vc:Child;
  constructor() { = 'Angular2'

  func(e) {



export class Child implements OnInit{

  onInitialized = new EventEmitter<Child>();
     console.log('called by vc')

Time complexity of nested for-loop

A quick way to explain this is to visualize it.

if both i and j are from 0 to N, it's easy to see O(N^2)


in this case, it's:


This comes out to be 1/2 of N^2, which is still O(N^2)

Convert byte to string in Java

String str = "0x63";
int temp = Integer.parseInt(str.substring(2, 4), 16);
char c = (char)temp;

++i or i++ in for loops ??

No compiler worth its weight in salt will run differently between

for(int i=0; i<10; i++)


for(int i=0;i<10;++i)

++i and i++ have the same cost. The only thing that differs is that the return value of ++i is i+1 whereas the return value of i++ is i.

So for those prefering ++i, there's probably no valid justification, just personal preference.

EDIT: This is wrong for classes, as said in about every other post. i++ will generate a copy if i is a class.

How to get the excel file name / path in VBA

If you need path only this is the most straightforward way:

PathOnly = ThisWorkbook.Path

How can I make the contents of a fixed element scrollable only when it exceeds the height of the viewport?

Here is the pure HTML and CSS solution.

  1. We create a container box for navbar with position: fixed; height:100%;

  2. Then we create an inner box with height: 100%; overflow-y: scroll;

  3. Next, we put out content inside that box.

Here is the code:

        position: fixed;_x000D_
        border: 1px solid #0a2b1d;_x000D_
        width: 200px;_x000D_
        height: 100%;_x000D_
        overflow-y: scroll;_x000D_
        border: 1px solid #0A246A;_x000D_
        border: 3px solid chartreuse;_x000D_
    .content-box p{_x000D_
<div class="nav-box">_x000D_
  <div class="inner-box">_x000D_
    <div class="tabs"><p>Navbar content Start</p></div>_x000D_
    <div class="tabs"><p>Navbar content</p></div>_x000D_
    <div class="tabs"><p>Navbar content</p></div>_x000D_
    <div class="tabs"><p>Navbar content</p></div>_x000D_
    <div class="tabs"><p>Navbar content</p></div>_x000D_
    <div class="tabs"><p>Navbar content</p></div>_x000D_
    <div class="tabs"><p>Navbar content</p></div>_x000D_
    <div class="tabs"><p>Navbar content</p></div>_x000D_
    <div class="tabs"><p>Navbar content</p></div>_x000D_
    <div class="tabs"><p>Navbar content</p></div>_x000D_
    <div class="tabs"><p>Navbar content</p></div>_x000D_
    <div class="tabs"><p>Navbar content End</p></div>_x000D_
<div class="content-box">_x000D_
  <p>Lorem Ipsum</p>_x000D_
  <p>Lorem Ipsum</p>_x000D_
  <p>Lorem Ipsum</p>_x000D_
  <p>Lorem Ipsum</p>_x000D_
  <p>Lorem Ipsum</p>_x000D_
  <p>Lorem Ipsum</p>_x000D_
  <p>Lorem Ipsum</p>_x000D_
  <p>Lorem Ipsum</p>_x000D_
  <p>Lorem Ipsum</p>_x000D_
  <p>Lorem Ipsum</p>_x000D_
  <p>Lorem Ipsum</p>_x000D_
  <p>Lorem Ipsum</p>_x000D_

Link to jsFiddle:

Simple Digit Recognition OCR in OpenCV-Python

OCR which stands for Optical Character Recognition is a computer vision technique used to identify the different types of handwritten digits that are used in common mathematics. To perform OCR in OpenCV we will use the KNN algorithm which detects the nearest k neighbors of a particular data point and then classifies that data point based on the class type detected for n neighbors.

Data Used

This data contains 5000 handwritten digits where there are 500 digits for every type of digit. Each digit is of 20×20 pixel dimensions. We will split the data such that 250 digits are for training and 250 digits are for testing for every class.

Below is the implementation.

import numpy as np
import cv2
# Read the image
image = cv2.imread('digits.png')
# gray scale conversion
gray_img = cv2.cvtColor(image,
# We will divide the image
# into 5000 small dimensions 
# of size 20x20
divisions = list(np.hsplit(i,100) for i in np.vsplit(gray_img,50))
# Convert into Numpy array
# of size (50,100,20,20)
NP_array = np.array(divisions)
# Preparing train_data
# and test_data.
# Size will be (2500,20x20)
train_data = NP_array[:,:50].reshape(-1,400).astype(np.float32)
# Size will be (2500,20x20)
test_data = NP_array[:,50:100].reshape(-1,400).astype(np.float32)
# Create 10 different labels 
# for each type of digit
k = np.arange(10)
train_labels = np.repeat(k,250)[:,np.newaxis]
test_labels = np.repeat(k,250)[:,np.newaxis]
# Initiate kNN classifier
knn =
# perform training of data
# obtain the output from the
# classifier by specifying the
# number of neighbors.
ret, output ,neighbours,
distance = knn.findNearest(test_data, k = 3)
# Check the performance and
# accuracy of the classifier.
# Compare the output with test_labels
# to find out how many are wrong.
matched = output==test_labels
correct_OP = np.count_nonzero(matched)
#Calculate the accuracy.
accuracy = (correct_OP*100.0)/(output.size)
# Display accuracy.



Well, I decided to workout myself on my question to solve the above problem. What I wanted is to implement a simple OCR using KNearest or SVM features in OpenCV. And below is what I did and how. (it is just for learning how to use KNearest for simple OCR purposes).

1) My first question was about file that comes with OpenCV samples. I wanted to know what is inside that file.

It contains a letter, along with 16 features of that letter.

And this SOF helped me to find it. These 16 features are explained in the paper Letter Recognition Using Holland-Style Adaptive Classifiers. (Although I didn't understand some of the features at the end)

2) Since I knew, without understanding all those features, it is difficult to do that method. I tried some other papers, but all were a little difficult for a beginner.

So I just decided to take all the pixel values as my features. (I was not worried about accuracy or performance, I just wanted it to work, at least with the least accuracy)

I took the below image for my training data:

enter image description here

(I know the amount of training data is less. But, since all letters are of the same font and size, I decided to try on this).

To prepare the data for training, I made a small code in OpenCV. It does the following things:

  1. It loads the image.
  2. Selects the digits (obviously by contour finding and applying constraints on area and height of letters to avoid false detections).
  3. Draws the bounding rectangle around one letter and wait for key press manually. This time we press the digit key ourselves corresponding to the letter in the box.
  4. Once the corresponding digit key is pressed, it resizes this box to 10x10 and saves all 100 pixel values in an array (here, samples) and corresponding manually entered digit in another array(here, responses).
  5. Then save both the arrays in separate .txt files.

At the end of the manual classification of digits, all the digits in the training data (train.png) are labeled manually by ourselves, image will look like below:

enter image description here

Below is the code I used for the above purpose (of course, not so clean):

import sys

import numpy as np
import cv2

im = cv2.imread('pitrain.png')
im3 = im.copy()

gray = cv2.cvtColor(im,cv2.COLOR_BGR2GRAY)
blur = cv2.GaussianBlur(gray,(5,5),0)
thresh = cv2.adaptiveThreshold(blur,255,1,1,11,2)

#################      Now finding Contours         ###################

contours,hierarchy = cv2.findContours(thresh,cv2.RETR_LIST,cv2.CHAIN_APPROX_SIMPLE)

samples =  np.empty((0,100))
responses = []
keys = [i for i in range(48,58)]

for cnt in contours:
    if cv2.contourArea(cnt)>50:
        [x,y,w,h] = cv2.boundingRect(cnt)
        if  h>28:
            roi = thresh[y:y+h,x:x+w]
            roismall = cv2.resize(roi,(10,10))
            key = cv2.waitKey(0)

            if key == 27:  # (escape to quit)
            elif key in keys:
                sample = roismall.reshape((1,100))
                samples = np.append(samples,sample,0)

responses = np.array(responses,np.float32)
responses = responses.reshape((responses.size,1))
print "training complete"


Now we enter in to training and testing part.

For the testing part, I used the below image, which has the same type of letters I used for the training phase.

enter image description here

For training we do as follows:

  1. Load the .txt files we already saved earlier
  2. create an instance of the classifier we are using (it is KNearest in this case)
  3. Then we use KNearest.train function to train the data

For testing purposes, we do as follows:

  1. We load the image used for testing
  2. process the image as earlier and extract each digit using contour methods
  3. Draw a bounding box for it, then resize it to 10x10, and store its pixel values in an array as done earlier.
  4. Then we use KNearest.find_nearest() function to find the nearest item to the one we gave. ( If lucky, it recognizes the correct digit.)

I included last two steps (training and testing) in single code below:

import cv2
import numpy as np

#######   training part    ############### 
samples = np.loadtxt('',np.float32)
responses = np.loadtxt('',np.float32)
responses = responses.reshape((responses.size,1))

model = cv2.KNearest()

############################# testing part  #########################

im = cv2.imread('pi.png')
out = np.zeros(im.shape,np.uint8)
gray = cv2.cvtColor(im,cv2.COLOR_BGR2GRAY)
thresh = cv2.adaptiveThreshold(gray,255,1,1,11,2)

contours,hierarchy = cv2.findContours(thresh,cv2.RETR_LIST,cv2.CHAIN_APPROX_SIMPLE)

for cnt in contours:
    if cv2.contourArea(cnt)>50:
        [x,y,w,h] = cv2.boundingRect(cnt)
        if  h>28:
            roi = thresh[y:y+h,x:x+w]
            roismall = cv2.resize(roi,(10,10))
            roismall = roismall.reshape((1,100))
            roismall = np.float32(roismall)
            retval, results, neigh_resp, dists = model.find_nearest(roismall, k = 1)
            string = str(int((results[0][0])))


And it worked, below is the result I got:

enter image description here

Here it worked with 100% accuracy. I assume this is because all the digits are of the same kind and the same size.

But anyway, this is a good start to go for beginners (I hope so).

Can't connect to Postgresql on port 5432

Remember to check firewall settings as well. after checking and double-checking my pg_hba.conf and postgres.conf files I finally found out that my firewall was overriding everything and therefore blocking connections

FontAwesome icons not showing. Why?

If you are using a newer version of Angular, just installing the package with npm/yarn is not enough. You also need to import the css file (with @import "~bootstrap-icons/font/bootstrap-icons.css";) in your styles.scss .

Using jquery to delete all elements with a given id

All your elements should have a unique IDs, so there should not be more than one element with #myid

An "id" is a unique identifier. Each time this attribute is used in a document it must have a different value. If you are using this attribute as a hook for style sheets it may be more appropriate to use classes (which group elements) than id (which are used to identify exactly one element).

Neverthless, try this:


How to get first two characters of a string in oracle query?

Try select substr(orderno, 1,2) from shipment;

Why can a function modify some arguments as perceived by the caller, but not others?

f doesn't actually alter the value of x (which is always the same reference to an instance of a list). Rather, it alters the contents of this list.

In both cases, a copy of a reference is passed to the function. Inside the function,

  • n gets assigned a new value. Only the reference inside the function is modified, not the one outside it.
  • x does not get assigned a new value: neither the reference inside nor outside the function are modified. Instead, x’s value is modified.

Since both the x inside the function and outside it refer to the same value, both see the modification. By contrast, the n inside the function and outside it refer to different values after n was reassigned inside the function.

React - clearing an input value after form submit

Since you input field is a controlled element, you cannot directly change the input field value without modifying the state.

Also in

onHandleSubmit(e) {
    const city =;
    this.mainInput.value = "";

this.mainInput doesn't refer the input since mainInput is an id, you need to specify a ref to the input

      ref={(ref) => this.mainInput= ref}
      placeholder="Get current weather..."

In you current state the best way is to clear the state to clear the input value

onHandleSubmit(e) {
    const city =;
    this.setState({city: ""});

However if you still for some reason want to keep the value in state even if the form is submitted, you would rather make the input uncontrolled

      placeholder="Get current weather..."

and update the value in state onChange and onSubmit clear the input using ref

 onHandleChange(e) {

  onHandleSubmit(e) {
    const city =;
    this.mainInput.value = "";

Having Said that, I don't see any point in keeping the state unchanged, so the first option should be the way to go.

How to change dataframe column names in pyspark?

If you want to rename a single column and keep the rest as it is:

from pyspark.sql.functions import col
new_df =*[col(s).alias(new_name) if s == column_to_change else s for s in old_df.columns])

What is the <leader> in a .vimrc file?

The "Leader key" is a way of extending the power of VIM's shortcuts by using sequences of keys to perform a command. The default leader key is backslash. Therefore, if you have a map of <Leader>Q, you can perform that action by typing \Q.

IDEA: javac: source release 1.7 requires target release 1.7

Most likely you have incorrect compiler options imported from Maven here:

compiler options

Also check project and module bytecode (target) version settings outlined on the screenshot.

Other places where the source language level is configured:

  • Project Structure | Project


  • Project Structure | Modules (check every module) | Sources


Maven default language level is 1.5 (5.0), you will see this version as the Module language level on the screenshot above.

This can be changed using maven-compiler-plugin configuration inside pom.xml:




IntelliJ IDEA will respect this setting after you Reimport the Maven project in the Maven Projects tool window:


Can I get div's background-image url?

I'm using this one

  function getBackgroundImageUrl($element) {
    if (!($element instanceof jQuery)) {
      $element = $($element);

    var imageUrl = $element.css('background-image');
    return imageUrl.replace(/(url\(|\)|'|")/gi, ''); // Strip everything but the url itself

How to concatenate multiple column values into a single column in Panda dataframe

The answer given by @allen is reasonably generic but can lack in performance for larger dataframes:

Reduce does a lot better:

from functools import reduce

import pandas as pd

# make data
df = pd.DataFrame(index=range(1_000_000))
df['1'] = 'CO'
df['2'] = 'BOB'
df['3'] = '01'
df['4'] = 'BILL'

def reduce_join(df, columns):
    assert len(columns) > 1
    slist = [df[x].astype(str) for x in columns]
    return reduce(lambda x, y: x + '_' + y, slist[1:], slist[0])

def apply_join(df, columns):
    assert len(columns) > 1
    return df[columns].apply(lambda row:'_'.join(row.values.astype(str)), axis=1)

# ensure outputs are equal
df1 = reduce_join(df, list('1234'))
df2 = apply_join(df, list('1234'))
assert df1.equals(df2)

# profile
%timeit df1 = reduce_join(df, list('1234'))  # 733 ms
%timeit df2 = apply_join(df, list('1234'))   # 8.84 s

"Mixed content blocked" when running an HTTP AJAX operation in an HTTPS page

I resolved this by adding following code to the HTML page, since we are using the third party API which is not controlled by us.

<meta http-equiv="Content-Security-Policy" content="upgrade-insecure-requests"> 

Hope this would help, and for a record as well.

Bootstrap table striped: How do I change the stripe background colour?

Easiest way for changing order of striped:

Add empty tr before your table tr tags.

return SQL table as JSON in python

Most simple way,

use json.dumps but if its datetime will require to parse datetime into json serializer.

here is mine,

import MySQLdb, re, json
from datetime import date, datetime

def json_serial(obj):
    """JSON serializer for objects not serializable by default json code"""

    if isinstance(obj, (datetime, date)):
        return obj.isoformat()
    raise TypeError ("Type %s not serializable" % type(obj))

conn = MySQLdb.connect(instance)
curr = conn.cursor()
curr.execute("SELECT * FROM `assets`")
data = curr.fetchall()
print json.dumps(data, default=json_serial)

it will return json dump

one more simple method without json dumps, here get header and use zip to map with each finally made it as json but this is not change datetime into json serializer...

data_json = []
header = [i[0] for i in curr.description]
data = curr.fetchall()
for i in data:
    data_json.append(dict(zip(header, i)))
print data_json

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)

matplotlib savefig() plots different from show()

I have fixed this in my matplotlib source, but it's not a pretty fix. However, if you, like me, are very particular about how the graph looks, it's worth it.

The issue seems to be in the rendering backends; they each get the correct values for linewidth, font size, etc., but that comes out slightly larger when rendered as a PDF or PNG than when rendered with show().

I added a few lines to the source for PNG generation, in the file matplotlib/backends/ You could make similar changes for each backend you use, or find a way to make a more clever change in a single location ;)

Added to my matplotlib/backends/ file:

    # The top of the file, added lines 42 - 44
42  # @warning: CHANGED FROM SOURCE to draw thinner lines
43  PATH_SCALAR = .8
44  FONT_SCALAR = .95

    # In the draw_markers method, added lines 90 - 91
89  def draw_markers(self, *kl, **kw):
90      # @warning: CHANGED FROM SOURCE to draw thinner lines
91      kl[0].set_linewidth(kl[0].get_linewidth()*PATH_SCALAR)
92      return self._renderer.draw_markers(*kl, **kw)

    # At the bottom of the draw_path method, added lines 131 - 132:
130 else:
131     # @warning: CHANGED FROM SOURCE to draw thinner lines
132     gc.set_linewidth(gc.get_linewidth()*PATH_SCALAR)
133     self._renderer.draw_path(gc, path, transform, rgbFace)

    # At the bottom of the _get_agg_font method, added line 242 and the *FONT_SCALAR
241     font.clear()
242     # @warning: CHANGED FROM SOURCE to draw thinner lines
243     size = prop.get_size_in_points()*FONT_SCALAR
244     font.set_size(size, self.dpi)

So that suits my needs for now, but, depending on what you're doing, you may want to implement similar changes in other methods. Or find a better way to do the same without so many line changes!

Update: After posting an issue to the matplotlib project at Github, I was able to track down the source of my problem: I had changed the figure.dpi setting in the matplotlibrc file. If that value is different than the default, my savefig() images come out different, even if I set the savefig dpi to be the same as the figure dpi. So, instead of changing the source as above, I just kept the figure.dpi setting as the default 80, and was able to generate images with savefig() that looked like images from show().

Leon, had you also changed that setting?

how to change any data type into a string in python

I see all answers recommend using str(object). It might fail if your object have more than ascii characters and you will see error like ordinal not in range(128). This was the case for me while I was converting list of string in language other than English

I resolved it by using unicode(object)

Getting HTTP headers with Node.js

Using the excellent request module:

var request = require('request');
  request("", {method: 'HEAD'}, function (err, res, body){

You can change the method to GET if you wish, but using HEAD will save you from getting the entire response body if you only wish to look at the headers.

Single Result from Database by using mySQLi

When just a single result is needed, then no loop should be used. Just fetch the row right away.

  • In case you need to fetch the entire row into associative array:

      $row = $result->fetch_assoc();
  • in case you need just a single value

      $row = $result->fetch_row();
      $value = $row[0] ?? false;

The last example will return the first column from the first returned row, or false if no row was returned. It can be also shortened to a single line,

$value = $result->fetch_row()[0] ?? false;

Below are complete examples for different use cases

Variables to be used in the query

When variables are to be used in the query, then a prepared statement must be used. For example, given we have a variable $id:

$query = "SELECT ssfullname, ssemail FROM userss WHERE ud=?";
$stmt = $conn->prepare($query);
$stmt->bind_param("s", $id);
$result = $stmt->get_result();
$row = $result->fetch_assoc();

// in case you need just a single value
$query = "SELECT count(*) FROM userss WHERE id=?";
$stmt = $conn->prepare($query);
$stmt->bind_param("s", $id);
$result = $stmt->get_result();
$value = $result->fetch_row()[0] ?? false;

The detailed explanation of the above process can be found in my article. As to why you must follow it is explained in this famous question

No variables in the query

In your case, where no variables to be used in the query, you can use the query() method:

$query = "SELECT ssfullname, ssemail FROM userss ORDER BY ssid";
$result = $conn->query($query);
// in case you need an array
$row = $result->fetch_assoc();
// OR in case you need just a single value
$value = $result->fetch_row()[0] ?? false;

By the way, although using raw API while learning is okay, consider using some database abstraction library or at least a helper function in the future:

// using a helper function
$sql = "SELECT email FROM users WHERE id=?";
$value = prepared_select($conn, $sql, [$id])->fetch_row[0] ?? false;

// using a database helper class
$email = $db->getCol("SELECT email FROM users WHERE id=?", [$id]);

As you can see, although a helper function can reduce the amount of code, a class' method could encapsulate all the repetitive code inside, making you to write only meaningful parts - the query, the input parameters and the desired result format (in the form of the method's name).

Git undo local branch delete

Thanks, this worked.

git branch new_branch_name sha1

git checkout new_branch_name

//can see my old checked in files in my old branch

CSS transition fade on hover

This will do the trick


  transition: opacity .2s ease-out;
  -moz-transition: opacity .2s ease-out;
  -webkit-transition: opacity .2s ease-out;
  -o-transition: opacity .2s ease-out;

Uncaught SyntaxError: Unexpected token with JSON.parse

Here's a function I made based on previous replies: it works on my machine but YMMV.

             * @description Converts a string response to an array of objects.
             * @param {string} string - The string you want to convert.
             * @returns {array} - an array of objects.
            function stringToJson(input) {
              var result = [];

              //replace leading and trailing [], if present
              input = input.replace(/^\[/,'');
              input = input.replace(/\]$/,'');

              //change the delimiter to 
              input = input.replace(/},{/g,'};;;{');

              // preserve newlines, etc - use valid JSON
            input = input.replace(/\\n/g, "\\n")  
            .replace(/\\'/g, "\\'")
            .replace(/\\"/g, '\\"')
            .replace(/\\&/g, "\\&")
            .replace(/\\r/g, "\\r")
            .replace(/\\t/g, "\\t")
            .replace(/\\b/g, "\\b")
            .replace(/\\f/g, "\\f");
            // remove non-printable and other non-valid JSON chars
            input = input.replace(/[\u0000-\u0019]+/g,""); 

              input = input.split(';;;');

              input.forEach(function(element) {
                // console.log(JSON.stringify(element));

              }, this);

              return result;

How does Django's Meta class work?

In Django, it acts as a configuration class and keeps the configuration data in one place!!

Node JS Error: ENOENT

To expand a bit on why the error happened: A forward slash at the beginning of a path means "start from the root of the filesystem, and look for the given path". No forward slash means "start from the current working directory, and look for the given path".

The path


thus translates to looking for the file test.jpg in the tmp folder at the root of the filesystem (e.g. c:\ on windows, / on *nix), instead of the webapp folder. Adding a period (.) in front of the path explicitly changes this to read "start from the current working directory", but is basically the same as leaving the forward slash out completely.

./tmp/test.jpg = tmp/test.jpg

Unable to install pyodbc on Linux

According to official Microsoft docs for Ubuntu 18.04 you should run next commands:

sudo su 
curl | apt-key add -
curl > /etc/apt/sources.list.d/mssql-release.list
apt-get update
ACCEPT_EULA=Y apt-get install msodbcsql17

If you are using python3.7, it is very important to run:

sudo apt-get install python3.7-dev

How to check the function's return value if true or false

false != 'false'

For good measures, put the result of validate into a variable to avoid double validation and use that in the IF statement. Like this:

var result = ValidateForm();
if(result == false) {

Android sample bluetooth code to send a simple string via bluetooth

I made the following code so that even beginners can understand. Just copy the code and read comments. Note that message to be send is declared as a global variable which you can change just before sending the message. General changes can be done in Handler function.

import android.annotation.SuppressLint;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.bluetooth.BluetoothServerSocket;
import android.bluetooth.BluetoothSocket;
import android.content.Intent;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Toast;

import java.util.ArrayList;
import java.util.Set;
import java.util.UUID;

public class multiplayerConnect extends AppCompatActivity {

public static final int REQUEST_ENABLE_BT=1;
ListView lv_paired_devices;
Set<BluetoothDevice> set_pairedDevices;
ArrayAdapter adapter_paired_devices;
BluetoothAdapter bluetoothAdapter;
public static final UUID MY_UUID = UUID.fromString("00001101-0000-1000-8000-00805F9B34FB");
public static final int MESSAGE_READ=0;
public static final int MESSAGE_WRITE=1;
public static final int CONNECTING=2;
public static final int CONNECTED=3;
public static final int NO_SOCKET_FOUND=4;

String bluetooth_message="00";

Handler mHandler=new Handler()
    public void handleMessage(Message msg_type) {

        switch (msg_type.what){
            case MESSAGE_READ:

                byte[] readbuf=(byte[])msg_type.obj;
                String string_recieved=new String(readbuf);

                //do some task based on recieved string

            case MESSAGE_WRITE:

                    ConnectedThread connectedThread=new ConnectedThread((BluetoothSocket)msg_type.obj);


            case CONNECTED:

            case CONNECTING:

            case NO_SOCKET_FOUND:
                Toast.makeText(getApplicationContext(),"No socket found",Toast.LENGTH_SHORT).show();

protected void onCreate(@Nullable Bundle savedInstanceState) {


public void start_accepting_connection()
    //call this on button click as suited by you

    AcceptThread acceptThread = new AcceptThread();
public void initialize_clicks()
    lv_paired_devices.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        public void onItemClick(AdapterView<?> parent, View view, int position, long id)
            Object[] objects = set_pairedDevices.toArray();
            BluetoothDevice device = (BluetoothDevice) objects[position];

            ConnectThread connectThread = new ConnectThread(device);

            Toast.makeText(getApplicationContext(),"device choosen "+device.getName(),Toast.LENGTH_SHORT).show();

public void initialize_layout()
    lv_paired_devices = (ListView)findViewById(;
    adapter_paired_devices = new ArrayAdapter(getApplicationContext(),R.layout.support_simple_spinner_dropdown_item);

public void initialize_bluetooth()
    bluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
    if (bluetoothAdapter == null) {
        // Device doesn't support Bluetooth
        Toast.makeText(getApplicationContext(),"Your Device doesn't support bluetooth. you can play as Single player",Toast.LENGTH_SHORT).show();

    //Add these permisions before
//        <uses-permission android:name="android.permission.BLUETOOTH" />
//        <uses-permission android:name="android.permission.BLUETOOTH_ADMIN" />
//        <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
//        <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/>

    if (!bluetoothAdapter.isEnabled()) {
        Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
        startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);

    else {
        set_pairedDevices = bluetoothAdapter.getBondedDevices();

        if (set_pairedDevices.size() > 0) {

            for (BluetoothDevice device : set_pairedDevices) {
                String deviceName = device.getName();
                String deviceHardwareAddress = device.getAddress(); // MAC address

                adapter_paired_devices.add(device.getName() + "\n" + device.getAddress());

public class AcceptThread extends Thread
    private final BluetoothServerSocket serverSocket;

    public AcceptThread() {
        BluetoothServerSocket tmp = null;
        try {
            // MY_UUID is the app's UUID string, also used by the client code
            tmp = bluetoothAdapter.listenUsingRfcommWithServiceRecord("NAME",MY_UUID);
        } catch (IOException e) { }
        serverSocket = tmp;

    public void run() {
        BluetoothSocket socket = null;
        // Keep listening until exception occurs or a socket is returned
        while (true) {
            try {
                socket = serverSocket.accept();
            } catch (IOException e) {

            // If a connection was accepted
            if (socket != null)
                // Do work to manage the connection (in a separate thread)

private class ConnectThread extends Thread {
    private final BluetoothSocket mmSocket;
    private final BluetoothDevice mmDevice;

    public ConnectThread(BluetoothDevice device) {
        // Use a temporary object that is later assigned to mmSocket,
        // because mmSocket is final
        BluetoothSocket tmp = null;
        mmDevice = device;

        // Get a BluetoothSocket to connect with the given BluetoothDevice
        try {
            // MY_UUID is the app's UUID string, also used by the server code
            tmp = device.createRfcommSocketToServiceRecord(MY_UUID);
        } catch (IOException e) { }
        mmSocket = tmp;

    public void run() {
        // Cancel discovery because it will slow down the connection

        try {
            // Connect the device through the socket. This will block
            // until it succeeds or throws an exception

        } catch (IOException connectException) {
            // Unable to connect; close the socket and get out
            try {
            } catch (IOException closeException) { }

        // Do work to manage the connection (in a separate thread)
//            bluetooth_message = "Initial message"
//            mHandler.obtainMessage(MESSAGE_WRITE,mmSocket).sendToTarget();

    /** Will cancel an in-progress connection, and close the socket */
    public void cancel() {
        try {
        } catch (IOException e) { }
private class ConnectedThread extends Thread {

    private final BluetoothSocket mmSocket;
    private final InputStream mmInStream;
    private final OutputStream mmOutStream;

    public ConnectedThread(BluetoothSocket socket) {
        mmSocket = socket;
        InputStream tmpIn = null;
        OutputStream tmpOut = null;

        // Get the input and output streams, using temp objects because
        // member streams are final
        try {
            tmpIn = socket.getInputStream();
            tmpOut = socket.getOutputStream();
        } catch (IOException e) { }

        mmInStream = tmpIn;
        mmOutStream = tmpOut;

    public void run() {
        byte[] buffer = new byte[2];  // buffer store for the stream
        int bytes; // bytes returned from read()

        // Keep listening to the InputStream until an exception occurs
        while (true) {
            try {
                // Read from the InputStream
                bytes =;
                // Send the obtained bytes to the UI activity
                mHandler.obtainMessage(MESSAGE_READ, bytes, -1, buffer).sendToTarget();

            } catch (IOException e) {

    /* Call this from the main activity to send data to the remote device */
    public void write(byte[] bytes) {
        try {
        } catch (IOException e) { }

    /* Call this from the main activity to shutdown the connection */
    public void cancel() {
        try {
        } catch (IOException e) { }


<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android=""

        android:text="Challenge player"/>


        android:text="Make sure Device is paired"/>


Import existing Gradle Git project into Eclipse

Open eclipse and right click in the package explorer ? import Select gradle Browse to the location where you checked out Click “Build Model” Select all the projects and hit finish

change image opacity using javascript

You could use Jquery indeed or plain good old javascript:

var opacityPercent=30;
document.getElementById("id").style.cssText="opacity:0."+opacityPercent+"; filter:progid:DXImageTransform.Microsoft.Alpha(style=0,opacity="+opacityPercent+");";

You put this in a function that you call on a setTimeout until the desired opacity is reached

Adjust width and height of iframe to fit with content in it

For angularjs directive attribute:

G.directive ( 'previewIframe', function () {
return {
    restrict : 'A',
    replace : true,
    scope : true,
    link : function ( scope, elem, attrs ) {
        elem.on ( 'load', function ( e ) {
            var currentH = this.contentWindow.document.body.scrollHeight;
   = eval( currentH ) + ( (25 / 100)* eval( currentH ) ) + 'px';
        } );
} );

Notice the percentage, i inserted it so that you can counter scaling usually done for iframe, text, ads etc, simply put 0 if no scaling is implementation

Dynamically adding elements to ArrayList in Groovy

The Groovy way to do this is

def list = []
list << new MyType(...)

which creates a list and uses the overloaded leftShift operator to append an item

See the Groovy docs on Lists for lots of examples.

How to include a font .ttf using CSS?

I know this is an old post but this solved my problem.

  font-family: "Font Name";_x000D_
  src: url("../fonts/font-name.ttf") format("truetype");_x000D_

notice src:url("../fonts/font-name.ttf"); we use two periods to go back to the root directory and then into the fonts folder or wherever your file is located.

hope this helps someone down the line:) happy coding

REST API - Use the "Accept: application/json" HTTP Header

Here's a handy site to test out your headers. You can see your browser headers and also use cURL to reflect back whatever headers you send.

For example, you can validate the content negotiation like this.

This Accept header prefers plain text so returns in that format:-

$ curl -H "Accept: application/json;q=0.9,text/plain"

Whereas this one prefers JSON and so returns in that format:-

$ curl -H "Accept: application/json,text/*;q=0.99"
   "Accept": "application/json,text/*;q=0.99"

Read line by line in bash script

If you want to use each of the lines of the file as command-line params for your application you can use the xargs command.

xargs -a <params_file> <command>

A params file with:


and the file

import sys
print sys.argv

The execution of

xargs -a params ./

gives the result:

['./', 'a', 'b', 'c', 'd']

ORA-01036: illegal variable name/number when running query through C#

You defined one oracleCommand but used it in 'for'. it means you are adding parameter with the same name to one OracleCommand. you should use cmd.Parameters.clear() to refresh your parameters.

for(int i=0;i<usersList.Count;i++)
            if (!(selectedUsersArray[i].Equals("")) && !passwordArray[i].Equals(""))
                cmd.Parameters.clear();//Add this line
                OracleParameter userName = new OracleParameter();
                userName.ParameterName = "user";
                userName.Value = selectedUsersArray[i];

                OracleParameter passwd = new OracleParameter();
                passwd.ParameterName = "password";
                passwd.Value = passwordArray[i];




Troubleshooting "Illegal mix of collations" error in mysql

Adding my 2c to the discussion for future googlers.

I was investigating a similar issue where I got the following error when using custom functions that recieved a varchar parameter:

Illegal mix of collations (utf8_unicode_ci,IMPLICIT) and 
(utf8_general_ci,IMPLICIT) for operation '='

Using the following query:

mysql> show variables like "collation_database";
    | Variable_name      | Value           |
    | collation_database | utf8_general_ci |

I was able to tell that the DB was using utf8_general_ci, while the tables were defined using utf8_unicode_ci:

mysql> show table status;
    | Name         | Collation       |
    | my_view      | NULL            |
    | my_table     | utf8_unicode_ci |

Notice that the views have NULL collation. It appears that views and functions have collation definitions even though this query shows null for one view. The collation used is the DB collation that was defined when the view/function were created.

The sad solution was to both change the db collation and recreate the views/functions to force them to use the current collation.

  • Changing the db's collation:

    ALTER DATABASE mydb DEFAULT COLLATE utf8_unicode_ci;
  • Changing the table collation:


I hope this will help someone.

How can I insert a line break into a <Text> component in React Native?

do this:


 { "Hi~ \n this is a test message." }


Turn off constraints temporarily (MS SQL)

Disabling and Enabling All Foreign Keys

CREATE PROCEDURE pr_Disable_Triggers_v2
    @disable BIT = 1
    DECLARE @sql VARCHAR(500)
        ,   @tableName VARCHAR(128)
        ,   @tableSchema VARCHAR(128)

    -- List of all tables
    DECLARE triggerCursor CURSOR FOR
        SELECT  t.TABLE_NAME AS TableName
            ,   t.TABLE_SCHEMA AS TableSchema

    OPEN    triggerCursor
    FETCH NEXT FROM triggerCursor INTO @tableName, @tableSchema
    WHILE ( @@FETCH_STATUS = 0 )

        SET @sql = 'ALTER TABLE ' + @tableSchema + '.[' + @tableName + '] '
        IF @disable = 1
            SET @sql = @sql + ' DISABLE TRIGGER ALL'
            SET @sql = @sql + ' ENABLE TRIGGER ALL'

        PRINT 'Executing Statement - ' + @sql
        EXECUTE ( @sql )

        FETCH NEXT FROM triggerCursor INTO @tableName, @tableSchema


    CLOSE triggerCursor
    DEALLOCATE triggerCursor

First, the foreignKeyCursor cursor is declared as the SELECT statement that gathers the list of foreign keys and their table names. Next, the cursor is opened and the initial FETCH statement is executed. This FETCH statement will read the first row's data into the local variables @foreignKeyName and @tableName. When looping through a cursor, you can check the @@FETCH_STATUS for a value of 0, which indicates that the fetch was successful. This means the loop will continue to move forward so it can get each successive foreign key from the rowset. @@FETCH_STATUS is available to all cursors on the connection. So if you are looping through multiple cursors, it is important to check the value of @@FETCH_STATUS in the statement immediately following the FETCH statement. @@FETCH_STATUS will reflect the status for the most recent FETCH operation on the connection. Valid values for @@FETCH_STATUS are:

0 = FETCH was successful
-1 = FETCH was unsuccessful
-2 = the row that was fetched is missing

Inside the loop, the code builds the ALTER TABLE command differently depending on whether the intention is to disable or enable the foreign key constraint (using the CHECK or NOCHECK keyword). The statement is then printed as a message so its progress can be observed and then the statement is executed. Finally, when all rows have been iterated through, the stored procedure closes and deallocates the cursor.

see Disabling Constraints and Triggers from MSDN Magazine

AngularJS - $ send data as json

Consider explicitly setting the header in the $ (I put application/json, as I am not sure which of the two versions in your example is the working one, but you can use application/x-www-form-urlencoded if it's the other one):

$"/customer/data/autocomplete", {term: searchString}, {headers: {'Content-Type': 'application/json'} })
        .then(function (response) {
            return response;

Cannot lower case button text in android studio

add android:textAllCaps="false" in xml button It's true with this issue.

jQuery Datepicker with text input that doesn't allow user input

You have two options to get this done. (As far as i know)

  1. Option A: Make your text field read only. It can be done as follows.

  2. Option B: Change the curser onfocus. Set ti to blur. it can be done by setting up the attribute onfocus="this.blur()" to your date picker text field.

Ex: <input type="text" name="currentDate" id="currentDate" onfocus="this.blur()" readonly/>

Returning multiple objects in an R function

One way to handle this is to put the information as an attribute on the primary one. I must stress, I really think this is the appropriate thing to do only when the two pieces of information are related such that one has information about the other.

For example, I sometimes stash the name of "crucial variables" or variables that have been significantly modified by storing a list of variable names as an attribute on the data frame:

attr(my.DF, 'Modified.Variables') <- DVs.For.Analysis$Names.of.Modified.Vars

This allows me to store a list of variable names with the data frame itself.

How to switch between python 2.7 to python 3 from command line?

There is an easier way than all of the above; You can use the PY_PYTHON environment variable. From inside the cmd.exe shell;

For the latest version of Python 2


For the latest version of Python 3


If you want it to be permanent, set it in the control panel. Or use setx instead of set in the cmd.exe shell.

VBA EXCEL Multiple Nested FOR Loops that Set two variable for expression

I can't get to your google docs file at the moment but there are some issues with your code that I will try to address while answering

Sub stituterangersNEW()
Dim t As Range
Dim x As Range
Dim dify As Boolean
Dim difx As Boolean
Dim time2 As Date
Dim time1 As Date

    'You said time1 doesn't change, so I left it in a singe cell.
    'If that is not correct, you will have to play with this some more.
    time1 = Range("A6").Value

    'Looping through each of our output cells.
    For Each t In Range("B7:E9") 'Change these to match your real ranges.

        'Looping through each departure date/time.
        '(Only one row in your example. This can be adjusted if needed.)
        For Each x In Range("B2:E2") 'Change these to match your real ranges.
            'Check to see if our dep time corresponds to
            'the matching column in our output
            If t.Column = x.Column Then
                'If it does, then check to see what our time value is
                If x > 0 Then
                    time2 = x.Value
                    'Apply the change to the output cell.
                    t.Value = time1 - time2
                    'Exit out of this loop and move to the next output cell.
                    Exit For
                End If
            End If
            'If the columns don't match, or the x value is not a time
            'then we'll move to the next dep time (x)
        Next x
    Next t

End Sub


I changed you worksheet to play with (see above for the new Sub). This probably does not suite your needs directly, but hopefully it will demonstrate the conept behind what I think you want to do. Please keep in mind that this code does not follow all the coding best preactices I would recommend (e.g. validating the time is actually a TIME and not some random other data type).

     A                      B                   C                   D                  E
1    LOAD_NUMBER            1                   2                   3                  4
2    DEPARTURE_TIME_DATE    11/12/2011 19:30    11/12/2011 19:30    11/12/2011 19:30    11/12/2011 20:00                
4    Dry_Refrig 7585.1  0   10099.8 16700
6    1/4/2012 19:30

Using the sub I got this output:

    A           B             C             D             E
7   Friday      1272:00:00    1272:00:00    1272:00:00    1271:30:00
8   Saturday    1272:00:00    1272:00:00    1272:00:00    1271:30:00
9   Thursday    1272:00:00    1272:00:00    1272:00:00    1271:30:00

How can I prevent the textarea from stretching beyond his parent DIV element? (google-chrome issue only)

Textarea resize control is available via the CSS3 resize property:

textarea { resize: both; } /* none|horizontal|vertical|both */
textarea.resize-vertical{ resize: vertical; }
textarea.resize-none { resize: none; }

Allowable values self-explanatory: none (disables textarea resizing), both, vertical and horizontal.

Notice that in Chrome, Firefox and Safari the default is both.

If you want to constrain the width and height of the textarea element, that's not a problem: these browsers also respect max-height, max-width, min-height, and min-width CSS properties to provide resizing within certain proportions.

Code example:

#textarea-wrapper {_x000D_
  padding: 10px;_x000D_
  background-color: #f4f4f4;_x000D_
  width: 300px;_x000D_
#textarea-wrapper textarea {_x000D_
  width: 290px;_x000D_
#textarea-wrapper textarea.vertical { _x000D_
  resize: vertical;_x000D_
<div id="textarea-wrapper">_x000D_
  <label for="resize-default">Textarea (default):</label>_x000D_
  <textarea name="resize-default" id="resize-default"></textarea>_x000D_
  <label for="resize-vertical">Textarea (vertical):</label>_x000D_
  <textarea name="resize-vertical" id="resize-vertical" class="vertical">Notice this allows only vertical resize!</textarea>_x000D_

MySQL server has gone away - in exactly 60 seconds

This is something I do, (but usually with the MySQLi class).

$link = mysql_connect("$MYSQL_Host","$MYSQL_User","$MYSQL_Pass");
mysql_select_db($MYSQL_db, $link);


// Reconnect if needed

if( !mysql_ping($link) ) $link = mysql_connect("$MYSQL_Host","$MYSQL_User","$MYSQL_Pass", true);


How to get First and Last record from a sql query?

[Caveat: Might not be the most efficient way to do it]:

(SELECT <some columns>
FROM mytable
<maybe some joins here>
WHERE <various conditions>


(SELECT <some columns>
FROM mytable
<maybe some joins here>
WHERE <various conditions>
ORDER BY date ASC    

How to insert newline in string literal?

string myText =
    @"<div class=""firstLine""></div>
      <div class=""secondLine""></div>
      <div class=""thirdLine""></div>";

that's not it:

string myText =
@"<div class=\"firstLine\"></div>
  <div class=\"secondLine\"></div>
  <div class=\"thirdLine\"></div>";

What's the difference between xsd:include and xsd:import?

Use xsd:include brings all declarations and definitions of an external schema document into the current schema.

Use xsd:import to bring in an XSD from a different namespace and used to build a new schema by extending existing schema documents..

How to make promises work in IE11

You could try using a Polyfill. The following Polyfill was published in 2019 and did the trick for me. It assigns the Promise function to the window object.

used like: window.Promise

If you want more information on Polyfills check out the following MDN web doc

How to get the path of current worksheet in VBA?

Use Application.ActiveWorkbook.Path for just the path itself (without the workbook name) or Application.ActiveWorkbook.FullName for the path with the workbook name.

Remove querystring from URL

var path = "path/to/myfile.png?foo=bar#hash";

    path.replace(/(\?.*)|(#.*)/g, "")

installing cPickle with python 3.5

cPickle comes with the standard library… in python 2.x. You are on python 3.x, so if you want cPickle, you can do this:

>>> import _pickle as cPickle

However, in 3.x, it's easier just to use pickle.

No need to install anything. If something requires cPickle in python 3.x, then that's probably a bug.

log4j:WARN No appenders could be found for logger in web.xml

In my case the solution was easy. You don't need to declare anything in your web.xml.

Because your project is a web application, the config file should be on WEB-INF/classes after deployment. I advise you to create a Java resource folder (src/main/resources) to do that (best pratice). Another approach is to put the config file in your src/main/java.

Beware with the configuration file name. If you are using XML, the file name is log4j.xml, otherwise

Get text of the selected option with jQuery

$(document).ready(function() {
    $('select#select_2').change(function() {
        var selectedText = $(this).find('option:selected').text();


how to find seconds since 1970 in java

The answer you want, "1317427200", is achieved if your reference months are January and October. If so, the dates you are looking for are 1970-JAN-01 and 2011-OCT-01, correct?

Then the problem are these numbers you are using for your months.

See, if you check the Calendar API documentation or even the constants provided in there ("Calendar.JANUARY", "Calendar.FEBRUARY" and so on), you'll discover that months start at 0 (being January).

So checking your code, you are passing february and november, which would result in "1317510000".

Best regards.

Avoid "current URL string parser is deprecated" warning by setting useNewUrlParser to true

Check your mongo version:

mongo --version

If you are using version >= 3.1.0, change your mongo connection file to ->

MongoClient.connect("mongodb://localhost:27017/YourDB", { useNewUrlParser: true })

or your mongoose connection file to ->

mongoose.connect("mongodb://localhost:27017/YourDB", { useNewUrlParser: true });

Ideally, it's a version 4 feature, but v3.1.0 and above are supporting it too. Check out MongoDB GitHub for details.

Request UAC elevation from within a Python script?

It seems there's no way to elevate the application privileges for a while for you to perform a particular task. Windows needs to know at the start of the program whether the application requires certain privileges, and will ask the user to confirm when the application performs any tasks that need those privileges. There are two ways to do this:

  1. Write a manifest file that tells Windows the application might require some privileges
  2. Run the application with elevated privileges from inside another program

This two articles explain in much more detail how this works.

What I'd do, if you don't want to write a nasty ctypes wrapper for the CreateElevatedProcess API, is use the ShellExecuteEx trick explained in the Code Project article (Pywin32 comes with a wrapper for ShellExecute). How? Something like this:

When your program starts, it checks if it has Administrator privileges, if it doesn't it runs itself using the ShellExecute trick and exits immediately, if it does, it performs the task at hand.

As you describe your program as a "script", I suppose that's enough for your needs.


jQuery detect if textarea is empty

$.each(["input[type=text][value=]", "textarea[value=]"], function (index, element) {
              //only empty input and textarea will come here

How does OkHttp get Json string?

I am also faced the same issue

use this code:

// notice string() call
String resStr = response.body().string();    
JSONObject json = new JSONObject(resStr);

it definitely works

Does static constexpr variable inside a function make sense?

The short answer is that not only is static useful, it is pretty well always going to be desired.

First, note that static and constexpr are completely independent of each other. static defines the object's lifetime during execution; constexpr specifies that the object should be available during compilation. Compilation and execution are disjoint and discontiguous, both in time and space. So once the program is compiled, constexpr is no longer relevant.

Every variable declared constexpr is implicitly const but const and static are almost orthogonal (except for the interaction with static const integers.)

The C++ object model (§1.9) requires that all objects other than bit-fields occupy at least one byte of memory and have addresses; furthermore all such objects observable in a program at a given moment must have distinct addresses (paragraph 6). This does not quite require the compiler to create a new array on the stack for every invocation of a function with a local non-static const array, because the compiler could take refuge in the as-if principle provided it can prove that no other such object can be observed.

That's not going to be easy to prove, unfortunately, unless the function is trivial (for example, it does not call any other function whose body is not visible within the translation unit) because arrays, more or less by definition, are addresses. So in most cases, the non-static const(expr) array will have to be recreated on the stack at every invocation, which defeats the point of being able to compute it at compile time.

On the other hand, a local static const object is shared by all observers, and furthermore may be initialized even if the function it is defined in is never called. So none of the above applies, and a compiler is free not only to generate only a single instance of it; it is free to generate a single instance of it in read-only storage.

So you should definitely use static constexpr in your example.

However, there is one case where you wouldn't want to use static constexpr. Unless a constexpr declared object is either ODR-used or declared static, the compiler is free to not include it at all. That's pretty useful, because it allows the use of compile-time temporary constexpr arrays without polluting the compiled program with unnecessary bytes. In that case, you would clearly not want to use static, since static is likely to force the object to exist at runtime.

How can I find the number of elements in an array?

If you have your array in scope you can use sizeof to determine its size in bytes and use the division to calculate the number of elements:

#define NUM_OF_ELEMS 10
int arr[NUM_OF_ELEMS];
size_t NumberOfElements = sizeof(arr)/sizeof(arr[0]);

If you receive an array as a function argument or allocate an array in heap you can not determine its size using the sizeof. You'll have to store/pass the size information somehow to be able to use it:

void DoSomethingWithArray(int* arr, int NumOfElems)
    for(int i = 0; i < NumOfElems; ++i) {
        arr[i] = /*...*/

Linq with group by having count

Like this:

from c in db.Company
group c by c.Name into grp
where grp.Count() > 1
select grp.Key

Or, using the method syntax:

    .GroupBy(c => c.Name)
    .Where(grp => grp.Count() > 1)
    .Select(grp => grp.Key);

Tab separated values in awk

You can set the Field Separator:

... | awk 'BEGIN {FS="\t"}; {print $1}'

Excellent read:

How can I analyze a heap dump in IntelliJ? (memory leak)

I would like to update the answers above to 2018 and say to use both VisualVM and Eclipse MAT.

How to use:

VisualVM is used for live monitoring and dump heap. You can also analyze the heap dumps there with great power, however MAT have more capabilities (such as automatic analysis to find leaks) and therefore, I read the VisualVM dump output (.hprof file) into MAT.

Get VisualVM:

Download VisualVM here:

You also need to download the plugin for Intellij: enter image description here

Then you'll see in intellij another 2 new orange icons: enter image description here

Once you run your app with an orange one, in VisualVM you'll see your process on the left, and data on the right. Sit some time and learn this tool, it is very powerful: enter image description here

Get Eclipse's Memory Analysis Tool (MAT) as a standalone:

Download here:

And this is how it looks: enter image description here enter image description here

Hope it helps!

Using an authorization header with Fetch in React Native

completed = (id) => {
    var details = {
        'id': id,


    var formBody = [];
    for (var property in details) {
        var encodedKey = encodeURIComponent(property);
        var encodedValue = encodeURIComponent(details[property]);
        formBody.push(encodedKey + "=" + encodedValue);
    formBody = formBody.join("&");

    fetch(markcompleted, {
        method: 'POST',
        headers: {
            'Accept': 'application/json',
            'Content-Type': 'application/x-www-form-urlencoded'
        body: formBody
        .then((response) => response.json())
        .then((responseJson) => {
            console.log(responseJson, 'res JSON');
            if (responseJson.status == "success") {
                alert("your todolist is completed!!");
        .catch((error) => {

Configuring angularjs with eclipse IDE

Since these previous answers above, there is now a release of an Eclipse Plugin to assist with development using AngularJS: (take a look around the other Wiki pages for information on features)

The release at the time of the answer is 0.1.0.

Please also checkout JSDT ( and also Eclipse VJET ( The VJET project appears to be an attempt to provide better feature sets to the editor without being encumbered by the JSDT project (open source politics at play I guess).

Running Facebook application on localhost

In my case the issue revealed to be chrome blocking the CORS request from localhost:4200 to facebook api website. Running Chrome with this setting: "YOUR_PATH_TO_CHROME\Google\Chrome\Application\chrome.exe" --disable-web-security --user-data-dir="c:/chrome worked like a charm while developing. Even with no localhost added to facebook app's settings.

Convert JSON array to Python list

Tested on Ideone.

import json
array = '{"fruits": ["apple", "banana", "orange"]}'
data  = json.loads(array)
fruits_list = data['fruits']
print fruits_list

Activate tabpage of TabControl

You can use the method SelectTab.

There are 3 versions:

public void SelectTab(int index);
public void SelectTab(string tabPageName);
public void SelectTab(TabPage tabPage);

How to Use Multiple Columns in Partition By And Ensure No Duplicate Row is Returned

Try this, It worked for me

                ROW_NUMBER() OVER(PARTITION BY [Code],[Name],[CategoryCode] ORDER BY ID DESC) rownumber
            FROM MasterTable
          ) a
        WHERE rownumber = 1 

Xcode Product -> Archive disabled

You've changed your scheme destination to a simulator instead of Generic iOS Device.

That's why it is greyed out.

Change from a simulator to Generic iOS Device

Invalid column name sql error

first create database name "School" than create table "students" with following columns 1. id 2. name 3. address

now open visual studio and create connection:

namespace school
    public partial class Form1 : Form
        SqlConnection scon;

        public Form1()


            scon = new SqlConnection("Data Source = ABC-PC; trusted_connection = yes; Database = school; connection timeout = 30");

//create command

SqlCommand scom = new SqlCommand("insert into students (id,name,address) values(@id,@name,@address)", scon);

//pass parameters

scom.Parameters.Add("id", SqlDbType.Int);
scom.Parameters["id"].Value = textBox1.Text;

           scom.Parameters.Add("name", SqlDbType.VarChar);
            scom.Parameters["name"].Value = this.textBox2.Text;

            scom.Parameters.Add("address", SqlDbType.VarChar);
            scom.Parameters["address"].Value = this.textBox6.Text;



also check solution here:

How can I split a string with a string delimiter?

There is a version of string.Split that takes an array of strings and a StringSplitOptions parameter:

What does FETCH_HEAD in Git mean?

I have just discovered and used FETCH_HEAD. I wanted a local copy of some software from a server and I did

git fetch gitserver release_1

gitserver is the name of my machine that stores git repositories. release_1 is a tag for a version of the software. To my surprise, release_1 was then nowhere to be found on my local machine. I had to type

 git tag release_1 FETCH_HEAD 

to complete the copy of the tagged chain of commits (release_1) from the remote repository to the local one. Fetch had found the remote tag, copied the commit to my local machine, had not created a local tag, but had set FETCH_HEAD to the value of the commit, so that I could find and use it. I then used FETCH_HEAD to create a local tag which matched the tag on the remote. That is a practical illustration of what FETCH_HEAD is and how it can be used, and might be useful to someone else wondering why git fetch doesn't do what you would naively expect.

In my opinion it is best avoided for that purpose and a better way to achieve what I was trying to do is

git fetch gitserver release_1:release_1

i.e. to fetch release_1 and call it release_1 locally. (It is source:dest, see; just in case you'd like to give it a different name!)

You might want to use FETCH_HEAD at times though:-

git fetch gitserver bugfix1234
git cherry-pick FETCH_HEAD

might be a nice way of using bug fix number 1234 from your Git server, and leaving Git's garbage collection to dispose of the copy from the server once the fix has been cherry-picked onto your current branch. (I am assuming that there is a nice clean tagged commit containing the whole of the bug fix on the server!)

How to handle the modal closing event in Twitter Bootstrap?

If you want specifically do something when click on close button exactly like you described:

<a href="#" class="btn close_link" data-dismiss="modal">Close</a>

you need to attach an event using css selector:

$(document).on('click', '[data-dismiss="modal"]', function(){what you want to do})

But if you want to do something when modal close, you can use the already wrote tips

Find common substring between two strings


import itertools as it
''.join(el[0] for el in it.takewhile(lambda t: t[0] == t[1], zip(string1, string2)))

It does the comparison from the beginning of both strings.

Trying to start a service on boot on Android

The other answers look good, but I thought I'd wrap everything up into one complete answer.

You need the following in your AndroidManifest.xml file:

  1. In your <manifest> element:

    <uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED" />
  2. In your <application> element (be sure to use a fully-qualified [or relative] class name for your BroadcastReceiver):

    <receiver android:name="com.example.MyBroadcastReceiver">  
            <action android:name="android.intent.action.BOOT_COMPLETED" />  

    (you don't need the android:enabled, exported, etc., attributes: the Android defaults are correct)


    package com.example;
    public class MyBroadcastReceiver extends BroadcastReceiver {
        public void onReceive(Context context, Intent intent) {
            Intent startServiceIntent = new Intent(context, MyService.class);

From the original question:

  • it's not clear if the <receiver> element was in the <application> element
  • it's not clear if the correct fully-qualified (or relative) class name for the BroadcastReceiver was specified
  • there was a typo in the <intent-filter>

How to open existing project in Eclipse

Assume that the application folder is in your pen drive.

open eclipse, go to import,select Android,In Android select "existing android code into workspace"

next and finish.

Ramanand Bhat

Run a command shell in jenkins

For Windows slave, please use Execute Windows batch command.
For Unix-like slave like linux or Mac, Execute shell is the option.

Execute Windows Command shell

Import data into Google Colaboratory


from google.colab import files


List directory


How to insert date values into table

Since dob is DATE data type, you need to convert the literal to DATE using TO_DATE and the proper format model. The syntax is:

TO_DATE('<date_literal>', '<format_model>')

For example,


Table created.

SQL> INSERT INTO t(dob) VALUES(TO_DATE('17/12/2015', 'DD/MM/YYYY'));

1 row created.


Commit complete.



A DATE data type contains both date and time elements. If you are not concerned about the time portion, then you could also use the ANSI Date literal which uses a fixed format 'YYYY-MM-DD' and is NLS independent.

For example,

SQL> INSERT INTO t(dob) VALUES(DATE '2015-12-17');

1 row created.

In MySQL, how to copy the content of one table to another table within the same database?

If you want to create and copy the content in a single shot, just use the SELECT:

CREATE TABLE new_tbl SELECT * FROM orig_tbl;

How to get an enum value from a string value in Java?

You should also be careful with your case. Let me explain: doing Blah.valueOf("A") works, but Blah.valueOf("a") will not work. Then again Blah.valueOf("a".toUpperCase(Locale.ENGLISH)) would work.

Changed toUpperCase to toUpperCase(Locale.ENGLISH) based on tc. comment and the java docs

edit2 On android you should use Locale.US, as sulai points out.

How to strip all whitespace from string

As mentioned by Roger Pate following code worked for me:

s = " \t foo \n bar "

I am using Jupyter Notebook to run following code:

while i < len(new_list): 
   temp=''                            # new_list[i]=temp=' Plain   Utthapam  '
   #temp=new_list[i].strip()          #if we want o/p as: 'Plain Utthapam'
   temp="".join(new_list[i].split())  #o/p: 'PlainUtthapam' 
   temp=temp.upper()                  #o/p:'PLAINUTTHAPAM' 

Compile error: package javax.servlet does not exist

This is what I found. Adding /usr/local/apache-tomcat-7.0.64/lib/servlet-api.jar in my environment variable as CLASSPATH. OS is iOS.

if using bash: ~/.bash_profile $CLASSPATH=/usr/local/apache-tomcat-7.0.64/lib/servlet-api.jar

if using zsh: ~/.zshrc export CLASSPATH="usr/local/apache-tomcat-7.0.64/lib/servlet-api.jar"

Force it work right now, run source .bash_profile (or .zshrc) or one can restart computer and it works for the current user.

How do I query between two dates using MySQL?

Your query should have date as

select * from table between `lowerdate` and `upperdate`


SELECT * FROM `objects` 
WHERE  (date_field BETWEEN '2010-01-30 14:15:55' AND '2010-09-29 10:15:55')

How do I collapse a table row in Bootstrap?

You can do this without any JavaScript involved

(Using accepted answer)


<table class="table table-bordered table-striped">
        <td><button class="btn" data-target="#collapseme" data-toggle="collapse" type="button">Click to expand</button></td>
        <td class="nopadding">
            <div class="collapse" id="collapseme">
                <div class="content">
                    Show me collapsed


.nopadding {
    padding: 0 !important;

.content {
    padding: 20px;

HTML5 input type range show range value

For people don't care about jquery use, here is a short way without using any id

<label> userAvatar :
  <input type="range" name="userAvatar" min="1" max="100" value="1"
         onchange="$('~ output', this).val(value)" 
         oninput="$('~ output', this).val(value)">

How to execute a JavaScript function when I have its name as a string

You can call javascript function within the eval("functionname as string") either. Like below: (eval is pure javascript function)

function testfunc(){
    return "hello world";

$( document ).ready(function() {


Working example:

How to override a JavaScript function

var origParseFloat = parseFloat;
parseFloat = function(str) {
     alert("And I'm in your floats!");
     return origParseFloat(str);

Log4net rolling daily filename with date in the file name

<appender name="RollingLogFileAppender" type="log4net.Appender.RollingFileAppender">
  <lockingModel type="log4net.Appender.FileAppender+MinimalLock"/>
  <file value="logs\" />
  <datePattern value="dd.MM.yyyy'.log'" />
  <staticLogFileName value="false" />
  <appendToFile value="true" />
  <rollingStyle value="Composite" />
  <maxSizeRollBackups value="10" />
  <maximumFileSize value="5MB" />
  <layout type="log4net.Layout.PatternLayout">
    <conversionPattern value="%date [%thread] %-5level %logger [%property{NDC}] - %message%newline" />

How to show Page Loading div until the page has finished loading?

Here's the jQuery I ended up using, which monitors all ajax start/stop, so you don't need to add it to each ajax call:


CSS for the loading container & content (mostly from mehyaa's answer), as well as a hide class:

#loading {
   width: 100%;
   height: 100%;
   top: 0px;
   left: 0px;
   position: fixed;
   display: block;
   opacity: 0.7;
   background-color: #fff;
   z-index: 99;
   text-align: center;

#loading-content {
  position: absolute;
  top: 50%;
  left: 50%;
  text-align: center;
  z-index: 100;

  display: none;


<div id="loading" class="hide">
  <div id="loading-content">

CustomErrors mode="Off"

You can also try bringing up the website in a browser on the server machine. I don't do a lot of ASP.NET development, but I remember the custom errors thing has a setting for only displaying full error text on the server, as a security measure.

Substitute multiple whitespace with single whitespace in Python

A regular expression can be used to offer more control over the whitespace characters that are combined.

To match unicode whitespace:

import re

_RE_COMBINE_WHITESPACE = re.compile(r"\s+")

my_str = _RE_COMBINE_WHITESPACE.sub(" ", my_str).strip()

To match ASCII whitespace only:

import re

_RE_COMBINE_WHITESPACE = re.compile(r"(?a:\s+)")
_RE_STRIP_WHITESPACE = re.compile(r"(?a:^\s+|\s+$)")

my_str = _RE_COMBINE_WHITESPACE.sub(" ", my_str)
my_str = _RE_STRIP_WHITESPACE.sub("", my_str)

Matching only ASCII whitespace is sometimes essential for keeping control characters such as x0b, x0c, x1c, x1d, x1e, x1f.


About \s:

For Unicode (str) patterns: Matches Unicode whitespace characters (which includes [ \t\n\r\f\v], and also many other characters, for example the non-breaking spaces mandated by typography rules in many languages). If the ASCII flag is used, only [ \t\n\r\f\v] is matched.

About re.ASCII:

Make \w, \W, \b, \B, \d, \D, \s and \S perform ASCII-only matching instead of full Unicode matching. This is only meaningful for Unicode patterns, and is ignored for byte patterns. Corresponds to the inline flag (?a).

strip() will remote any leading and trailing whitespaces.

Sequence contains more than one element

FYI you can also get this error if EF Migrations tries to run with no Db configured, for example in a Test Project.

Chased this for hours before I figured out that it was erroring on a query, but, not because of the query but because it was when Migrations kicked in to try to create the Db.

Code to loop through all records in MS Access

Found a good code with comments explaining each statement. Code found at - accessallinone

Sub DAOLooping()
On Error GoTo ErrorHandler

Dim strSQL As String
Dim rs As DAO.Recordset

strSQL = "tblTeachers"
'For the purposes of this post, we are simply going to make 
'strSQL equal to tblTeachers.
'You could use a full SELECT statement such as:
'SELECT * FROM tblTeachers (this would produce the same result in fact).
'You could also add a Where clause to filter which records are returned:
'SELECT * FROM tblTeachers Where ZIPPostal = '98052'
' (this would return 5 records)

Set rs = CurrentDb.OpenRecordset(strSQL)
'This line of code instantiates the recordset object!!! 
'In English, this means that we have opened up a recordset 
'and can access its values using the rs variable.

With rs

    If Not .BOF And Not .EOF Then
    'We don’t know if the recordset has any records, 
    'so we use this line of code to check. If there are no records 
    'we won’t execute any code in the if..end if statement.    

        'It is not necessary to move to the last record and then back 
        'to the first one but it is good practice to do so.

        While (Not .EOF)
        'With this code, we are using a while loop to loop 
        'through the records. If we reach the end of the recordset, .EOF 
        'will return true and we will exit the while loop.

            Debug.Print rs.Fields("teacherID") & " " & rs.Fields("FirstName")
            'prints info from fields to the immediate window

            'We need to ensure that we use .MoveNext, 
            'otherwise we will be stuck in a loop forever… 
            '(or at least until you press CTRL+Break)

    End If

    'Make sure you close the recordset...
End With

    Set rs = Nothing
    '..and set it to nothing
    Exit Sub
    Resume ExitSub
End Sub

Recordsets have two important properties when looping through data, EOF (End-Of-File) and BOF (Beginning-Of-File). Recordsets are like tables and when you loop through one, you are literally moving from record to record in sequence. As you move through the records the EOF property is set to false but after you try and go past the last record, the EOF property becomes true. This works the same in reverse for the BOF property.

These properties let us know when we have reached the limits of a recordset.

How to export the Html Tables data into PDF using Jspdf

There is a tablePlugin for jspdf it expects array of objects and displays that data as a table. You can style the text and headers with little changes in the code. It is open source and also has examples for you to get started with.

Retrieve only the queried element in an object array in MongoDB collection

Although the question was asked 9.6 years ago, this has been of immense help to numerous people, me being one of them. Thank you everyone for all your queries, hints and answers. Picking up from one of the answers here.. I found that the following method can also be used to project other fields in the parent document.This may be helpful to someone.

For the following document, the need was to find out if an employee (emp #7839) has his leave history set for the year 2020. Leave history is implemented as an embedded document within the parent Employee document.

db.employees.find( {"leave_history.calendar_year": 2020}, 
    {leave_history: {$elemMatch: {calendar_year: 2020}},empno:true,ename:true}).pretty()

        "_id" : ObjectId("5e907ad23997181dde06e8fc"),
        "empno" : 7839,
        "ename" : "KING",
        "mgrno" : 0,
        "hiredate" : "1990-05-09",
        "sal" : 100000,
        "deptno" : {
                "_id" : ObjectId("5e9065f53997181dde06e8f8")
        "username" : "none",
        "password" : "none",
        "is_admin" : "N",
        "is_approver" : "Y",
        "is_manager" : "Y",
        "user_role" : "AP",
        "admin_approval_received" : "Y",
        "active" : "Y",
        "created_date" : "2020-04-10",
        "updated_date" : "2020-04-10",
        "application_usage_log" : [
                        "logged_in_as" : "AP",
                        "log_in_date" : "2020-04-10"
                        "logged_in_as" : "EM",
                        "log_in_date" : ISODate("2020-04-16T07:28:11.959Z")
        "leave_history" : [
                        "calendar_year" : 2020,
                        "pl_used" : 0,
                        "cl_used" : 0,
                        "sl_used" : 0
                        "calendar_year" : 2021,
                        "pl_used" : 0,
                        "cl_used" : 0,
                        "sl_used" : 0

Requested registry access is not allowed

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

What is the difference between java and core java?

A simple step to understand what is java and core java.

  • Find a book for Java.

  • Find a book for core java.

  • Compare the content of both books.

Actual result: both have almost same content.

Result: Java and core java is same.

core java is just slang, to emphasize on deep knowledge of basic java. but if I say I know Java it doesn't mean that I don't have deep knowledge of basic java, or if I know everything in java.

Git push won't do anything (everything up-to-date)

This happened to me when I ^C in the middle of a git push to GitHub. GitHub did not show that the changes had been made, however.

To fix it, I made a change to my working tree, committed, and then pushed again. It worked perfectly fine.

CSS 3 slide-in from left transition

Use CSS3 2D transform to avoid performance issues (mobile)

A common pitfall is to animate left/top/right/bottom properties instead of using to achieve the same effect. For a variety of reasons, the semantics of transforms make them easier to offload, but left/top/right/bottom are much more difficult.

Source: Mozilla Developer Network (MDN)


var $slider = document.getElementById('slider');
var $toggle = document.getElementById('toggle');

$toggle.addEventListener('click', function() {
    var isOpen = $slider.classList.contains('slide-in');

    $slider.setAttribute('class', isOpen ? 'slide-out' : 'slide-in');
#slider {
    position: absolute;
    width: 100px;
    height: 100px;
    background: blue;
    transform: translateX(-100%);
    -webkit-transform: translateX(-100%);

.slide-in {
    animation: slide-in 0.5s forwards;
    -webkit-animation: slide-in 0.5s forwards;

.slide-out {
    animation: slide-out 0.5s forwards;
    -webkit-animation: slide-out 0.5s forwards;
@keyframes slide-in {
    100% { transform: translateX(0%); }

@-webkit-keyframes slide-in {
    100% { -webkit-transform: translateX(0%); }
@keyframes slide-out {
    0% { transform: translateX(0%); }
    100% { transform: translateX(-100%); }

@-webkit-keyframes slide-out {
    0% { -webkit-transform: translateX(0%); }
    100% { -webkit-transform: translateX(-100%); }
<div id="slider" class="slide-in">

<button id="toggle" style="position:absolute; top: 120px;">Toggle</button>

Stripping everything but alphanumeric chars from a string in Python

sent = "".join(e for e in sent if e.isalpha())

How to add new elements to an array?

If one really want to resize an array you could do something like this:

String[] arr = {"a", "b", "c"};
// Output is: [a, b, c]

arr = Arrays.copyOf(arr, 10); // new size will be 10 elements
arr[3] = "d";
arr[4] = "e";
arr[5] = "f";

// Output is: [a, b, c, d, e, f, null, null, null, null]

How to convert a date to milliseconds

The 2017 answer is: Use the date and time classes introduced in Java 8 (and also backported to Java 6 and 7 in the ThreeTen Backport).

If you want to interpret the date-time string in the computer’s time zone:

    long millisSinceEpoch = LocalDateTime.parse(myDate, DateTimeFormatter.ofPattern("uuuu/MM/dd HH:mm:ss"))

If another time zone, fill that zone in instead of ZoneId.systemDefault(). If UTC, use

    long millisSinceEpoch = LocalDateTime.parse(myDate, DateTimeFormatter.ofPattern("uuuu/MM/dd HH:mm:ss"))

How to custom switch button?


     android:layout_height="wrap_content" />


<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="">

    <item android:state_checked="false"

    <item android:state_checked="true"



<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="">

    <item android:state_checked="false">
        <shape android:shape="rectangle">

            <size android:width="24dp" android:height="12dp" />
            <solid android:color="#EFE0BB" />
            <corners android:radius="6dp" />

    <item android:state_checked="true">

        <shape android:shape="rectangle">

            <size android:width="24dp" android:height="12dp" />
            <solid android:color="@color/colorPrimary" />
            <corners android:radius="6dp" />



<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="">

        <shape android:shape="oval">
            <solid android:color="#EFE0BB" />
                android:height="10dp" />
                android:color="@color/colorPrimary" />


<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="">

    <item >
        <shape android:shape="oval">
            <solid android:color="@color/colorPrimary"/>
            <size android:height="12dp"
            <stroke android:color="#EFE0BB"


issue ORA-00001: unique constraint violated coming in INSERT/UPDATE

Error message looks like this

Error message => ORA-00001: unique constraint (schema.unique_constraint_name) violated

ORA-00001 occurs when: "a query tries to insert a "duplicate" row in a table". It makes an unique constraint to fail, consequently query fails and row is NOT added to the table."


Find all columns used in unique_constraint, for instance column a, column b, column c, column d collectively creates unique_constraint and then find the record from source data which is duplicate, using following queries:

-- to find <<owner of the table>> and <<name of the table>> for unique_constraint

select *
where CONSTRAINT_NAME = '<unique_constraint_name>';

Then use Justin Cave's query (pasted below) to find all columns used in unique_constraint:

  SELECT column_name, position
  FROM all_cons_columns
  WHERE constraint_name = <<name of constraint from the error message>>
   AND owner           = <<owner of the table>>
   AND table_name      = <<name of the table>>

    -- to find duplicates

    select column a, column b, column c, column d
    from table
    group by column a, column b, column c, column d
    having count (<any one column used in constraint > ) > 1;

you can either delete that duplicate record from your source data (which was a select query in my particular case, as I experienced it with "Insert into select") or modify to make it unique or change the constraint.

How do I change button size in Python?

I've always used .place() for my tkinter widgets. place syntax

You can specify the size of it just by changing the keyword arguments!

Of course, you will have to call .place() again if you want to change it.

Works in python 3.8.2, if you're wondering.

Invalid default value for 'create_date' timestamp field

Using OS X, install mysql from Homebrew, System Variables based on its compiled-in defaults. Solution is to remove "NO_ZERO_DATE" from System Variables "sql_mode".

Just please keep in mind that scope involve.

If you want to affect only in your session, please use "@@session", For example:


In this case, it will not affect once your session ends or your change it. It has not effect on other session.

If you want to affect on all client, please use "@@global", for example:


In this case, it only affects on the clients that connect after the change(not affect on current all clients), and will not work once server exit.

Stripping non printable characters from a string in python

As far as I know, the most pythonic/efficient method would be:

import string

filtered_string = filter(lambda x: x in string.printable, myStr)

Android Lint contentDescription warning

Resolved this warning by setting attribute android:contentDescription for my ImageView


Android Lint support in ADT 16 throws this warning to ensure that image widgets provide a contentDescription.

This defines text that briefly describes content of the view. This property is used primarily for accessibility. Since some views do not have textual representation this attribute can be used for providing such.

Non-textual widgets like ImageViews and ImageButtons should use the contentDescription attribute to specify a textual description of the widget such that screen readers and other accessibility tools can adequately describe the user interface.

ASP.NET MVC - Find Absolute Path to the App_Data folder from Controller

string path = AppDomain.CurrentDomain.GetData("DataDirectory").ToString();

This is probably a more "correct" way of getting it.

How to define an enum with string value?

Maybe it's too late, but here it goes.

We can use the attribute EnumMember to manage Enum values.

public enum EUnitOfMeasure
    [EnumMember(Value = "KM")]
    [EnumMember(Value = "MI")]

This way the result value for EUnitOfMeasure will be KM or MI. This also can be seen in Andrew Whitaker answer.

How do I get the YouTube video ID from a URL?

I made a small function to extract the video id out of a Youtube url which can be seen below.

var videoId = function(url) {_x000D_
   var match = url.match(/v=([0-9a-z_-]{1,20})/i);_x000D_
   return (match ? match['1'] : false);_x000D_

This function will extract the video id even if there are multiple parameters in the url.

How to check Elasticsearch cluster health?

If Elasticsearch cluster is not accessible (e.g. behind firewall), but Kibana is:

Kibana => DevTools => Console:

GET /_cluster/health 

enter image description here enter image description here

How to make a class property?

def _create_type(meta, name, attrs):
    type_name = f'{name}Type'
    type_attrs = {}
    for k, v in attrs.items():
        if type(v) is _ClassPropertyDescriptor:
            type_attrs[k] = v
    return type(type_name, (meta,), type_attrs)

class ClassPropertyType(type):
    def __new__(meta, name, bases, attrs):
        Type = _create_type(meta, name, attrs)
        cls = super().__new__(meta, name, bases, attrs)
        cls.__class__ = Type
        return cls

class _ClassPropertyDescriptor(object):
    def __init__(self, fget, fset=None):
        self.fget = fget
        self.fset = fset

    def __get__(self, obj, owner):
        if self in obj.__dict__.values():
            return self.fget(obj)
        return self.fget(owner)

    def __set__(self, obj, value):
        if not self.fset:
            raise AttributeError("can't set attribute")
        return self.fset(obj, value)

    def setter(self, func):
        self.fset = func
        return self

def classproperty(func):
    return _ClassPropertyDescriptor(func)

class Bar(metaclass=ClassPropertyType):
    __bar = 1

    def bar(cls):
        return cls.__bar

    def bar(cls, value):
        cls.__bar = value

bar = Bar()
nbar = Bar()

Spring Boot, Spring Data JPA with multiple DataSources

here is my solution. base on spring-boot.1.2.5.RELEASE.

first.datasource.validation-query=select 1

second.datasource.validation-query=select 1

public class DataSourceConfig {
    public DataSource firstDataSource() {
        DataSource ds =  DataSourceBuilder.create().build();
        return ds;

    public DataSource secondDataSource() {
        DataSource ds =  DataSourceBuilder.create().build();
        return ds;

Convert Pandas DataFrame to JSON format

The output that you get after DF.to_json is a string. So, you can simply slice it according to your requirement and remove the commas from it too.

out = df.to_json(orient='records')[1:-1].replace('},{', '} {')

To write the output to a text file, you could do:

with open('file_name.txt', 'w') as f:

what does numpy ndarray shape do?

.shape() gives the actual shape of your array in terms of no of elements in it, No of rows/No of Columns. The answer you get is in the form of tuples.

For Example: 1D ARRAY:


Output: (4,) ie the number4 denotes the no of elements in the 1D Array.

2D Array:


Output: (2,3) ie the number of rows and the number of columns.

The number of elements in the final output will depend on the number of rows in the goes on increasing gradually.

Passing ArrayList through Intent

In your receiving intent you need to do:

Intent i = getIntent();  
stock_list = i.getStringArrayListExtra("stock_list");

The way you have it you've just created a new empty intent without any extras.

If you only have a single extra you can condense this down to:

stock_list = getIntent().getStringArrayListExtra("stock_list");

How do I set Tomcat Manager Application User Name and Password for NetBeans?

One simple way to check your changes to that file in Tomcat 8 + is to open a browser to: http://localhost:8080/manager/text/list

Getting HTTP code in PHP using curl

curl_getinfo — Get information regarding a specific transfer

Check curl_getinfo

// Create a curl handle
$ch = curl_init('');

// Execute

// Check if any error occurred
 $info = curl_getinfo($ch);

 echo 'Took ' . $info['total_time'] . ' seconds to send a request to ' . $info['url'];

// Close handle

html5 - canvas element - Multiple layers

but layer 02, will cover all drawings in layer 01. I used this to show drawing in both layers. use (background-color: transparent;) in style.

    <div style="position: relative;"> _x000D_
      <canvas id="lay01" width="500" height="500" style="position: absolute; left: 0; top: 0; z-index: 0; background-color: transparent;">_x000D_
      </canvas> _x000D_
      <canvas id="lay02" width="500" height="500" style="position: absolute; left: 0; top: 0; z-index: 1; background-color: transparent;">_x000D_

Import XXX cannot be resolved for Java SE standard classes

If the project is Maven, you can try this way :

  1. right click the "Maven Dependencies"-->"Build Path"-->"Remove from the build path";
  2. right click the project ,navigate to "Maven"--->"Update project....";

Then the import issue should be solved .

How to get response using cURL in PHP

If anyone else comes across this, I'm adding another answer to provide the response code or other information that might be needed in the "response".

// init curl object        
$ch = curl_init();

// define options
$optArray = array(
    CURLOPT_URL => '',

// apply those options
curl_setopt_array($ch, $optArray);

// execute request and get response
$result = curl_exec($ch);

// also get the error and response code
$errors = curl_error($ch);
$response = curl_getinfo($ch, CURLINFO_HTTP_CODE);




string(0) ""

// change to
string(42) "Could not resolve host:"

How to embed fonts in HTML?

I asked this a while back. The answer is basically that it doesn't work. :(

Getting error while sending email through Gmail SMTP - "Please log in via your web browser and then try again. 534-5.7.14"

There are two ways to resolve this, and only one may work, depending on how you're accessing Google.

The first method is to authorize access for your IP or client machine using the link. That can resolve authentication issues on client devices, like mobile or desktop apps. I would test this first, because it results in a lower overall decrease in account security.

If the above link doesn't work, it's because the session is being initiated by an app or device that is not associated with your particular location. Examples include:

  • An app that uses a remote server to retrieve data, like a web site or, in my case, other Google servers
  • A company mail server fetching mail on your behalf

In all such cases you have to use the link referenced above.

TLDR; check the captcha link first, and if it doesn't work, try the other one and enable less secure apps.

Normalizing a list of numbers in Python

If working with data, many times pandas is the simple key

This particular code will put the raw into one column, then normalize by column per row. (But we can put it into a row and do it by row per column, too! Just have to change the axis values where 0 is for row and 1 is for column.)

import pandas as pd

raw = [0.07, 0.14, 0.07]  

raw_df = pd.DataFrame(raw)
normed_df = raw_df.div(raw_df.sum(axis=0), axis=1)

where normed_df will display like:

0   0.25
1   0.50
2   0.25

and then can keep playing with the data, too!

Selecting multiple columns/fields in MySQL subquery

Yes, you can do this. The knack you need is the concept that there are two ways of getting tables out of the table server. One way is ..


The other way is

FROM (SELECT col as name1, col2 as name2 FROM ...) B

Notice that the select clause and the parentheses around it are a table, a virtual table.

So, using your second code example (I am guessing at the columns you are hoping to retrieve here):

SELECT a.attr,, b.trans, b.lang
FROM attribute a
 SELECT AS id, at.translation AS trans, at.language AS lang, a.attribute
 FROM attributeTranslation at
) b ON ( = b.attribute AND b.lang = 1)

Notice that your real table attribute is the first table in this join, and that this virtual table I've called b is the second table.

This technique comes in especially handy when the virtual table is a summary table of some kind. e.g.

SELECT a.attr,, b.trans, b.lang, c.langcount
FROM attribute a
 SELECT AS id, at.translation AS trans, at.language AS lang, at.attribute
 FROM attributeTranslation at
) b ON ( = b.attribute AND b.lang = 1)
 SELECT count(*) AS langcount,  at.attribute
 FROM attributeTranslation at
 GROUP BY at.attribute
) c ON ( = c.attribute)

See how that goes? You've generated a virtual table c containing two columns, joined it to the other two, used one of the columns for the ON clause, and returned the other as a column in your result set.

Filter Linq EXCEPT on properties

public static class ExceptByProperty
    public static List<T> ExceptBYProperty<T, TProperty>(this List<T> list, List<T> list2, Expression<Func<T, TProperty>> propertyLambda)
        Type type = typeof(T);

        MemberExpression member = propertyLambda.Body as MemberExpression;

        if (member == null)
            throw new ArgumentException(string.Format(
                "Expression '{0}' refers to a method, not a property.",

        PropertyInfo propInfo = member.Member as PropertyInfo;
        if (propInfo == null)
            throw new ArgumentException(string.Format(
                "Expression '{0}' refers to a field, not a property.",

        if (type != propInfo.ReflectedType &&
            throw new ArgumentException(string.Format(
                "Expresion '{0}' refers to a property that is not from type {1}.",
        Func<T, TProperty> func = propertyLambda.Compile();
        var ids = list2.Select<T, TProperty>(x => func(x)).ToArray();
        return list.Where(i => !ids.Contains(((TProperty)propInfo.GetValue(i, null)))).ToList();

public class testClass
    public int ID { get; set; }
    public string Name { get; set; }

For Test this:

        List<testClass> a = new List<testClass>();
        List<testClass> b = new List<testClass>();
        a.Add(new testClass() { ID = 1 });
        a.Add(new testClass() { ID = 2 });
        a.Add(new testClass() { ID = 3 });
        a.Add(new testClass() { ID = 4 });
        a.Add(new testClass() { ID = 5 });

        b.Add(new testClass() { ID = 3 });
        b.Add(new testClass() { ID = 5 });
        a.Select<testClass, int>(x => x.ID);

        var items = a.ExceptBYProperty(b, u => u.ID);

How to get user agent in PHP

You could also use the php native funcion get_browser()

IMPORTANT NOTE: You should have a browscap.ini file.

CSS media query to target iPad and iPad only?

    <title>orientation and device detection in css3</title>

    <link rel="stylesheet" media="all and (max-device-width: 480px) and (orientation:portrait)" href="iphone-portrait.css" />
    <link rel="stylesheet" media="all and (max-device-width: 480px) and (orientation:landscape)" href="iphone-landscape.css" />
    <link rel="stylesheet" media="all and (device-width: 768px) and (device-height: 1024px) and (orientation:portrait)" href="ipad-portrait.css" />
    <link rel="stylesheet" media="all and (device-width: 768px) and (device-height: 1024px) and (orientation:landscape)" href="ipad-landscape.css" />
    <link rel="stylesheet" media="all and (device-width: 800px) and (device-height: 1184px) and (orientation:portrait)" href="htcdesire-portrait.css" />
    <link rel="stylesheet" media="all and (device-width: 800px) and (device-height: 390px) and (orientation:landscape)" href="htcdesire-landscape.css" />
    <link rel="stylesheet" media="all and (min-device-width: 1025px)" href="desktop.css" />

    <div id="iphonelandscape">iphone landscape</div>
    <div id="iphoneportrait">iphone portrait</div>
    <div id="ipadlandscape">ipad landscape</div>
    <div id="ipadportrait">ipad portrait</div>
    <div id="htcdesirelandscape">htc desire landscape</div>
    <div id="htcdesireportrait">htc desire portrait</div>
    <div id="desktop">desktop</div>
    <script type="text/javascript">
        function res() { document.write(screen.width + ', ' + screen.height); }

C++ templates that accept only certain types

This typically is unwarranted in C++, as other answers here have noted. In C++ we tend to define generic types based on other constraints other than "inherits from this class". If you really wanted to do that, it's quite easy to do in C++11 and <type_traits>:

#include <type_traits>

template<typename T>
class observable_list {
    static_assert(std::is_base_of<list, T>::value, "T must inherit from list");
    // code here..

This breaks a lot of the concepts that people expect in C++ though. It's better to use tricks like defining your own traits. For example, maybe observable_list wants to accept any type of container that has the typedefs const_iterator and a begin and end member function that returns const_iterator. If you restrict this to classes that inherit from list then a user who has their own type that doesn't inherit from list but provides these member functions and typedefs would be unable to use your observable_list.

There are two solutions to this issue, one of them is to not constrain anything and rely on duck typing. A big con to this solution is that it involves a massive amount of errors that can be hard for users to grok. Another solution is to define traits to constrain the type provided to meet the interface requirements. The big con for this solution is that involves extra writing which can be seen as annoying. However, the positive side is that you will be able to write your own error messages a la static_assert.

For completeness, the solution to the example above is given:

#include <type_traits>

struct void_ {
    using type = void;

template<typename... Args>
using Void = typename void_<Args...>::type;

template<typename T, typename = void>
struct has_const_iterator : std::false_type {};

template<typename T>
struct has_const_iterator<T, Void<typename T::const_iterator>> : std::true_type {};

struct has_begin_end_impl {
    template<typename T, typename Begin = decltype(std::declval<const T&>().begin()),
                         typename End   = decltype(std::declval<const T&>().end())>
    static std::true_type test(int);
    static std::false_type test(...);

template<typename T>
struct has_begin_end : decltype(has_begin_end_impl::test<T>(0)) {};

template<typename T>
class observable_list {
    static_assert(has_const_iterator<T>::value, "Must have a const_iterator typedef");
    static_assert(has_begin_end<T>::value, "Must have begin and end member functions");
    // code here...

There are a lot of concepts shown in the example above that showcase C++11's features. Some search terms for the curious are variadic templates, SFINAE, expression SFINAE, and type traits.

Skipping every other element after the first

def altElement(a):
    return a[::2]

How can I use Timer (formerly NSTimer) in Swift?

You will need to use Timer instead of NSTimer in Swift 3.

Here is an example:

Timer.scheduledTimer(timeInterval: 1, 
    target: self, 
    selector: #selector(YourController.update), 
    userInfo: nil, 
    repeats: true)

// @objc selector expected for Timer
@objc func update() {
    // do what should happen when timer triggers an event

Better way to check if a Path is a File or a Directory?

I needed this, the posts helped, this gets it down to one line, and if the path isn't a path at all, it just returns and exits the method. It addresses all of the above concerns, doesn't need the trailing slash either.

if (!Directory.Exists(@"C:\folderName")) return;

Windows 7, 64 bit, DLL problems

This contribution does not really answer the initial question, but taking into account the hit-rate of this thread I assume that there are quite a few people dealing with the problem that API-MS-WIN-CORE- libraries cannot be found.

I was able to solve a problem where my application refused to start with the error message that API-MS-WIN-CORE-WINRT-STRING-L1-1-0.DLL is not found by simply updating Visual Studio.

I don't think that my build environment (Windows 7 Pro SP1, Visual Studio Ultimate 2012) was messed up completely, it worked fine for most of my projects. But under some very specific circumstances I got the error message (see below).

After updating Visual Studio 11 from the initial CD-Version (I forgot to look up the version number) to version 11.0.61030.00 Update 4 also the broken project was running again.

Error message at application startup

Converting pfx to pem using openssl

You can use the OpenSSL Command line tool. The following commands should do the trick

openssl pkcs12 -in client_ssl.pfx -out client_ssl.pem -clcerts

openssl pkcs12 -in client_ssl.pfx -out root.pem -cacerts

If you want your file to be password protected etc, then there are additional options.

You can read the entire documentation here.

How to get element-wise matrix multiplication (Hadamard product) in numpy?

import numpy as np
x = np.array([[1,2,3], [4,5,6]])
y = np.array([[-1, 2, 0], [-2, 5, 1]])

array([[-1,  4,  0],
       [-8, 25,  6]])

%timeit x*y
1000000 loops, best of 3: 421 ns per loop

array([[-1,  4,  0],
       [-8, 25,  6]])

%timeit np.multiply(x, y)
1000000 loops, best of 3: 457 ns per loop

Both np.multiply and * would yield element wise multiplication known as the Hadamard Product

%timeit is ipython magic

Get connection string from App.config

I had the same Issue. my solution was built up from two projects. A Class library and a website referencing to the class library project. the problem was that i was trying to access the App.config in my Class library project but the system was searching in Web.config of the website. I put the connection string inside Web.config and ... problem solved!

The main reason was that despite ConfigurationManager was used in another assembly it was searching inside the runnig project .

jquery - fastest way to remove all rows from a very large table

$("#myTable > tbody").empty();

It won't touch the headers.