Programs & Examples On #Rmysql

An R package for interfacing with MySQL and MariaDB databases.

Spring Boot Multiple Datasource

once you start work with jpa and some driver is in your class path spring boot right away puts it inside as your data source (e.g h2 ) for using the defult data source therefore u will need only to define

spring.datasource.url= jdbc:mysql://localhost:3306/

if we go one step farther and u want to use two I would reccomend to use two data sources such as explained here : Spring Boot Configure and Use Two DataSources

How to select a CRAN mirror in R

I had, on macOS, the exact thing that you say: A 'please select' prompt and then nothing more.

After I opened (and updated; don't know if that was relevant) X-Quartz, and then restarted R and tried again, I got an X-window list of mirrors to choose from after a few seconds. It was faster the third time onwards.

Write to file, but overwrite it if it exists

Despite NylonSmile's answer, which is "sort of" correct.. I was unable to overwrite files, in this manner..

echo "i know about Pipes, girlfriend" > thatAnswer

zsh: file exists: thatAnswer

to solve my issues.. I had to use... >!, á la..

[[ $FORCE_IT == 'YES' ]] && echo "$@" >! "$X" || echo "$@" > "$X"

Obviously, be careful with this...

Looping over a list in Python

Here is the solution I was looking for. If you would like to create List2 that contains the difference of the number elements in List1.

list1 = [12, 15, 22, 54, 21, 68, 9, 73, 81, 34, 45]
list2 = []
for i in range(1, len(list1)):
  change = list1[i] - list1[i-1]

Note that while len(list1) is 11 (elements), len(list2) will only be 10 elements because we are starting our for loop from element with index 1 in list1 not from element with index 0 in list1

Get Current date & time with [NSDate date]

NSLocale* currentLocale = [NSLocale currentLocale];
[[NSDate date] descriptionWithLocale:currentLocale];  

or use

NSDateFormatter *dateFormatter=[[NSDateFormatter alloc] init]; 
[dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
// or @"yyyy-MM-dd hh:mm:ss a" if you prefer the time with AM/PM 
NSLog(@"%@",[dateFormatter stringFromDate:[NSDate date]]);

Why is "throws Exception" necessary when calling a function?

If you propagate the exception by declaring the throws directive in the signature of the current method, then somewhere up the line or call stack a try/catch construct must be used to handle the exception.

Proper way to set response status and JSON content in a REST API made with nodejs and express

status of 200 will be the default when using res.send, res.json, etc.

You can set the status like res.status(500).json({ error: 'something is wrong' });

Often I'll do something like...

router.get('/something', function(req, res, next) {
  // Some stuff here
  if(err) {
    return next(err);
  // More stuff here

Then have my error middleware send the response, and do anything else I need to do when there is an error.

Additionally: res.sendStatus(status) has been added as of version 4.9.0

What is the meaning of {...this.props} in Reactjs

You will use props in your child component

for example

if your now component props is

   booking: 4,
   isDisable: false

you can use this props in your child compoenet

 <div {...this.props}> ... </div>

in you child component, you will receive all your parent props.

WPF Data Binding and Validation Rules Best Practices

If your business class is directly used by your UI is preferrable to use IDataErrorInfo because it put logic closer to their owner.

If your business class is a stub class created by a reference to an WCF/XmlWeb service then you can not/must not use IDataErrorInfo nor throw Exception for use with ExceptionValidationRule. Instead you can:

  • Use custom ValidationRule.
  • Define a partial class in your WPF UI project and implements IDataErrorInfo.

SQL Server: How to check if CLR is enabled?

Check the config_value in the results of sp_configure

You can enable CLR by running the following:

sp_configure 'show advanced options', 1;
sp_configure 'clr enabled', 1;

MSDN Article on enabling CLR

MSDN Article on sp_configure

How do I clear the previous text field value after submitting the form with out refreshing the entire page?

you can just do as you get that elements value


How do I delete multiple rows in Entity Framework (without foreach)

I know it's quite late but in case someone needs a simple solution, the cool thing is you can also add the where clause with it:

public static void DeleteWhere<T>(this DbContext db, Expression<Func<T, bool>> filter) where T : class
    string selectSql = db.Set<T>().Where(filter).ToString();
    string fromWhere = selectSql.Substring(selectSql.IndexOf("FROM"));
    string deleteSql = "DELETE [Extent1] " + fromWhere;

Note: just tested with MSSQL2008.


The solution above won't work when EF generates sql statement with parameters, so here's the update for EF5:

public static void DeleteWhere<T>(this DbContext db, Expression<Func<T, bool>> filter) where T : class
    var query = db.Set<T>().Where(filter);

    string selectSql = query.ToString();
    string deleteSql = "DELETE [Extent1] " + selectSql.Substring(selectSql.IndexOf("FROM"));

    var internalQuery = query.GetType().GetFields(BindingFlags.NonPublic | BindingFlags.Instance).Where(field => field.Name == "_internalQuery").Select(field => field.GetValue(query)).First();
    var objectQuery = internalQuery.GetType().GetFields(BindingFlags.NonPublic | BindingFlags.Instance).Where(field => field.Name == "_objectQuery").Select(field => field.GetValue(internalQuery)).First() as ObjectQuery;
    var parameters = objectQuery.Parameters.Select(p => new SqlParameter(p.Name, p.Value)).ToArray();

    db.Database.ExecuteSqlCommand(deleteSql, parameters);

It requires a little bit of reflection but works well.

LaTex left arrow over letter in math mode

Use \overleftarrow to create a long arrow to the left.


LaTeX output

Mockito : how to verify method was called on an object created within a method?

The classic response is, "You don't." You test the public API of Foo, not its internals.

Is there any behavior of the Foo object (or, less good, some other object in the environment) that is affected by foo()? If so, test that. And if not, what does the method do?

Force IE8 Into IE7 Compatiblity Mode

its even simpler than that. Using HTML you can just add this metatag to your page (first thing on the page):

<meta http-equiv="X-UA-Compatible" content="IE=7" />

If you wanted to do it, you just have to send your http request with that meta information in the header. This would require a page refresh to work though.

Also, you can look at a similar question here: Compatibility Mode in IE8 using VBScript

How to play .wav files with java

Shortest form (without having to install random libraries) ?

public static void play(String filename)
        Clip clip = AudioSystem.getClip(); File(filename)));
    catch (Exception exc)

The only problem is there is no good way to make this method blocking to close and dispose the data after *.wav finishes. clip.drain() says it's blocking but it's not. The clip isn't running RIGHT AFTER start(). The only working but UGLY way I found is:

// ...
while (!clip.isRunning())
while (clip.isRunning())

How to retrieve all keys (or values) from a std::map and put them into a vector?

Your solution is fine but you can use an iterator to do it:

std::map<int, int> m;
m.insert(std::pair<int, int>(3, 4));
m.insert(std::pair<int, int>(5, 6));
for(std::map<int, int>::const_iterator it = m.begin(); it != m.end(); it++)
    int key = it->first;
    int value = it->second;
    //Do something

What do <o:p> elements do anyway?

Couldn't find any official documentation (no surprise there) but according to this interesting article, those elements are injected in order to enable Word to convert the HTML back to fully compatible Word document, with everything preserved.

The relevant paragraph:

Microsoft added the special tags to Word's HTML with an eye toward backward compatibility. Microsoft wanted you to be able to save files in HTML complete with all of the tracking, comments, formatting, and other special Word features found in traditional DOC files. If you save a file in HTML and then reload it in Word, theoretically you don't loose anything at all.

This makes lots of sense.

For your specific question.. the o in the <o:p> means "Office namespace" so anything following the o: in a tag means "I'm part of Office namespace" - in case of <o:p> it just means paragraph, the equivalent of the ordinary <p> tag.

I assume that every HTML tag has its Office "equivalent" and they have more.

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

It took a while to find the right combination, but this seems to center the overlay or popup content, both horizontally and vertically, without prior knowledge of the content height:


<div class="overlayShadow">
    <div class="overlayBand">
        <div class="overlayBox">
            Your content


.overlayShadow {
    display: table;
    position: fixed;
    left: 0px;
    top: 0px;
    width: 100%;
    height: 100%;
    background-color: rgba(0, 0, 0, 0.75);
    z-index: 20;

.overlayBand {
    display: table-cell;
    vertical-align: middle;

.overlayBox {
    display: table;
    margin: 0 auto 0 auto;
    width: 600px; /* or whatever */
    background-color: white; /* or whatever */

How to compare dates in datetime fields in Postgresql?

When you compare update_date >= '2013-05-03' postgres casts values to the same type to compare values. So your '2013-05-03' was casted to '2013-05-03 00:00:00'.

So for update_date = '2013-05-03 14:45:00' your expression will be that:

'2013-05-03 14:45:00' >= '2013-05-03 00:00:00' AND '2013-05-03 14:45:00' <= '2013-05-03 00:00:00'

This is always false

To solve this problem cast update_date to date:

select * from table where update_date::date >= '2013-05-03' AND update_date::date <= '2013-05-03' -> Will return result

How do I get the directory of the PowerShell script I execute?

PowerShell 3 has the $PSScriptRoot automatic variable:

Contains the directory from which a script is being run.

In Windows PowerShell 2.0, this variable is valid only in script modules (.psm1). Beginning in Windows PowerShell 3.0, it is valid in all scripts.

Don't be fooled by the poor wording. PSScriptRoot is the directory of the current file.

In PowerShell 2, you can calculate the value of $PSScriptRoot yourself:

# PowerShell v2
$PSScriptRoot = Split-Path -Parent -Path $MyInvocation.MyCommand.Definition

JavaScript: Object Rename Key

Here is an example to create a new object with renamed keys.

let x = { id: "checkout", name: "git checkout", description: "checkout repository" };

let renamed = Object.entries(x).reduce((u, [n, v]) => {
  u[`__${n}`] = v;
  return u;
}, {});

Ignore outliers in ggplot2 boxplot

Here is a solution using boxplot.stats

# create a dummy data frame with outliers
df = data.frame(y = c(-100, rnorm(100), 100))

# create boxplot that includes outliers
p0 = ggplot(df, aes(y = y)) + geom_boxplot(aes(x = factor(1)))

# compute lower and upper whiskers
ylim1 = boxplot.stats(df$y)$stats[c(1, 5)]

# scale y limits based on ylim1
p1 = p0 + coord_cartesian(ylim = ylim1*1.05)

mongoError: Topology was destroyed

It seems to mean your node server's connection to your MongoDB instance was interrupted while it was trying to write to it.

Take a look at the Mongo source code that generates that error

Mongos.prototype.insert = function(ns, ops, options, callback) {
    if(typeof options == 'function') callback = options, options = {};
    if(this.s.state == DESTROYED) return callback(new MongoError(f('topology was destroyed')));
    // Topology is not connected, save the call in the provided store to be
    // Executed at some point when the handler deems it's reconnected
    if(!this.isConnected() && this.s.disconnectHandler != null) {
      callback = bindToCurrentDomain(callback);
      return this.s.disconnectHandler.add('insert', ns, ops, options, callback);

    executeWriteOperation(this.s, 'insert', ns, ops, options, callback);

This does not appear to be related to the Sails issue cited in the comments, as no upgrades were installed to precipitate the crash or the "fix"

Hive ParseException - cannot recognize input near 'end' 'string'

You can always escape the reserved keyword if you still want to make your query work!!

Just replace end with `end`

Here is the list of reserved keywords

CREATE EXTERNAL TABLE moveProjects (cid string, `end` string, category string)
STORED BY 'org.apache.hadoop.hive.dynamodb.DynamoDBStorageHandler'
TBLPROPERTIES ("" = "Projects",
    "dynamodb.column.mapping" = "cid:cid,end:end,category:category");

"unrecognized import path" with go get

The issues are relating to an invalid GOROOT.

I think you installed Go in /usr/local/go.
So change your GOROOT path to the value of /usr/local/go/bin.

It seems that you meant to have your workspace (GOPATH) located at /home/me/go.

This might fix your problem.
Add this to the bottom of your bash profile, located here => $HOME/.profile

export GOROOT=/usr/local/go
export GOPATH=$HOME/go
export PATH=$PATH:$GOROOT/bin

Make sure to remove the old references of GOROOT.

Then try installing web.go again.

If that doesn't work, then have Ubuntu install Go for you.

sudo apt-get install golang

Video tutorial:

Convert decimal to binary in python

def dec_to_bin(x):
    return int(bin(x)[2:])

It's that easy.

form serialize javascript (no framework)

I started with the answer from Johndave Decano.

This should fix a few of the issues mentioned in replies to his function.

  1. Replace %20 with a + symbol.
  2. Submit/Button types will only be submitted if they were clicked to submit the form.
  3. Reset buttons will be ignored.
  4. The code seemed redundant to me since it is doing essentially the same thing regardless of the field types. Not to mention incompatibility with HTML5 field types such as 'tel' and 'email', thus I removed most of the specifics with the switch statements.

Button types will still be ignored if they don't have a name value.

function serialize(form, evt){
    var evt    = evt || window.event; = || evt.srcElement || null;
    var field, query='';
    if(typeof form == 'object' && form.nodeName == "FORM"){
        for(i=form.elements.length-1; i>=0; i--){
            field = form.elements[i];
            if( && field.type != 'file' && field.type != 'reset'){
                if(field.type == 'select-multiple'){
                    for(j=form.elements[i].options.length-1; j>=0; j--){
                            query += '&' + + "=" + encodeURIComponent(field.options[j].value).replace(/%20/g,'+');
                    if((field.type != 'submit' && field.type != 'button') || == field){
                        if((field.type != 'checkbox' && field.type != 'radio') || field.checked){
                            query += '&' + + "=" + encodeURIComponent(field.value).replace(/%20/g,'+');
    return query.substr(1);

This is how I am currently using this function.

<form onsubmit="myAjax('', 'POST', serialize(this, event))">

How to programmatically turn off WiFi on Android device?

You need the following permissions in your manifest file:

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

Then you can use the following in your activity class:

WifiManager wifiManager = (WifiManager) this.getApplicationContext().getSystemService(Context.WIFI_SERVICE); 

Use the following to check if it's enabled or not

boolean wifiEnabled = wifiManager.isWifiEnabled()

You'll find a nice tutorial on the subject on this site.

VBA - Select columns using numbers?

no need for loops or such.. try this..

dim startColumnas integer

dim endColumn as integer

startColumn = 7

endColumn = 24

Range(Cells(, startColumn), Cells(, endColumn)).ColumnWidth = 3.8 ' <~~ whatever width you want to set..* 

The HTTP request is unauthorized with client authentication scheme 'Ntlm'. The authentication header received from the server was 'Negotiate,NTLM'

You can eliminate the client from the problem by using wftech, this is an old tool but I have found it useful in diagnosing authentication issues. wfetch allows you to specify NTLM, Negotiate and kerberos, this may well help you better understand your problem. As you are trying to call a service and wfetch knows nothing about WCF, I would suggest applying your endpoint binding (PROVIDERSSoapBinding) to the serviceMetadata then you can do an HTTP GET of the WSDL for the service with the same security settings.

Another option, which may be available to you is to force the server to use NTLM, you can do this by either editing the metabase (IIS 6) and removing the Negotiate setting, more details at

If you are using IIS 7.x then the approach is slightly different, details of how to configure the authentication providers are here

I notice that you have blocked out the server address with, so I'm guessing that this is an IP address rather than a server name, this may cause issues with authentication, so if possible try targeting the machine name.

Sorry that I haven't given you the answer but rather pointers for getting closer to the issue, but I hope it helps.

I'll finish by saying that I have experienced this same issue and my only recourse was to use Kerberos rather than NTLM, don't forget you'll need to register an SPN for the service if you do go down this route.

Read properties file outside JAR file

I have a similar case: wanting my *.jar file to access a file in a directory next to said *.jar file. Refer to THIS ANSWER as well.

My file structure is:

./ - the root of your program
|__ *.jar
|__ dir-next-to-jar/some.txt

I'm able to load a file (say, some.txt) to an InputStream inside the *.jar file with the following:

InputStream stream = null;
        stream = ThisClassName.class.getClass().getResourceAsStream("/dir-next-to-jar/some.txt");
    catch(Exception e) {
        System.out.print("error file to stream: ");

Then do whatever you will with the stream

How to delete a workspace in Eclipse?

Just go to the \eclipse-java-helios-SR2-win32\eclipse\configuration.settings directory and change or remove org.eclipse.ui.ide.prefs file.

Naming Conventions: What to name a boolean variable?

How about:

 or isFollowedBySiblings (or isFolloedByItems, or isFollowedByOtherItems etc.)
 or moreItems

Although I think that even though you shouldn't make a habit of braking 'the rules' sometimes the best way to accomplish something may be to make an exception of the rule (Code Complete guidelines), and in your case, name the variable isNotLast

What is the IntelliJ shortcut key to create a javadoc comment?

Typing /** + then pressing Enter above a method signature will create Javadoc stubs for you.

Programmatically saving image to Django ImageField

class tweet_photos(models.Model):
upload_path='absolute path'
image_url = models.URLField(null=True, blank=True)
def save(self, *args, **kwargs):
    if self.image_url:
        import urllib, os
        from urlparse import urlparse
        file_save_dir = self.upload_path
        filename = urlparse(self.image_url).path.split('/')[-1]
        urllib.urlretrieve(self.image_url, os.path.join(file_save_dir, filename))
        self.image = os.path.join(file_save_dir, filename)
        self.image_url = ''
    super(tweet_photos, self).save()

Error: Specified cast is not valid. (SqlManagerUI)

This would also happen when you are trying to restore a newer version backup in a older SQL database. For example when you try to restore a DB backup that is created in 2012 with 110 compatibility and you are trying to restore it in 2008 R2.

How to remove padding around buttons in Android?

My solution was set to 0 the insetTop and insetBottom properties.


Datatables on-the-fly resizing

I got this to work as follows:

First ensure that in your dataTable definition your aoColumns array includes sWidth data expressed as a % not fixed pixels or ems. Then ensure you have set the bAutoWidth property to false Then add this little but of JS:

update_table_size = function(a_datatable) {
  if (a_datatable == null) return;
  var dtb;
  if (typeof a_datatable === 'string') dtb = $(a_datatable)
  else dtb = a_datatable;
  if (dtb == null) return;

  dtb.css('width', dtb.parent().width());

$(window).resize(function() {
  setTimeout(function(){update_table_size(some_table_selector_or_table_ref)}, 250);

Works a treat and my table cells handle the white-space: wrap; CSS (which wasn't working without setting the sWidth, and was what led me to this question.)

don't fail jenkins build if execute shell fails

There is another smooth way to tell Jenkins not to fail. You can isolate your commit in a build step and set the shell to not fail:

set +e
git commit -m "Bla."
set -e

Adding background image to div using CSS


.content {
    background: url('') center no-repeat;

.displaybg {
   text-align: center;
   color: #FFF;

Using sed, how do you print the first 'N' characters of a line?

To print the N first characters you can remove the N+1 characters up to the end of line:

$ sed 's/.//5g' <<< "defn-test"

You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '''')' at line 2

Please make sure you have downloaded the sqldump fully, this problem is very common when we try to import half/incomplete downloaded sqldump. Please check size of your sqldump file.

How to check Spark Version

According to the Cloudera documentation - What's New in CDH 5.7.0 it includes Spark 1.6.0.

Where's my JSON data in my incoming Django request?

Method 1

Client : Send as JSON

    url: '',
    type: 'POST',
    contentType: 'application/json; charset=utf-8',
    processData: false,
    data: JSON.stringify({'name':'John', 'age': 42}),

//Sent as a JSON object {'name':'John', 'age': 42}

Server :

data = json.loads(request.body) # {'name':'John', 'age': 42}

Method 2

Client : Send as x-www-form-urlencoded
(Note: contentType & processData have changed, JSON.stringify is not needed)

    url: '',
    type: 'POST',    
    data: {'name':'John', 'age': 42},
    contentType: 'application/x-www-form-urlencoded; charset=utf-8',  //Default
    processData: true,       

//Sent as a query string name=John&age=42

Server :

data = request.POST # will be <QueryDict: {u'name':u'John', u'age': 42}>

Changed in 1.5+ :

Non-form data in HTTP requests :
request.POST will no longer include data posted via HTTP requests with non form-specific content-types in the header. In prior versions, data posted with content-types other than multipart/form-data or application/x-www-form-urlencoded would still end up represented in the request.POST attribute. Developers wishing to access the raw POST data for these cases, should use the request.body attribute instead.

Probably related

Transparent image - background color

If I understand you right, you can do this:

<img src="image.png" style="background-color:red;" />

In fact, you can even apply a whole background-image to the image, resulting in two "layers" without the need for multi-background support in the browser ;)

Insert a string at a specific index

You can use Regular Expressions with a dynamic pattern.

var text = "something";
var output = "                    ";
var pattern = new RegExp("^\\s{"+text.length+"}");
var output.replace(pattern,text);


"something      "

This replaces text.length of whitespace characters at the beginning of the string output. The RegExp means ^\ - beginning of a line \s any white space character, repeated {n} times, in this case text.length. Use \\ to \ escape backslashes when building this kind of patterns out of strings.

No mapping found for HTTP request with URI.... in DispatcherServlet with name

If you want to serve .html files, you must add this <mvc:default-servlet-handler /> in your spring config file. .html files are static. Hope that this can help someone.

Using the "With Clause" SQL Server 2008

There are two types of WITH clauses:

Here is the FizzBuzz in SQL form, using a WITH common table expression (CTE).

;WITH mil AS (
 SELECT TOP 1000000 ROW_NUMBER() OVER ( ORDER BY c.column_id ) [n]
 FROM master.sys.all_columns as c
 CROSS JOIN master.sys.all_columns as c2
             CASE WHEN n  % 5 = 0 THEN 'FizzBuzz' ELSE 'Fizz' END
        WHEN n % 5 = 0 THEN 'Buzz'
        ELSE CAST(n AS char(6))
     END + CHAR(13)
 FROM mil

Here is a select statement also using a WITH clause

SELECT * FROM orders WITH (NOLOCK) where order_id = 123

Class vs. static method in JavaScript

There are tree ways methods and properties are implemented on function or class objects, and on they instances.

  1. On the class (or function) itself : Foo.method() or Foo.prop. Those are static methods or properties
  2. On its prototype : Foo.prototype.method() or Foo.prototype.prop. When created, the instances will inherit those object via the prototype witch is {method:function(){...}, prop:...}. So the foo object will receive, as prototype, a copy of the Foo.prototype object.
  3. On the instance itself : the method or property is added to the object itself. foo={method:function(){...}, prop:...}

The this keyword will represent and act differently according to the context. In a static method, it will represent the class itself (witch is after all an instance of Function : class Foo {} is quite equivalent to let Foo = new Function({})

With ECMAScript 2015, that seems well implemented today, it is clearer to see the difference between class (static) methods and properties, instance methods and properties and own methods ans properties. You can thus create three method or properties having the same name, but being different because they apply to different objects, the this keyword, in methods, will apply to, respectively, the class object itself and the instance object, by the prototype or by its own.

class Foo {
  static prop = "I am static" // see 1.
  static method(str) {alert("static method"+str+" :"+this.prop)} // see 1.
  prop="I am of an instance"; // see 2.
  method(str) {alert("instance method"+str+" : "+this.prop)} // see 2.

var foo= new Foo();
foo.prop = "I am of own";  // see 3.
foo.func = function(str){alert("own method" + str + this.prop)} // see 3.

Format Instant to String

public static void main(String[] args) {

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

    System.out.println(DATE_TIME_FORMATTER.format(new Date().toInstant()));


Get all files that have been modified in git branch

I can't believe there are so many ways to do this. I use whatchanged as someone posted before, just with the following arguments:

git whatchanged --name-only --pretty="" origin..HEAD

This just lists the filenames, and only the ones that changed on the current branch.

Removing element from array in component state

Here is a way to remove the element from the array in the state using ES6 spread syntax.

onRemovePerson: (index) => {
  const data =;
    data: [,index),]

C string append

man page of strcat says that arg1 and arg2 are appended to arg1.. and returns the pointer of s1. If you dont want disturb str1,str2 then you have write your own function.

char * my_strcat(const char * str1, const char * str2)
   char * ret = malloc(strlen(str1)+strlen(str2));

     sprintf(ret, "%s%s", str1, str2);
     return ret;
   return NULL;    

Hope this solves your purpose

The origin server did not find a current representation for the target resource or is not willing to disclose that one exists

the problem is in url pattern of servlet-mapping.


let's say our controller is

public class HomeController {
    public String home(){
        return "home";

when we hit some URL on our browser. the dispatcher servlet will try to map this url.

the url pattern of our serlvet currently is /Dispatcher which means resources are served from {contextpath}/Dispatcher

but when we request http://localhost:8080/home we are actually asking resources from / which is not available. so either we need to say dispatcher servlet to serve from / by doing


our make it serve from /Dispatcher by doing /Dispatcher/*


<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="" 
xsi:schemaLocation="" id="WebApp_ID" 



and request it with http://localhost:8080/Dispatcher/home or put just / to request like

http://localhost:8080/home :connection timed out: connect?

The error message says it all: your connection timed out. This means your request did not get a response within some (default) timeframe. The reasons that no response was received is likely to be one of:

  • a) The IP/domain or port is incorrect
  • b) The IP/domain or port (i.e service) is down
  • c) The IP/domain is taking longer than your default timeout to respond
  • d) You have a firewall that is blocking requests or responses on whatever port you are using
  • e) You have a firewall that is blocking requests to that particular host
  • f) Your internet access is down

Note that firewalls and port or IP blocking may be in place by your ISP

How to check if a table contains an element in Lua?

Given your representation, your function is as efficient as can be done. Of course, as noted by others (and as practiced in languages older than Lua), the solution to your real problem is to change representation. When you have tables and you want sets, you turn tables into sets by using the set element as the key and true as the value. +1 to interjay.

The resource could not be loaded because the App Transport Security policy requires the use of a secure connection

In Swift 4 You can use

->Go Info.plist

-> Click plus of Information properties list

->Add App Transport Security Settings as dictionary

-> Click Plus icon App Transport Security Settings

-> Add Allow Arbitrary Loads set YES

Bellow image look like

enter image description here

"While .. End While" doesn't work in VBA?

While constructs are terminated not with an End While but with a Wend.

While counter < 20
    counter = counter + 1

Note that this information is readily available in the documentation; just press F1. The page you link to deals with Visual Basic .NET, not VBA. While (no pun intended) there is some degree of overlap in syntax between VBA and VB.NET, one can't just assume that the documentation for the one can be applied directly to the other.

Also in the VBA help file:

Tip The Do...Loop statement provides a more structured and flexible way to perform looping.

how to implement login auth in node.js

Here's how I do it with Express.js:

1) Check if the user is authenticated: I have a middleware function named CheckAuth which I use on every route that needs the user to be authenticated:

function checkAuth(req, res, next) {
  if (!req.session.user_id) {
    res.send('You are not authorized to view this page');
  } else {

I use this function in my routes like this:

app.get('/my_secret_page', checkAuth, function (req, res) {
  res.send('if you are viewing this page it means you are logged in');

2) The login route:'/login', function (req, res) {
  var post = req.body;
  if (post.user === 'john' && post.password === 'johnspassword') {
    req.session.user_id = johns_user_id_here;
  } else {
    res.send('Bad user/pass');

3) The logout route:

app.get('/logout', function (req, res) {
  delete req.session.user_id;

If you want to learn more about Express.js check their site here: If there's need for more complex stuff, checkout everyauth (it has a lot of auth methods available, for facebook, twitter etc; good tutorial on it here).

HTML5 LocalStorage: Checking if a key exists

This method worked for me:

if ("username" in localStorage) {
} else {

Generator expressions vs. list comprehensions

The important point is that the list comprehension creates a new list. The generator creates a an iterable object that will "filter" the source material on-the-fly as you consume the bits.

Imagine you have a 2TB log file called "hugefile.txt", and you want the content and length for all the lines that start with the word "ENTRY".

So you try starting out by writing a list comprehension:

logfile = open("hugefile.txt","r")
entry_lines = [(line,len(line)) for line in logfile if line.startswith("ENTRY")]

This slurps up the whole file, processes each line, and stores the matching lines in your array. This array could therefore contain up to 2TB of content. That's a lot of RAM, and probably not practical for your purposes.

So instead we can use a generator to apply a "filter" to our content. No data is actually read until we start iterating over the result.

logfile = open("hugefile.txt","r")
entry_lines = ((line,len(line)) for line in logfile if line.startswith("ENTRY"))

Not even a single line has been read from our file yet. In fact, say we want to filter our result even further:

long_entries = ((line,length) for (line,length) in entry_lines if length > 80)

Still nothing has been read, but we've specified now two generators that will act on our data as we wish.

Lets write out our filtered lines to another file:

outfile = open("filtered.txt","a")
for entry,length in long_entries:

Now we read the input file. As our for loop continues to request additional lines, the long_entries generator demands lines from the entry_lines generator, returning only those whose length is greater than 80 characters. And in turn, the entry_lines generator requests lines (filtered as indicated) from the logfile iterator, which in turn reads the file.

So instead of "pushing" data to your output function in the form of a fully-populated list, you're giving the output function a way to "pull" data only when its needed. This is in our case much more efficient, but not quite as flexible. Generators are one way, one pass; the data from the log file we've read gets immediately discarded, so we can't go back to a previous line. On the other hand, we don't have to worry about keeping data around once we're done with it.

How to store an output of shell script to a variable in Unix?

export a=$(

Hope this helps. Note there are no spaces between variable and =. To echo the output

echo $a

How to align an image dead center with bootstrap

I am using justify-content-center class to a row within a container. Works well with Bootstrap 4.

<div class="container-fluid">
  <div class="row justify-content-center">
   <img src="logo.png" />

VideoView Full screen in android application

I achieved it by switching to landscape orientation and setting layout params to MATCH_PARENT. Just before switching to fullscreen mode, we need to store current orientation mode and VideoView params indefaultScreenOrientationMode and defaultVideoViewParams variables correspondingly. So that we can use them when we exit from video fullscreen mode. Thus, when you want to open video in fullscreen mode, use makeVideoFullScreen() method, to exit - exitVideoFullScreen().

Please, note I used RelativeLayout for my VideoView, in your case it can be another layout type.

private RelativeLayout.LayoutParams defaultVideoViewParams;
private int defaultScreenOrientationMode;

// play video in fullscreen mode
private void makeVideoFullScreen() {

    defaultScreenOrientationMode = getResources().getConfiguration().orientation;
    defaultVideoViewParams = (LayoutParams) videoView.getLayoutParams();


    videoView.postDelayed(new Runnable() {

        public void run() {
            RelativeLayout.LayoutParams params = (RelativeLayout.LayoutParams) new RelativeLayout.LayoutParams(

            videoView.layout(10, 10, 10, 10);
    }, 700);

// close fullscreen mode
private void exitVideoFullScreen() {

    videoView.postDelayed(new Runnable() {

        public void run() {
            videoView.layout(10, 10, 10, 10);
    }, 700);

How do I prompt a user for confirmation in bash script?

Here's the function I use :

function ask_yes_or_no() {
    read -p "$1 ([y]es or [N]o): "
    case $(echo $REPLY | tr '[A-Z]' '[a-z]') in
        y|yes) echo "yes" ;;
        *)     echo "no" ;;

And an example using it:

if [[ "no" == $(ask_yes_or_no "Are you sure?") || \
      "no" == $(ask_yes_or_no "Are you *really* sure?") ]]
    echo "Skipped."
    exit 0

# Do something really dangerous...
  • The output is always "yes" or "no"
  • It's "no" by default
  • Everything except "y" or "yes" returns "no", so it's pretty safe for a dangerous bash script
  • And it's case insensitive, "Y", "Yes", or "YES" work as "yes".

I hope you like it,

jquery Ajax call - data parameters are not being passed to MVC Controller action

In my case, if I remove the the contentType, I get the Internal Server Error.

This is what I got working after multiple attempts:

var request =  $.ajax({
    type: 'POST',
    url: '/ControllerName/ActionName' ,
    contentType: 'application/json; charset=utf-8',
    data: JSON.stringify({ projId: 1, userId:1 }), //hard-coded value used for simplicity
    dataType: 'json'

request.done(function(msg) {
}); (jqXHR, textStatus, errorThrown) {
    alert("Request failed: " + jqXHR.responseStart +"-" + textStatus + "-" + errorThrown);

And this is the controller code:

public JsonResult ActionName(int projId, int userId)
    var obj = new ClassName();

    var result = obj.MethodName(projId, userId); // variable used for readability
    return Json(result, JsonRequestBehavior.AllowGet);

Please note, the case of ASP.NET is little different, we have to apply JSON.stringify() to the data as mentioned in the update of this answer.


Make sure, following jar file included in your class path and lib folder.


enter image description here

if you are using maven, make sure you have included dependency for spring-core-3xxxxx.jar file


Note : Replace ${org.springframework.version} with version number.

Read a variable in bash with a default value

You can use parameter expansion, e.g.

read -p "Enter your name [Richard]: " name
echo $name

Including the default value in the prompt between brackets is a fairly common convention

What does the :-Richard part do? From the bash manual:

${parameter:-word} If parameter is unset or null, the expansion of word is substituted. Otherwise, the value of parameter is substituted.

Also worth noting that...

In each of the cases below, word is subject to tilde expansion, parameter expansion, command substitution, and arithmetic expansion.

So if you use webpath=${webpath:-~/httpdocs} you will get a result of /home/user/expanded/path/httpdocs not ~/httpdocs, etc.

SASS :not selector

I tried re-creating this, and .someclass.notip was being generated for me but .someclass:not(.notip) was not, for as long as I did not have the @mixin tip() defined. Once I had that, it all worked.

$dropdown-width: 100px;
$comp-tip: true;

@mixin tip($pos:right) {


@mixin dropdown-pos($pos:right) {
  &:not(.notip) {
    @if $comp-tip == true{
      @if $pos == right {
        top:$dropdown-width * -0.6;
        background-color: #f00;
        @include tip($pos:$pos);
  &.notip {
    @if $pos == right {
      top: 0;
      left:$dropdown-width * 0.8;
      background-color: #00f;

.someclass { @include dropdown-pos(); }

EDIT: is a good place to debug your SASS because it gives you error messages. Undefined mixin 'tip'. it what I get when I remove @mixin tip($pos:right) { }

How to hide a View programmatically?

You can call view.setVisibility(View.GONE) if you want to remove it from the layout.

Or view.setVisibility(View.INVISIBLE) if you just want to hide it.

From Android Docs:


This view is invisible, but it still takes up space for layout purposes. Use with setVisibility(int) and android:visibility.


This view is invisible, and it doesn't take any space for layout purposes. Use with setVisibility(int) and android:visibility.

JPA With Hibernate Error: [PersistenceUnit: JPA] Unable to build EntityManagerFactory

Use above annotation if someone is facing :--org.hibernate.jpa.HibernatePersistenceProvider persistence provider when it attempted to create the container entity manager factory for the paymentenginePU persistence unit. The following error occurred: [PersistenceUnit: paymentenginePU] Unable to build Hibernate SessionFactory ** This is a solution if you are using Audit table.@Audit

Use:- @Audited(targetAuditMode = RelationTargetAuditMode.NOT_AUDITED) on superclass.

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

I had tried all the answers mentioned here. But it didn't work. I had to delete and create again. I am guessing it was due to new the "Authenticated Referral". If you have added Open Graph objects which are not approved, it might give you an error.

How to import functions from different js file in a Vue+webpack+vue-loader project

I was trying to organize my vue app code, and came across this question , since I have a lot of logic in my component and can not use other sub-coponents , it makes sense to use many functions in a separate js file and call them in the vue file, so here is my attempt

1)The Component (.vue file)

//MyComponent.vue file
  <div>Hello {{name}}</div>
  <button @click="function_A">Read Name</button>
  <button @click="function_B">Write Name</button>
  <button @click="function_C">Reset</button>

import Mylib from "./Mylib"; // <-- import
export default {
  name: "MyComponent",
  data() {
    return {
      name: "Bob",
      message: "click on the buttons"
  methods: {
    function_A() {
      Mylib.myfuncA(this); // <---read data
    function_B() {
      Mylib.myfuncB(this); // <---write data
    function_C() {
      Mylib.myfuncC(this); // <---write data

2)The External js file

let exports = {};

// this (vue instance) is passed as that , so we
// can read and write data from and to it as we please :)
exports.myfuncA = (that) => {
  that.message =
  "you hit ''myfuncA'' function that is located in Mylib.js  and = " +;

exports.myfuncB = (that) => {
  that.message =
  "you hit ''myfuncB'' function that is located in Mylib.js and now I will change the name to Nassim"; = "Nassim"; // <-- change name to Nassim

exports.myfuncC = (that) => {
  that.message =
  "you hit ''myfuncC'' function that is located in Mylib.js and now I will change the name back to Bob"; = "Bob"; // <-- change name to Bob

export default exports;

enter image description here 3)see it in action :


after getting more experience with Vue , I found out that you could use mixins too to split your code into different files and make it easier to code and maintain see

What is the difference between an Instance and an Object?

When a variable is declared of a custom type (class), only a reference is created, which is called an object. At this stage, no memory is allocated to this object. It acts just as a pointer (to the location where the object will be stored in future). This process is called 'Declaration'.

Employee e; // e is an object

On the other hand, when a variable of custom type is declared using the new operator, which allocates memory in heap to this object and returns the reference to the allocated memory. This object which is now termed as instance. This process is called 'Instantiation'.

Employee e = new Employee(); // e is an instance

On the other hand, in some languages such as Java, an object is equivalent to an instance, as evident from the line written in Oracle's documentation on Java:

Note: The phrase "instantiating a class" means the same thing as "creating an object." When you create an object, you are creating an "instance" of a class, therefore "instantiating" a class.

Change language of Visual Studio 2017 RC

You need reinstall VS.

Language Pack Support in Visual Studio 2017 RC


This release of Visual Studio supports only a single language pack for the user interface. You cannot install two languages for the user interface in the same instance of Visual Studio. In addition, you must select the language of Visual Studio during the initial install, and cannot change it during Modify.


These are known issues that will be fixed in an upcoming release. To change the language in this release, you can uninstall and reinstall Visual Studio.


How to import the class within the same directory or sub directory?

If and are not including classes then

from .user import User
from .dir import Dir

is not working. You should then import as

from . import user
from . import dir

Add one year in current date PYTHON

Look at this:


import datetime

def addYears(date, years):
    result = date + datetime.timedelta(366 * years)
    if years > 0:
        while result.year - date.year > years or date.month < result.month or <
            result += datetime.timedelta(-1)
    elif years < 0:
        while result.year - date.year < years or date.month > result.month or >
            result += datetime.timedelta(1)
    print "input: %s output: %s" % (date, result)
    return result

Example usage:

addYears(,1,1), -1)
addYears(,1,1), 0)
addYears(,1,1), 1)
addYears(,1,1), -10)
addYears(,1,1), 0)
addYears(,1,1), 10)

And output of this example:

input: 2012-01-01 output: 2011-01-01
input: 2012-01-01 output: 2012-01-01
input: 2012-01-01 output: 2013-01-01
input: 2012-01-01 output: 2002-01-01
input: 2012-01-01 output: 2012-01-01
input: 2012-01-01 output: 2022-01-01

Purpose of "%matplotlib inline"

If you don't know what backend is , you can read this:

Some people use matplotlib interactively from the python shell and have plotting windows pop up when they type commands. Some people run Jupyter notebooks and draw inline plots for quick data analysis. Others embed matplotlib into graphical user interfaces like wxpython or pygtk to build rich applications. Some people use matplotlib in batch scripts to generate postscript images from numerical simulations, and still others run web application servers to dynamically serve up graphs. To support all of these use cases, matplotlib can target different outputs, and each of these capabilities is called a backend; the "frontend" is the user facing code, i.e., the plotting code, whereas the "backend" does all the hard work behind-the-scenes to make the figure.

So when you type %matplotlib inline , it activates the inline backend. As discussed in the previous posts :

With this backend, the output of plotting commands is displayed inline within frontends like the Jupyter notebook, directly below the code cell that produced it. The resulting plots will then also be stored in the notebook document.

restrict edittext to single line

As android:singleLine="true" is now Depreciated so use


Use maxLines instead to change the layout of a static text, and use the textMultiLine flag in the inputType attribute instead for editable text views (if both singleLine and inputType are supplied, the inputType flags will override the value of singleLine).

sendUserActionEvent() is null

This has to do with having two buttons with the same ID in two different Activities, sometimes Android Studio can't find, You just have to give your button a new ID and re Build the Project

Apply CSS rules to a nested class inside a div

Use Css Selector for this, or learn more about Css Selector just go here

#main_text > .title {
  /* Style goes here */

#main_text .title {
  /* Style goes here */

PowerShell: Format-Table without headers

The -HideTableHeaders parameter unfortunately still causes the empty lines to be printed (and table headers appearently are still considered for column width). The only way I know that could reliably work here would be to format the output yourself:

| % { '{0,10} {1,20} {2,20}' -f $_.Operation,$_.AttributeName,$_.AttributeValue }

Where should I put the file?

Actually, I've just experienced this problem in a stardard Java project structure as follows:


In Eclipse I need to add the res folder to build path, however, in Intellij, I need to mark the res folder as resouces as the linked screenshot shows: right click on the res folder and mark as resources.

How to upgrade rubygems

I wouldn't use the debian packages, have a look at RVM or Rbenv.

calling java methods in javascript code

Java is a server side language, whereas javascript is a client side language. Both cannot communicate. If you have setup some server side script using Java you could use AJAX on the client in order to send an asynchronous request to it and thus invoke any possible Java functions. For example if you use jQuery as js framework you may take a look at the $.ajax() method. Or if you wanted to do it using plain javascript, here's a tutorial.

How can I get client information such as OS and browser

Update: The project is EOL and not maintained anymore. He recommends switching to the Browscap project.

You can use the bitwalker useragentutils library: It will provide you information about the Browser (name, type, version, manufacturer, etc.) and about the OperatingSystem. A good thing about it is that it is maintained. Access the link that I have provided to see the Maven dependency that you need to add to you project in order to use it.

See below sample code that returns the browser name and browser version.

    UserAgent userAgent = UserAgent.parseUserAgentString(request.getHeader("User-Agent"));
    Browser browser = userAgent.getBrowser();

    String browserName = browser.getName();
    // String browserName = browser.getGroup().getName();
    Version browserVersion = userAgent.getBrowserVersion();
    System.out.println("The user is using browser " + browserName + " - version " + browserVersion);

Passing parameters to a JDBC PreparedStatement

Do something like this, which also prevents SQL injection attacks

statement = con.prepareStatement("SELECT * from employee WHERE  userID = ?");
statement.setString(1, userID);
ResultSet rs = statement.executeQuery();

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

You're missing the () after ToString that marks it as a function call vs. a function reference (the kind you pass to delegates), which incidentally is why c# has no AddressOf operator, it's implied by how you type it.

Try this:

string guid = System.Guid.NewGuid().ToString();

Create JPA EntityManager without persistence.xml configuration file

DataNucleus JPA that I use also has a way of doing this in its docs. No need for Spring, or ugly implementation of PersistenceUnitInfo.

Simply do as follows

import org.datanucleus.metadata.PersistenceUnitMetaData;
import org.datanucleus.api.jpa.JPAEntityManagerFactory;

PersistenceUnitMetaData pumd = new PersistenceUnitMetaData("dynamic-unit", "RESOURCE_LOCAL", null);
pumd.addProperty("javax.persistence.jdbc.url", "jdbc:h2:mem:nucleus");
pumd.addProperty("javax.persistence.jdbc.user", "sa");
pumd.addProperty("javax.persistence.jdbc.password", "");
pumd.addProperty("datanucleus.schema.autoCreateAll", "true");

EntityManagerFactory emf = new JPAEntityManagerFactory(pumd, null);

Is there a way to instantiate a class by name in Java?

Use java reflection

Creating New Objects There is no equivalent to method invocation for constructors, because invoking a constructor is equivalent to creating a new object (to be the most precise, creating a new object involves both memory allocation and object construction). So the nearest equivalent to the previous example is to say:

import java.lang.reflect.*;

   public class constructor2 {
      public constructor2()

      public constructor2(int a, int b)
           "a = " + a + " b = " + b);

      public static void main(String args[])
         try {
           Class cls = Class.forName("constructor2");
           Class partypes[] = new Class[2];
            partypes[0] = Integer.TYPE;
            partypes[1] = Integer.TYPE;
            Constructor ct 
              = cls.getConstructor(partypes);
            Object arglist[] = new Object[2];
            arglist[0] = new Integer(37);
            arglist[1] = new Integer(47);
            Object retobj = ct.newInstance(arglist);
         catch (Throwable e) {

which finds a constructor that handles the specified parameter types and invokes it, to create a new instance of the object. The value of this approach is that it's purely dynamic, with constructor lookup and invocation at execution time, rather than at compilation time.

When should I use GC.SuppressFinalize()?

SupressFinalize tells the system that whatever work would have been done in the finalizer has already been done, so the finalizer doesn't need to be called. From the .NET docs:

Objects that implement the IDisposable interface can call this method from the IDisposable.Dispose method to prevent the garbage collector from calling Object.Finalize on an object that does not require it.

In general, most any Dispose() method should be able to call GC.SupressFinalize(), because it should clean up everything that would be cleaned up in the finalizer.

SupressFinalize is just something that provides an optimization that allows the system to not bother queuing the object to the finalizer thread. A properly written Dispose()/finalizer should work properly with or without a call to GC.SupressFinalize().

Most pythonic way to delete a file which may not exist

This is another solution:

if os.path.isfile(os.path.join(path, filename)):
    os.remove(os.path.join(path, filename))

How does the data-toggle attribute work? (What's its API?)

The data-* attributes is used to store custom data private to the page or application

So Bootstrap uses these attributes for saving states of objects

W3School data-* description

How to read attribute value from XmlNode in C#?

If you use chldNode as XmlElement instead of XmlNode, you can use

var attributeValue = chldNode.GetAttribute("Name");

The return value will just be an empty string, in case the attribute name does not exist.

So your loop could look like this:

XmlDocument document = new XmlDocument();
var nodes = document.SelectNodes("//Node/N0de/node");

foreach (XmlElement node in nodes)
    var attributeValue = node.GetAttribute("Name");

This will select all nodes <node> surrounded by <Node><N0de></N0de><Node> tags and subsequently loop through them and read the attribute "Name".

Swift: declare an empty dictionary

You have to give the dictionary a type

// empty dict with Ints as keys and Strings as values
var namesOfIntegers = Dictionary<Int, String>()

If the compiler can infer the type, you can use the shorter syntax

namesOfIntegers[16] = "sixteen"
// namesOfIntegers now contains 1 key-value pair
namesOfIntegers = [:]
// namesOfIntegers is once again an empty dictionary of type Int, String

What is the equivalent of Java's System.out.println() in Javascript?

I found a solution:

print("My message here");

Set timeout for ajax (jQuery)

Here's some examples that demonstrate setting and detecting timeouts in jQuery's old and new paradigmes.

Live Demo

Promise with jQuery 1.8+

    url: '/getData',
    timeout:3000 //3 second timeout
  //do something
}).catch(function(e) {
  if(e.statusText == 'timeout')
    alert('Native Promise: Failed from timeout'); 
    //do something. Try again perhaps?

jQuery 1.8+

    url: '/getData',
    timeout:3000 //3 second timeout
    //do something
}).fail(function(jqXHR, textStatus){
    if(textStatus === 'timeout')
        alert('Failed from timeout'); 
        //do something. Try again perhaps?

jQuery <= 1.7.2

    url: '/getData',
    error: function(jqXHR, textStatus){
        if(textStatus === 'timeout')
             alert('Failed from timeout');         
            //do something. Try again perhaps?
    success: function(){
        //do something
    timeout:3000 //3 second timeout

Notice that the textStatus param (or jqXHR.statusText) will let you know what the error was. This may be useful if you want to know that the failure was caused by a timeout.

error(jqXHR, textStatus, errorThrown)

A function to be called if the request fails. The function receives three arguments: The jqXHR (in jQuery 1.4.x, XMLHttpRequest) object, a string describing the type of error that occurred and an optional exception object, if one occurred. Possible values for the second argument (besides null) are "timeout", "error", "abort", and "parsererror". When an HTTP error occurs, errorThrown receives the textual portion of the HTTP status, such as "Not Found" or "Internal Server Error." As of jQuery 1.5, the error setting can accept an array of functions. Each function will be called in turn. Note: This handler is not called for cross-domain script and JSONP requests.


How to Set focus to first text input in a bootstrap modal after shown

Use the autofocus to search for the right form element:

$('.modal').on('', function() {

Python - add PYTHONPATH during command line module run

You may try this to execute a function inside your script

python -c "import sys; sys.path.append('/your/script/path'); import yourscript; yourscript.yourfunction()"

Getting vertical gridlines to appear in line plot in matplotlib

maybe this can solve the problem: matplotlib, define size of a grid on a plot

ax.grid(True, which='both')

The truth is that the grid is working, but there's only one v-grid in 00:00 and no grid in others. I meet the same problem that there's only one grid in Nov 1 among many days.

How can I check if a MySQL table exists with PHP?

Or you could use

show tables where Tables_in_{insert_db_name}='tablename';

DataGridView checkbox column - value and functionality

if u make this column in sql database (bit) as a data type u should edit this code

DataGridViewCheckBoxColumn doWork = new DataGridViewCheckBoxColumn();
doWork.HeaderText = "Include Dog";
doWork.FalseValue = "0";
doWork.TrueValue = "1";
dataGridView1.Columns.Insert(0, doWork);

with this

DataGridViewCheckBoxColumn doWork = new DataGridViewCheckBoxColumn();
doWork.HeaderText = "Include Dog";
doWork.FalseValue = "False";
doWork.TrueValue = "True";
dataGridView1.Columns.Insert(0, doWork);

How to split a dos path into its components in Python

Adapted the solution of @Mike Robins avoiding empty path elements at the beginning:

def parts(path):
    p,f = os.path.split(os.path.normpath(path))
    return parts(p) + [f] if f and p else [p] if p else []

os.path.normpath() is actually required only once and could be done in a separate entry function to the recursion.

Trying to get Laravel 5 email to work

If you ever have the same trouble and try everything online and it doesn't work, it is probably the config cache file that is sending the wrong information. You can find it in bootstrap/cache/config.php. Make sure the credentials are right in there. It took me a week to figure that out. I hope this will help someone someday.

Sublime Text 2 - Show file navigation in sidebar

Use Ctrl+0 to change focus to the sidebar.

Is the Scala 2.8 collections library a case of "the longest suicide note in history"?

Is this going to put people off coming to Scala?

I don't think it is the main factor that will affect how popular Scala will become, because Scala has a lot of power and its syntax is not as foreign to a Java/C++/PHP programmer as Haskell, OCaml, SML, Lisps, etc..

But I do think Scala's popularity will plateau at less than where Java is today, because I also think the next mainstream language must be much simplified, and the only way I see to get there is pure immutability, i.e. declarative like HTML, but Turing complete. However, I am biased because I am developing such a language, but I only did so after ruling out over a several month study that Scala could not suffice for what I needed.

Is this going to give Scala a bad name in the commercial world as an academic plaything that only dedicated PhD students can understand? Are CTOs and heads of software going to get scared off?

I don't think Scala's reputation will suffer from the Haskell complex. But I think that some will put off learning it, because for most programmers, I don't yet see a use case that forces them to use Scala, and they will procrastinate learning about it. Perhaps the highly-scalable server side is the most compelling use case.

And, for the mainstream market, first learning Scala is not a "breath of fresh air", where one is writing programs immediately, such as first using HTML or Python. Scala tends to grow on you, after one learns all the details that one stumbles on from the start. However, maybe if I had read Programming in Scala from the start, my experience and opinion of the learning curve would have been different.

Was the library re-design a sensible idea?


If you're using Scala commercially, are you worried about this? Are you planning to adopt 2.8 immediately or wait to see what happens?

I am using Scala as the initial platform of my new language. I probably wouldn't be building code on Scala's collection library if I was using Scala commercially otherwise. I would create my own category theory based library, since the one time I looked, I found Scalaz's type signatures even more verbose and unwieldy than Scala's collection library. Part of that problem perhaps is Scala's way of implementing type classes, and that is a minor reason I am creating my own language.

I decided to write this answer, because I wanted to force myself to research and compare Scala's collection class design to the one I am doing for my language. Might as well share my thought process.

The 2.8 Scala collections use of a builder abstraction is a sound design principle. I want to explore two design tradeoffs below.

  1. WRITE-ONLY CODE: After writing this section, I read Carl Smotricz's comment which agrees with what I expect to be the tradeoff. James Strachan and davetron5000's comments concur that the meaning of That (it is not even That[B]) and the mechanism of the implicit is not easy to grasp intuitively. See my use of monoid in issue #2 below, which I think is much more explicit. Derek Mahar's comment is about writing Scala, but what about reading the Scala of others that is not "in the common cases".

    One criticism I have read about Scala, is that it is easier to write it, than read the code that others have written. And I find this to be occasionally true for various reasons (e.g. many ways to write a function, automatic closures, Unit for DSLs, etc), but I am undecided if this is major factor. Here the use of implicit function parameters has pluses and minuses. On the plus side, it reduces verbosity and automates selection of the builder object. In Odersky's example the conversion from a BitSet, i.e. Set[Int], to a Set[String] is implicit. The unfamiliar reader of the code might not readily know what the type of collection is, unless they can reason well about the all the potential invisible implicit builder candidates which might exist in the current package scope. Of course, the experienced programmer and the writer of the code will know that BitSet is limited to Int, thus a map to String has to convert to a different collection type. But which collection type? It isn't specified explicitly.

  2. AD-HOC COLLECTION DESIGN: After writing this section, I read Tony Morris's comment and realized I am making nearly the same point. Perhaps my more verbose exposition will make the point more clear.

    In "Fighting Bit Rot with Types" Odersky & Moors, two use cases are presented. They are the restriction of BitSet to Int elements, and Map to pair tuple elements, and are provided as the reason that the general element mapping function, A => B, must be able to build alternative destination collection types. However, afaik this is flawed from a category theory perspective. To be consistent in category theory and thus avoid corner cases, these collection types are functors, in which each morphism, A => B, must map between objects in the same functor category, List[A] => List[B], BitSet[A] => BitSet[B]. For example, an Option is a functor that can be viewed as a collection of sets of one Some( object ) and the None. There is no general map from Option's None, or List's Nil, to other functors which don't have an "empty" state.

    There is a tradeoff design choice made here. In the design for collections library of my new language, I chose to make everything a functor, which means if I implement a BitSet, it needs to support all element types, by using a non-bit field internal representation when presented with a non-integer type parameter, and that functionality is already in the Set which it inherits from in Scala. And Map in my design needs to map only its values, and it can provide a separate non-functor method for mapping its (key,value) pair tuples. One advantage is that each functor is then usually also an applicative and perhaps a monad too. Thus all functions between element types, e.g. A => B => C => D => ..., are automatically lifted to the functions between lifted applicative types, e.g. List[A] => List[B] => List[C] => List[D] => .... For mapping from a functor to another collection class, I offer a map overload which takes a monoid, e.g. Nil, None, 0, "", Array(), etc.. So the builder abstraction function is the append method of a monoid and is supplied explicitly as a necessary input parameter, thus with no invisible implicit conversions. (Tangent: this input parameter also enables appending to non-empty monoids, which Scala's map design can't do.) Such conversions are a map and a fold in the same iteration pass. Also I provide a traversable, in the category sense, "Applicative programming with effects" McBride & Patterson, which also enables map + fold in a single iteration pass from any traversable to any applicative, where most every collection class is both. Also the state monad is an applicative and thus is a fully generalized builder abstraction from any traversable.

    So afaics the Scala collections is "ad-hoc" in the sense that it is not grounded in category theory, and category theory is the essense of higher-level denotational semantics. Although Scala's implicit builders are at first appearance "more generalized" than a functor model + monoid builder + traversable -> applicative, they are afaik not proven to be consistent with any category, and thus we don't know what rules they follow in the most general sense and what the corner cases will be given they may not obey any category model. It is simply not true that adding more variables makes something more general, and this was one of huge benefits of category theory is it provides rules by which to maintain generality while lifting to higher-level semantics. A collection is a category.

    I read somewhere, I think it was Odersky, as another justification for the library design, is that programming in a pure functional style has the cost of limited recursion and speed where tail recursion isn't used. I haven't found it difficult to employ tail recursion in every case that I have encountered so far.

Additionally I am carrying in my mind an incomplete idea that some of Scala's tradeoffs are due to trying to be both an mutable and immutable language, unlike for example Haskell or the language I am developing. This concurs with Tony Morris's comment about for comprehensions. In my language, there are no loops and no mutable constructs. My language will sit on top of Scala (for now) and owes much to it, and this wouldn't be possible if Scala didn't have the general type system and mutability. That might not be true though, because I think Odersky & Moors ("Fighting Bit Rot with Types") are incorrect to state that Scala is the only OOP language with higher-kinds, because I verified (myself and via Bob Harper) that Standard ML has them. Also appears SML's type system may be equivalently flexible (since 1980s), which may not be readily appreciated because the syntax is not so much similar to Java (and C++/PHP) as Scala. In any case, this isn't a criticism of Scala, but rather an attempt to present an incomplete analysis of tradeoffs, which is I hope germane to the question. Scala and SML don't suffer from Haskell's inability to do diamond multiple inheritance, which is critical and I understand is why so many functions in the Haskell Prelude are repeated for different types.

Adding blur effect to background in swift

You can make an extension of UIImageView.

Swift 2.0

import Foundation
import UIKit

extension UIImageView
    func makeBlurImage(targetImageView:UIImageView?)
        let blurEffect = UIBlurEffect(style: UIBlurEffectStyle.Dark)
        let blurEffectView = UIVisualEffectView(effect: blurEffect)
        blurEffectView.frame = targetImageView!.bounds

        blurEffectView.autoresizingMask = [.FlexibleWidth, .FlexibleHeight] // for supporting device rotation


override func viewDidLoad()

    let sampleImageView = UIImageView(frame: CGRectMake(0, 200, 300, 325))
    let sampleImage:UIImage = UIImage(named: "ic_120x120")!
    sampleImageView.image =  sampleImage

    //Convert To Blur Image Here


Swift 3 Extension

import Foundation
import UIKit

extension UIImageView
    func addBlurEffect()
        let blurEffect = UIBlurEffect(style: UIBlurEffectStyle.light)
        let blurEffectView = UIVisualEffectView(effect: blurEffect)
        blurEffectView.frame = self.bounds

        blurEffectView.autoresizingMask = [.flexibleWidth, .flexibleHeight] // for supporting device rotation




extension UIView {
  /// Remove UIBlurEffect from UIView
  func removeBlurEffect() {
    let blurredEffectViews = self.subviews.filter{$0 is UIVisualEffectView}
    blurredEffectViews.forEach{ blurView in

Swift 5.0:

import UIKit

extension UIImageView {
    func applyBlurEffect() {
        let blurEffect = UIBlurEffect(style: .light)
        let blurEffectView = UIVisualEffectView(effect: blurEffect)
        blurEffectView.frame = bounds
        blurEffectView.autoresizingMask = [.flexibleWidth, .flexibleHeight]

How to build a query string for a URL in C#?

Here's my late entry. I didn't like any of the others for various reasons, so I wrote my own.

This version features:

  • Use of StringBuilder only. No ToArray() calls or other extension methods. It doesn't look as pretty as some of the other responses, but I consider this a core function so efficiency is more important than having "fluent", "one-liner" code which hide inefficiencies.

  • Handles multiple values per key. (Didn't need it myself but just to silence Mauricio ;)

    public string ToQueryString(NameValueCollection nvc)
        StringBuilder sb = new StringBuilder("?");
        bool first = true;
        foreach (string key in nvc.AllKeys)
            foreach (string value in nvc.GetValues(key))
                if (!first)
                sb.AppendFormat("{0}={1}", Uri.EscapeDataString(key), Uri.EscapeDataString(value));
                first = false;
        return sb.ToString();

Example Usage

        var queryParams = new NameValueCollection()
            { "x", "1" },
            { "y", "2" },
            { "foo", "bar" },
            { "foo", "baz" },
            { "special chars", "? = &" },

        string url = "" + ToQueryString(queryParams);



Python TypeError must be str not int

Python comes with numerous ways of formatting strings:

New style .format(), which supports a rich formatting mini-language:

>>> temperature = 10
>>> print("the furnace is now {} degrees!".format(temperature))
the furnace is now 10 degrees!

Old style % format specifier:

>>> print("the furnace is now %d degrees!" % temperature)
the furnace is now 10 degrees!

In Py 3.6 using the new f"" format strings:

>>> print(f"the furnace is now {temperature} degrees!")
the furnace is now 10 degrees!

Or using print()s default separator:

>>> print("the furnace is now", temperature, "degrees!")
the furnace is now 10 degrees!

And least effectively, construct a new string by casting it to a str() and concatenating:

>>> print("the furnace is now " + str(temperature) + " degrees!")
the furnace is now 10 degrees!

Or join()ing it:

>>> print(' '.join(["the furnace is now", str(temperature), "degrees!"]))
the furnace is now 10 degrees!

JAVA_HOME and PATH are set but java -version still shows the old one

$JAVA_HOME/bin/java -version says 'Permission Denied'

If you cannot access or run code, it which be ignored if added to your path. You need to make it accessible and runnable or get a copy of your own.

Do an

ls -ld $JAVA_HOME $JAVA_HOME/bin $JAVA_HOME/bin/java

to see why you cannot access or run this program,.

Android Studio - debug keystore

You can specify your own debug keystore if you wish. This solution also gives you the ability to store your keys outside of the project directory as well as enjoy automation in the signing process. Yes you can go to File -> Project Structure and assign signing keystores and passwords in the Signing tab but that will put plaintext entries into your file which means your secrets might be disclosed (especially in repository commits). With this solution you get the control of using your own keystore and the magic of automation during debug and release builds.

1) Create a (if you don't already have one).

The location for this file depends on your OS:

   /home/<username>/.gradle/ (Linux)
   /Users/<username>/.gradle/ (Mac)
   C:\Users\<username>\.gradle (Windows)

2) Add an entry pointing to file. (example for Windows)\\Users\\<username>\\signing\\

3) Create file in the location you specified in Step 2 with the following information:


4) Modify your file to point to file to use the variables.

        && new File("")).exists()) {

    Properties props = new Properties()
    props.load(new FileInputStream(file(""))))

    android {
        signingConfigs {
            release {
                keyAlias 'release'
                keyPassword props['keystore.password']
                storeFile file(props['keystore'])
                storePassword props['keystore.password']
            debug {
                keyAlias 'debug'
                keyPassword props['keystore.password']
                storeFile file(props['keystore'])
                storePassword props['keystore.password']
        compileSdkVersion 19
        buildToolsVersion "20.0.0"
        defaultConfig {
            applicationId ""
            minSdkVersion 16
            targetSdkVersion 17
        buildTypes {
            release {


dependencies {

5) Enjoy! Now all of your keys will be outside of the root of the directory and yet you still have the joys of automation for each build.

If you get an error in your file about the "props" variable it's because you are not executing the "android {}" block inside the very first if condition where the props variable gets assigned so just move the entire android{ ... } section into the condition in which the props variable is assigned then try again.

I pieced these steps together from the information found here and here.

Pass Javascript Array -> PHP

So use the client-side loop to build a two-dimensional array of your arrays, and send the entire thing to PHP in one request.

Server-side, you'll need to have another loop which does its regular insert/update for each sub-array.

Inline JavaScript onclick function

Based on the answer that @Mukund Kumar gave here's a version that passes the event argument to the anonymous function:

<a href="#" onClick="(function(e){
    alert('Hey i am calling');
    return false;
})(arguments[0]);return false;">click here</a>

Access denied for root user in MySQL command-line

I had the same issue, and it turned out to be that MariaDB was set to allow only root to log in locally via the unix_socket plug-in, so clearing that setting allowed successfully logging in with the user specified on the command line, provided a correct password is entered, of course. See this answer on Ask Ubuntu

Carriage Return\Line feed in Java

The method newLine() ensures a platform-compatible new line is added (0Dh 0Ah for DOS, 0Dh for older Macs, 0Ah for Unix/Linux). Java has no way of knowing on which platform you are going to send the text. This conversion should be taken care of by the mail sending entities.

Select first and last row from grouped data

using which.min and which.max :

library(dplyr, warn.conflicts = F)
df %>% 
  group_by(id) %>% 
  slice(c(which.min(stopSequence), which.max(stopSequence)))

#> # A tibble: 6 x 3
#> # Groups:   id [3]
#>      id stopId stopSequence
#>   <dbl> <fct>         <dbl>
#> 1     1 a                 1
#> 2     1 c                 3
#> 3     2 b                 1
#> 4     2 c                 4
#> 5     3 b                 1
#> 6     3 a                 3


It is also much faster than the current accepted answer because we find the min and max value by group, instead of sorting the whole stopSequence column.

# create a 100k times longer data frame
df2 <- bind_rows(replicate(1e5, df, F)) 
  mm =df2 %>% 
    group_by(id) %>% 
    slice(c(which.min(stopSequence), which.max(stopSequence))),
  jeremy = df2 %>%
    group_by(id) %>%
    arrange(stopSequence) %>%
    filter(row_number()==1 | row_number()==n()))
#> Warning: Some expressions had a GC in every iteration; so filtering is disabled.
#> # A tibble: 2 x 6
#>   expression      min   median `itr/sec` mem_alloc `gc/sec`
#>   <bch:expr> <bch:tm> <bch:tm>     <dbl> <bch:byt>    <dbl>
#> 1 mm           22.6ms     27ms     34.9     14.2MB     21.3
#> 2 jeremy      254.3ms    273ms      3.66    58.4MB     11.0

Add SUM of values of two LISTS into new LIST

Try the following code:

first = [1, 2, 3, 4]
second = [2, 3, 4, 5]
third = map(sum, zip(first, second))

XAMPP: Couldn't start Apache (Windows 10)

Solving this problem is easy:

  1. Open a command prompt with administrator privileges
    • Find "cmd", right-click on it, then select "Administrator".
  2. In the prompt, type net stop W3SVC and Enter.

You can now click in WAMPP and restart all services. Open your browser and navigate to "localhost".

If you need to start W3SVC again,

  1. Open a command prompt with administrator privileges
  2. In the prompt, type net start W3SVC and Enter.

Hibernate - A collection with cascade=”all-delete-orphan” was no longer referenced by the owning entity instance

Following solution worked for me

//Parent class
@OneToMany(mappedBy = 'parent', 
           cascade= CascadeType.ALL, orphanRemoval = true)
@OrderBy(value="ordinal ASC")
List<Child> children = new ArrayList<>()

//Updated setter of children 
public void setChildren(List<Children> children) {
    for (Children child: children)

//Child class
private Parent parent;

How do I get LaTeX to hyphenate a word that contains a dash?

multi\hskip0pt-\hskip0pt disciplinary

You can e.g. define like


and then write


Note that the babel Russian language package has its own set of dashes that do not prohibit hyphenation, "~ (double quotation+tilde) for example.

c++ integer->std::string conversion. Simple function?

Not really, in the standard. Some implementations have a nonstandard itoa() function, and you could look up Boost's lexical_cast, but if you stick to the standard it's pretty much a choice between stringstream and sprintf() (snprintf() if you've got it).

What's is the difference between train, validation and test set, in neural networks?

Training set: A set of examples used for learning, that is to fit the parameters [i.e., weights] of the classifier.

Validation set: A set of examples used to tune the parameters [i.e., architecture, not weights] of a classifier, for example to choose the number of hidden units in a neural network.

Test set: A set of examples used only to assess the performance [generalization] of a fully specified classifier.

From section "What are the population, sample, training set, design set, validation"

The error surface will be different for different sets of data from your data set (batch learning). Therefore if you find a very good local minima for your test set data, that may not be a very good point, and may be a very bad point in the surface generated by some other set of data for the same problem. Therefore you need to compute such a model which not only finds a good weight configuration for the training set but also should be able to predict new data (which is not in the training set) with good error. In other words the network should be able to generalize the examples so that it learns the data and does not simply remembers or loads the training set by overfitting the training data.

The validation data set is a set of data for the function you want to learn, which you are not directly using to train the network. You are training the network with a set of data which you call the training data set. If you are using gradient based algorithm to train the network then the error surface and the gradient at some point will completely depend on the training data set thus the training data set is being directly used to adjust the weights. To make sure you don't overfit the network you need to input the validation dataset to the network and check if the error is within some range. Because the validation set is not being using directly to adjust the weights of the netowork, therefore a good error for the validation and also the test set indicates that the network predicts well for the train set examples, also it is expected to perform well when new example are presented to the network which was not used in the training process.

Early stopping is a way to stop training. There are different variations available, the main outline is, both the train and the validation set errors are monitored, the train error decreases at each iteration (backprop and brothers) and at first the validation error decreases. The training is stopped at the moment the validation error starts to rise. The weight configuration at this point indicates a model, which predicts the training data well, as well as the data which is not seen by the network . But because the validation data actually affects the weight configuration indirectly to select the weight configuration. This is where the Test set comes in. This set of data is never used in the training process. Once a model is selected based on the validation set, the test set data is applied on the network model and the error for this set is found. This error is a representative of the error which we can expect from absolutely new data for the same problem.


Also, in the case you do not have enough data for a validation set, you can use crossvalidation to tune the parameters as well as estimate the test error.

Sorting objects by property values

With ES6 arrow functions it will be like this:

//Let's say we have these cars
let cars = [ { brand: 'Porsche', top_speed: 260 },
  { brand: 'Benz', top_speed: 110 },
  { brand: 'Fiat', top_speed: 90 },
  { brand: 'Aston Martin', top_speed: 70 } ]

Array.prototype.sort() can accept a comparator function (here I used arrow notation, but ordinary functions work the same):

let sortedByBrand = [].sort((first, second) => first.brand > second.brand)

// [ { brand: 'Aston Martin', top_speed: 70 },
//   { brand: 'Benz', top_speed: 110 },
//   { brand: 'Fiat', top_speed: 90 },
//   { brand: 'Porsche', top_speed: 260 } ]

The above approach copies the contents of cars array into a new one and sorts it alphabetically based on brand names. Similarly, you can pass a different function:

let sortedBySpeed =[].sort((first, second) => first.top_speed > second.top_speed)

//[ { brand: 'Aston Martin', top_speed: 70 },
//  { brand: 'Fiat', top_speed: 90 },
//  { brand: 'Benz', top_speed: 110 },
//  { brand: 'Porsche', top_speed: 260 } ]

If you don't mind mutating the orginal array cars.sort(comparatorFunction) will do the trick.

Lazy Loading vs Eager Loading

It is better to use eager loading when it is possible, because it optimizes the performance of your application.


Eager loading

var customers= _context.customers.Include(c=> c.membershipType).Tolist();

lazy loading

In model customer has to define

Public virtual string membershipType {get; set;}

So when querying lazy loading is much slower loading all the reference objects, but eager loading query and select only the object which are relevant.

How do I create a WPF Rounded Corner container?

VB.Net code based implementation of kobusb's Border control solution. I used it to populate a ListBox of Button controls. The Button controls are created from MEF extensions. Each extension uses MEF's ExportMetaData attribute for a Description of the extension. The extensions are VisiFire charting objects. The user pushes a button, selected from the list of buttons, to execute the desired chart.

        ' Create a ListBox of Buttons, one button for each MEF charting component. 
    For Each c As Lazy(Of ICharts, IDictionary(Of String, Object)) In ext.ChartDescriptions
        Dim brdr As New Border
        brdr.BorderBrush = Brushes.Black
        brdr.BorderThickness = New Thickness(2, 2, 2, 2)
        brdr.CornerRadius = New CornerRadius(8, 8, 8, 8)
        Dim btn As New Button
        AddHandler btn.Click, AddressOf GenericButtonClick
        brdr.Child = btn
        brdr.Background = btn.Background
        btn.Margin = brdr.BorderThickness
        btn.Width = ChartsLBx.ActualWidth - 22
        btn.BorderThickness = New Thickness(0, 0, 0, 0)
        btn.Height = 22
        btn.Content = c.Metadata("Description")
        btn.Tag = c
        btn.ToolTip = "Push button to see " & c.Metadata("Description").ToString & " chart"
        Dim lbi As New ListBoxItem
        lbi.Content = brdr

Public Event Click As RoutedEventHandler

Private Sub GenericButtonClick(sender As Object, e As RoutedEventArgs)
    Dim btn As Button = DirectCast(sender, Button)
    Dim c As Lazy(Of ICharts, IDictionary(Of String, Object)) = DirectCast(btn.Tag, Lazy(Of ICharts, IDictionary(Of String, Object)))
    Dim w As Window = DirectCast(c.Value, Window)
    Dim cc As ICharts = DirectCast(c.Value, ICharts)
End Sub

<System.ComponentModel.Composition.Export(GetType(ICharts))> _
<System.ComponentModel.Composition.ExportMetadata("Description", "Data vs. Time")> _
Public Class DataTimeChart
    Implements ICharts

    Public Sub CreateChart() Implements ICharts.CreateChart
    End Sub
End Class

Public Interface ICharts
    Sub CreateChart()
End Interface

Public Class Extensibility
    Public Sub New()
        Dim catalog As New AggregateCatalog()

        catalog.Catalogs.Add(New AssemblyCatalog(GetType(Extensibility).Assembly))

        'Create the CompositionContainer with the parts in the catalog
        ChartContainer = New CompositionContainer(catalog)

        Catch ex As Exception
        End Try
    End Sub

    ' must use Lazy otherwise instantiation of Window will hold open app. Otherwise must specify Shutdown Mode of "Shutdown on Main Window".
    <ImportMany()> _
    Public Property ChartDescriptions As IEnumerable(Of Lazy(Of ICharts, IDictionary(Of String, Object)))

End Class

Setting std=c99 flag in GCC

How about alias gcc99= gcc -std=c99?

Styling a input type=number

UPDATE 17/03/2017

Original solution won't work anymore. The spinners are part of shadow dom. For now just to hide in chrome use:

input[type=number]::-webkit-inner-spin-button {_x000D_
  -webkit-appearance: none;_x000D_
<input type="number" />

or to always show:

input[type=number]::-webkit-inner-spin-button {_x000D_
  opacity: 1;_x000D_
<input type="number" />

You can try the following but keep in mind that works only for Chrome:

input[type=number]::-webkit-inner-spin-button { _x000D_
    -webkit-appearance: none;_x000D_
    color: #333;_x000D_
input[type=number]::-webkit-inner-spin-button:after {_x000D_
    content: "^";_x000D_
    right: 0;_x000D_
input[type=number]::-webkit-inner-spin-button:before {_x000D_
input[type=number]::-webkit-inner-spin-button:after {_x000D_
    -webkit-transform: rotate(180deg);_x000D_
<input type="number" />

Getting View's coordinates relative to the root layout

No need to calculate it manually.

Just use getGlobalVisibleRect like so:

Rect myViewRect = new Rect();
float x = myViewRect.left;
float y =;

Also note that for the centre coordinates, rather than something like:

float two = (float) 2
float cx = myViewRect.left + myView.getWidth() / two;
float cy = + myView.getHeight() / two;

You can just do:

float cx = myViewRect.exactCenterX();
float cy = myViewRect.exactCenterY();

Add a user control to a wpf window

You probably need to add the namespace:

<Window x:Class="UserControlTest.Window1"
    Title="User Control Test" Height="300" Width="300">
    <local:UserControl1 />

Eclipse java debugging: source not found

Well, here's what worked for me. I tried every possible solution on StackOverflow that there was. I tried changing my source location in the debug menu, I installed the m2e Eclipse plugin, I changed from embedded Maven, and I installed the run-jetty-run and nothing worked. Now, I will caveat that I was not trying to view an external person's source code, I just wanted to see my OWN code, but every time I "stepped in" to my methods that I wrote that were in MY project, I got the "Source now found" error.

After finally asking an expert, my issue was that the first thing Eclipse was doing was calling a ClassLoader, which you can see from the debug stack. All I had to do was F6 (step over) and then it took me back to my original call and then F5 (step in). And there was my code. Sigh...such a simple fix but an hour wasted.

How can I get date and time formats based on Culture Info?

You can retrieve the format strings from the CultureInfo DateTimeFormat property, which is a DateTimeFormatInfo instance. This in turn has properties like ShortDatePattern and ShortTimePattern, containing the format strings:

CultureInfo us = new CultureInfo("en-US");
string shortUsDateFormatString = us.DateTimeFormat.ShortDatePattern;
string shortUsTimeFormatString = us.DateTimeFormat.ShortTimePattern;

CultureInfo uk = new CultureInfo("en-GB");
string shortUkDateFormatString = uk.DateTimeFormat.ShortDatePattern;
string shortUkTimeFormatString = uk.DateTimeFormat.ShortTimePattern;

If you simply want to format the date/time using the CultureInfo, pass it in as your IFormatter when converting the DateTime to a string, using the ToString method:

string us = myDate.ToString(new CultureInfo("en-US"));
string uk = myDate.ToString(new CultureInfo("en-GB"));

Why use sys.path.append(path) instead of sys.path.insert(1, path)?

If you really need to use sys.path.insert, consider leaving sys.path[0] as it is:

sys.path.insert(1, path_to_dev_pyworkbooks)

This could be important since 3rd party code may rely on sys.path documentation conformance:

As initialized upon program startup, the first item of this list, path[0], is the directory containing the script that was used to invoke the Python interpreter.

Get a worksheet name using Excel VBA

Sub FnGetSheetsName()

    Dim mainworkBook As Workbook

    Set mainworkBook = ActiveWorkbook

    For i = 1 To mainworkBook.Sheets.Count

    'Either we can put all names in an array , here we are printing all the names in Sheet 2

    mainworkBook.Sheets("Sheet2").Range("A" & i) = mainworkBook.Sheets(i).Name

    Next i

End Sub

What is a Data Transfer Object (DTO)?

A Data Transfer Object is an object that is used to encapsulate data, and send it from one subsystem of an application to another.

DTOs are most commonly used by the Services layer in an N-Tier application to transfer data between itself and the UI layer. The main benefit here is that it reduces the amount of data that needs to be sent across the wire in distributed applications. They also make great models in the MVC pattern.

Another use for DTOs can be to encapsulate parameters for method calls. This can be useful if a method takes more than 4 or 5 parameters.

When using the DTO pattern, you would also make use of DTO assemblers. The assemblers are used to create DTOs from Domain Objects, and vice versa.

The conversion from Domain Object to DTO and back again can be a costly process. If you're not creating a distributed application, you probably won't see any great benefits from the pattern, as Martin Fowler explains here

CMD: Export all the screen content to a text file

If you are looking for each command separately

To export all the output of the command prompt in text files. Simply follow the following syntax.

C:> [syntax] >file.txt

The above command will create result of syntax in file.txt. Where new file.txt will be created on the current folder that you are in.

For example,

C:Result> dir >file.txt

To copy the whole session, Try this:

Copy & Paste a command session as follows:

1.) At the end of your session, click the upper left corner to display the menu.
Then select.. Edit -> Select all

2.) Again, click the upper left corner to display the menu.
Then select.. Edit -> Copy

3.) Open your favorite text editor and use Ctrl+V or your normal
Paste operation to paste in the text.

find the array index of an object with a specific key value in underscore

If you're expecting multiple matches and hence need an array to be returned, try:

_.where(Users, {age: 24})

If the property value is unique and you need the index of the match, try:

_.findWhere(Users, {_id: 10})

How to use JavaScript to change the form action

I wanted to use JavaScript to change a form's action, so I could have different submit inputs within the same form linking to different pages.

I also had the added complication of using Apache rewrite to change into I found that changing the form's action caused (with no page parameter) to be rendered, even though the expected URL ( was displayed in the address bar.

To get around this, I used JavaScript to insert a hidden field to set the page parameter. I still changed the form's action, just so the address bar displayed the correct URL.

function setAction (element, page)
    /* Insert a hidden input into the form to set the page as a parameter.
    var input = document.createElement("input");

    /* Change the form's action. This doesn't chage which page is displayed,
     * it just make the URL look right.
    element.form.action = '/' + page;

In the form:

<input type="submit" onclick='setAction(this,"my-page")' value="Click Me!" />

Here are my Apache rewrite rules:

RewriteRule ^/(.*)$ %{DOCUMENT_ROOT}/$1&%{QUERY_STRING}

I'd be interested in any explanation as to why just setting the action didn't work.

What is output buffering?

Output Buffering for Web Developers, a Beginner’s Guide:

Without output buffering (the default), your HTML is sent to the browser in pieces as PHP processes through your script. With output buffering, your HTML is stored in a variable and sent to the browser as one piece at the end of your script.

Advantages of output buffering for Web developers

  • Turning on output buffering alone decreases the amount of time it takes to download and render our HTML because it's not being sent to the browser in pieces as PHP processes the HTML.
  • All the fancy stuff we can do with PHP strings, we can now do with our whole HTML page as one variable.
  • If you've ever encountered the message "Warning: Cannot modify header information - headers already sent by (output)" while setting cookies, you'll be happy to know that output buffering is your answer.

EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0) on dispatch_semaphore_dispose

My problem was took IBOutlet but didn't connect with interface builder and using in swift file.

How can I compare two lists in python and return matches

Quick way:


How can I avoid running ActiveRecord callbacks?

The only way to prevent all after_save callbacks is to have the first one return false.

Perhaps you could try something like (untested):

class MyModel < ActiveRecord::Base
  attr_accessor :skip_after_save

  def after_save
    return false if @skip_after_save
    ... blah blah ...


m = # ... etc etc
m.skip_after_save = true

Show div on scrollDown after 800px

If you want to show a div after scrolling a number of pixels:

Working Example

$(document).scroll(function() {
  var y = $(this).scrollTop();
  if (y > 800) {
  } else {

$(document).scroll(function() {
  var y = $(this).scrollTop();
  if (y > 800) {
  } else {
body {
  height: 1600px;
.bottomMenu {
  display: none;
  position: fixed;
  bottom: 0;
  width: 100%;
  height: 60px;
  border-top: 1px solid #000;
  background: red;
  z-index: 1;
<script src=""></script>
<p>Scroll down... </p>
<div class="bottomMenu"></div>

Its simple, but effective.

Documentation for .scroll()
Documentation for .scrollTop()

If you want to show a div after scrolling a number of pixels,

without jQuery:

Working Example

myID = document.getElementById("myID");

var myScrollFunc = function() {
  var y = window.scrollY;
  if (y >= 800) {
    myID.className = "bottomMenu show"
  } else {
    myID.className = "bottomMenu hide"

window.addEventListener("scroll", myScrollFunc);

myID = document.getElementById("myID");

var myScrollFunc = function() {
  var y = window.scrollY;
  if (y >= 800) {
    myID.className = "bottomMenu show"
  } else {
    myID.className = "bottomMenu hide"

window.addEventListener("scroll", myScrollFunc);
body {
  height: 2000px;
.bottomMenu {
  position: fixed;
  bottom: 0;
  width: 100%;
  height: 60px;
  border-top: 1px solid #000;
  background: red;
  z-index: 1;
  transition: all 1s;
.hide {
  opacity: 0;
  left: -100%;
.show {
  opacity: 1;
  left: 0;
<div id="myID" class="bottomMenu hide"></div>

Documentation for .scrollY
Documentation for .className
Documentation for .addEventListener

If you want to show an element after scrolling to it:

Working Example

$('h1').each(function () {
    var y = $(document).scrollTop();
    var t = $(this).parent().offset().top;
    if (y > t) {
    } else {

$(document).scroll(function() {
  //Show element after user scrolls 800px
  var y = $(this).scrollTop();
  if (y > 800) {
  } else {

  // Show element after user scrolls past 
  // the top edge of its parent 
  $('h1').each(function() {
    var t = $(this).parent().offset().top;
    if (y > t) {
    } else {
body {
  height: 1600px;
.bottomMenu {
  display: none;
  position: fixed;
  bottom: 0;
  width: 100%;
  height: 60px;
  border-top: 1px solid #000;
  background: red;
  z-index: 1;
.scrollPast {
  width: 100%;
  height: 150px;
  background: blue;
  position: relative;
  top: 50px;
  margin: 20px 0;
h1 {
  display: none;
  position: absolute;
  bottom: 0;
<script src=""></script>
<p>Scroll Down...</p>
<div class="scrollPast">
  <h1>I fade in when you scroll to my parent</h1>

<div class="scrollPast">
  <h1>I fade in when you scroll to my parent</h1>

<div class="scrollPast">
  <h1>I fade in when you scroll to my parent</h1>

<div class="bottomMenu">I fade in when you scroll past 800px</div>

Note that you can't get the offset of elements set to display: none;, grab the offset of the element's parent instead.

Documentation for .each()
Documentation for .parent()
Documentation for .offset()

If you want to have a nav or div stick or dock to the top of the page once you scroll to it and unstick/undock when you scroll back up:

Working Example

$(document).scroll(function () {
    //stick nav to top of page
    var y = $(this).scrollTop();
    var navWrap = $('#navWrap').offset().top;
    if (y > navWrap) {
    } else {

#navWrap {
nav {
    height: 70px;
.sticky {
    position: fixed;

$(document).scroll(function () {
    //stick nav to top of page
    var y = $(this).scrollTop();
    var navWrap = $('#navWrap').offset().top;
    if (y > navWrap) {
    } else {
body {
#navWrap {
nav {
    height: 70px;
.sticky {
    position: fixed;
h1 {
    margin: 0;
<script src=""></script>
<p>Zombie ipsum reversus ab viral inferno, nam rick grimes malum cerebro. De carne lumbering animata corpora quaeritis. Summus brains sit, morbo vel maleficia? De apocalypsi gorger omero undead survivor dictum mauris. Hi mindless mortuis soulless creaturas,
  imo evil stalking monstra adventus resi dentevil vultus comedat cerebella viventium. Qui animated corpse, cricket bat max brucks terribilem incessu zomby. The voodoo sacerdos flesh eater, suscitat mortuos comedere carnem virus. Zonbi tattered for solum
  oculi eorum defunctis go lum cerebro. Nescio brains an Undead zombies. Sicut malus putrid voodoo horror. Nigh tofth eliv ingdead.</p>
<div id="navWrap">
    <h1>I stick to the top when you scroll down and unstick when you scroll up to my original position</h1>

<p>Zombie ipsum reversus ab viral inferno, nam rick grimes malum cerebro. De carne lumbering animata corpora quaeritis. Summus brains sit, morbo vel maleficia? De apocalypsi gorger omero undead survivor dictum mauris. Hi mindless mortuis soulless creaturas,
  imo evil stalking monstra adventus resi dentevil vultus comedat cerebella viventium. Qui animated corpse, cricket bat max brucks terribilem incessu zomby. The voodoo sacerdos flesh eater, suscitat mortuos comedere carnem virus. Zonbi tattered for solum
  oculi eorum defunctis go lum cerebro. Nescio brains an Undead zombies. Sicut malus putrid voodoo horror. Nigh tofth eliv ingdead.</p>

Directly assigning values to C Pointers

First Program with comments

#include <stdio.h>

int main(){
    int *ptr;             //Create a pointer that points to random memory address

    *ptr = 20;            //Dereference that pointer, 
                          // and assign a value to random memory address.
                          //Depending on external (not inside your program) state
                          // this will either crash or SILENTLY CORRUPT another 
                          // data structure in your program.  

    printf("%d", *ptr);   //Print contents of same random memory address
                          // May or may not crash, depending on who owns this address

    return 0;             

Second Program with comments

#include <stdio.h>

int main(){
    int *ptr;              //Create pointer to random memory address

    int q = 50;            //Create local variable with contents int 50

    ptr = &q;              //Update address targeted by above created pointer to point
                           // to local variable your program properly created

    printf("%d", *ptr);    //Happily print the contents of said local variable (q)
    return 0;

The key is you cannot use a pointer until you know it is assigned to an address that you yourself have managed, either by pointing it at another variable you created or to the result of a malloc call.

Using it before is creating code that depends on uninitialized memory which will at best crash but at worst work sometimes, because the random memory address happens to be inside the memory space your program already owns. God help you if it overwrites a data structure you are using elsewhere in your program.

How to list the contents of a package using YUM?

rpm -ql [packageName]


# rpm -ql php-fpm


No need to install yum-utils, or to know the location of the rpm file.

What are the advantages and disadvantages of recursion?

I personally prefer using Iterative over recursive function. Especially if you function has complex/heavy logic and number of iterations are large. This because with every recursive call call stack increases. It could potentially crash the stack if you operations are too large and also slow up process.

What does "select count(1) from table_name" on any database tables mean?

Here is a link that will help answer your questions. In short:

count(*) is the correct way to write it and count(1) is OPTIMIZED TO BE count(*) internally -- since

a) count the rows where 1 is not null is less efficient than
b) count the rows

Python - Module Not Found

You need to make sure the module is installed for all versions of python

You can check to see if a module is installed for python by running:

pip uninstall moduleName

If it is installed, it will ask you if you want to delete it or not. My issue was that it was installed for python, but not for python3. To check to see if a module is installed for python3, run:

python3 -m pip uninstall moduleName

After doing this, if you find that a module is not installed for one or both versions, use these two commands to install the module.

  • pip install moduleName
  • python3 -m pip install moduleName

What does a (+) sign mean in an Oracle SQL WHERE clause?

This is an Oracle-specific notation for an outer join. It means that it will include all rows from t1, and use NULLS in the t0 columns if there is no corresponding row in t0.

In standard SQL one would write:


Oracle recommends not to use those joins anymore if your version supports ANSI joins (LEFT/RIGHT JOIN) :

Oracle recommends that you use the FROM clause OUTER JOIN syntax rather than the Oracle join operator. Outer join queries that use the Oracle join operator (+) are subject to the following rules and restrictions […]

php static function

Calling non-static methods statically generates an E_STRICT level warning.

Get distance between two points in canvas

i tend to use this calculation a lot in things i make, so i like to add it to the Math object:

  if(!x2) x2=0; 
  if(!y2) y2=0;
  return Math.sqrt((x2-x1)*(x2-x1)+(y2-y1)*(y2-y1)); 
Math.dist(0,0, 3,4); //the output will be 5
Math.dist(1,1, 4,5); //the output will be 5
Math.dist(3,4); //the output will be 5


this approach is especially happy making when you end up in situations something akin to this (i often do):

varName.dist=Math.sqrt( ( (varName.paramX-varX)/2-cx )*( (varName.paramX-varX)/2-cx ) + ( (varName.paramY-varY)/2-cy )*( (varName.paramY-varY)/2-cy ) );

that horrid thing becomes the much more manageable:

varName.dist=Math.dist((varName.paramX-varX)/2, (varName.paramY-varY)/2, cx, cy);

What does DIM stand for in Visual Basic and BASIC?

Dim originally (in BASIC) stood for Dimension, as it was used to define the dimensions of an array.

(The original implementation of BASIC was Dartmouth BASIC, which descended from FORTRAN, where DIMENSION is spelled out.)

Nowadays, Dim is used to define any variable, not just arrays, so its meaning is not intuitive anymore.

How can I check whether a option already exist in select by JQuery

Another way using jQuery:

var exists = false; 
$('#yourSelect  option').each(function(){
  if (this.value == yourValue) {
    exists = true;

Short rot13 function - Python

Try this:

import codecs
codecs.encode("text to be rot13()'ed", "rot_13")

Is there a C++ gdb GUI for Linux?

Check out Nemiver C/C++ Debugger. It is easy to install in Ubuntu (Developer Tools/Debugging).

Update: New link.

proper name for python * operator?

I say "star-args" and Python people seem to know what i mean.

** is trickier - I think just "qargs" since it is usually used as **kw or **kwargs

“Origin null is not allowed by Access-Control-Allow-Origin” error for request made by application running from a file:// URL

Make sure you are using the latest version of JQuery. We were facing this error for JQuery 1.10.2 and the error got resolved after using JQuery 1.11.1

Is there a PowerShell "string does not contain" cmdlet or syntax?

You can use the -notmatch operator to get the lines that don't have the characters you are interested in.

     Get-Content $FileName | foreach-object { 
     if ($_ -notmatch $arrayofStringsNotInterestedIn) { $) }

How to make a checkbox checked with jQuery?



Finding the handle to a WPF window

you can use :


Calling functions in a DLL from C++

Can also export functions from dll and import from the exe, it is more tricky at first but in the end is much easier than calling LoadLibrary/GetProcAddress. See MSDN.

When creating the project with the VS wizard there's a check box in the dll that let you export functions.

Then, in the exe application you only have to #include a header from the dll with the proper definitions, and add the dll project as a dependency to the exe application.

Check this other question if you want to investigate this point further Exporting functions from a DLL with dllexport.

Excluding Maven dependencies

Global exclusions look like they're being worked on, but until then...

From the Sonatype maven reference (bottom of the page):

Dependency management in a top-level POM is different from just defining a dependency on a widely shared parent POM. For starters, all dependencies are inherited. If mysql-connector-java were listed as a dependency of the top-level parent project, every single project in the hierarchy would have a reference to this dependency. Instead of adding in unnecessary dependencies, using dependencyManagement allows you to consolidate and centralize the management of dependency versions without adding dependencies which are inherited by all children. In other words, the dependencyManagement element is equivalent to an environment variable which allows you to declare a dependency anywhere below a project without specifying a version number.

As an example:


It doesn't make the code less verbose overall, but it does make it less verbose where it counts. If you still want it less verbose you can follow these tips also from the Sonatype reference.

How can I change the Y-axis figures into percentages in a barplot?

Borrowed from @Deena above, that function modification for labels is more versatile than you might have thought. For example, I had a ggplot where the denominator of counted variables was 140. I used her example thus:

scale_y_continuous(labels = function(x) paste0(round(x/140*100,1), "%"), breaks = seq(0, 140, 35))

This allowed me to get my percentages on the 140 denominator, and then break the scale at 25% increments rather than the weird numbers it defaulted to. The key here is that the scale breaks are still set by the original count, not by your percentages. Therefore the breaks must be from zero to the denominator value, with the third argument in "breaks" being the denominator divided by however many label breaks you want (e.g. 140 * 0.25 = 35).

How to call webmethod in C#

This is a bit late, but I just stumbled on this problem, trying to resolve my own problem of this kind. I then realized that I had this line in the ajax post wrong:

data: "{'quantity' : " + total_qty + ",'itemId':" + itemId + "}",

It should be:

data: "{quantity : '" + total_qty + "',itemId: '" + itemId + "'}",

As well as the WebMethod to:

public static string AddTo_Cart(string quantity, string itemId)

And this resolved my problem.

Hope it may be of help to someone else as well.

Android Use Done button on Keyboard to click button

You can use this one also (sets a special listener to be called when an action is performed on the EditText), it works both for DONE and RETURN:

max.setOnEditorActionListener(new OnEditorActionListener() {
        public boolean onEditorAction(TextView v, int actionId, KeyEvent event) {
            if ((event != null && (event.getKeyCode() == KeyEvent.KEYCODE_ENTER)) || (actionId == EditorInfo.IME_ACTION_DONE)) {
                Log.i(TAG,"Enter pressed");
            return false;

How do I group Windows Form radio buttons?

I like the concept of grouping RadioButtons in WPF. There is a property GroupName that specifies which RadioButton controls are mutually exclusive (

So I wrote a derived class for WinForms that supports this feature:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Diagnostics;
using System.Windows.Forms.VisualStyles;
using System.Drawing;
using System.ComponentModel;

namespace Use.your.own
    public class AdvancedRadioButton : CheckBox
        public enum Level { Parent, Form };

        Description("Gets or sets the level that specifies which RadioButton controls are affected."),
        public Level GroupNameLevel { get; set; }

        Description("Gets or sets the name that specifies which RadioButton controls are mutually exclusive.")]
        public string GroupName { get; set; }

        protected override void OnCheckedChanged(EventArgs e)

            if (Checked)
                var arbControls = (dynamic)null;
                switch (GroupNameLevel)
                    case Level.Parent:
                        if (this.Parent != null)
                            arbControls = GetAll(this.Parent, typeof(AdvancedRadioButton));
                    case Level.Form:
                        Form form = this.FindForm();
                        if (form != null)
                            arbControls = GetAll(this.FindForm(), typeof(AdvancedRadioButton));
                if (arbControls != null)
                    foreach (Control control in arbControls)
                        if (control != this &&
                            (control as AdvancedRadioButton).GroupName == this.GroupName)
                            (control as AdvancedRadioButton).Checked = false;

        protected override void OnClick(EventArgs e)
            if (!Checked)

        protected override void OnPaint(PaintEventArgs pevent)
            CheckBoxRenderer.DrawParentBackground(pevent.Graphics, pevent.ClipRectangle, this);

            RadioButtonState radioButtonState;
            if (Checked)
                radioButtonState = RadioButtonState.CheckedNormal;
                if (Focused)
                    radioButtonState = RadioButtonState.CheckedHot;
                if (!Enabled)
                    radioButtonState = RadioButtonState.CheckedDisabled;
                radioButtonState = RadioButtonState.UncheckedNormal;
                if (Focused)
                    radioButtonState = RadioButtonState.UncheckedHot;
                if (!Enabled)
                    radioButtonState = RadioButtonState.UncheckedDisabled;

            Size glyphSize = RadioButtonRenderer.GetGlyphSize(pevent.Graphics, radioButtonState);
            Rectangle rect = pevent.ClipRectangle;
            rect.Width -= glyphSize.Width;
            rect.Location = new Point(rect.Left + glyphSize.Width, rect.Top);

            RadioButtonRenderer.DrawRadioButton(pevent.Graphics, new System.Drawing.Point(0, rect.Height / 2 - glyphSize.Height / 2), rect, this.Text, this.Font, this.Focused, radioButtonState);

        private IEnumerable<Control> GetAll(Control control, Type type)
            var controls = control.Controls.Cast<Control>();

            return controls.SelectMany(ctrl => GetAll(ctrl, type))
                                      .Where(c => c.GetType() == type);

How do I clone a Django model instance object and save it to the database?

Just change the primary key of your object and run save().

obj = Foo.objects.get(pk=<some_existing_pk>) = None

If you want auto-generated key, set the new key to None.

More on UPDATE/INSERT here.

Official docs on copying model instances:

Converting HTML string into DOM elements?

Okay, I realized the answer myself, after I had to think about other people's answers. :P

var htmlContent = ... // a response via AJAX containing HTML
var e = document.createElement('div');
e.setAttribute('style', 'display: none;');
e.innerHTML = htmlContent;
var htmlConvertedIntoDom = e.lastChild.childNodes; // the HTML converted into a DOM element :), now let's remove the

Where is adb.exe in windows 10 located?

If you are not able to find platform-tools folder, please open SDK Manager and install "Android SDK Platform-Tools" from SDK Tools tab.

How to copy text to the client's clipboard using jQuery?

Copying to the clipboard is a tricky task to do in Javascript in terms of browser compatibility. The best way to do it is using a small flash. It will work on every browser. You can check it in this article.

Here's how to do it for Internet Explorer:

function copy (str)
    //for IE ONLY!

Adding data attribute to DOM

jQuery's .data() does a couple things but it doesn't add the data to the DOM as an attribute. When using it to grab a data attribute, the first thing it does is create a jQuery data object and sets the object's value to the data attribute. After that, it's essentially decoupled from the data attribute.


<div data-foo="bar"></div>

If you grabbed the value of the attribute using .data('foo'), it would return "bar" as you would expect. If you then change the attribute using .attr('data-foo', 'blah') and then later use .data('foo') to grab the value, it would return "bar" even though the DOM says data-foo="blah". If you use .data() to set the value, it'll change the value in the jQuery object but not in the DOM.

Basically, .data() is for setting or checking the jQuery object's data value. If you are checking it and it doesn't already have one, it creates the value based on the data attribute that is in the DOM. .attr() is for setting or checking the DOM element's attribute value and will not touch the jQuery data value. If you need them both to change you should use both .data() and .attr(). Otherwise, stick with one or the other.

Waiting for background processes to finish before exiting script

If you want to wait for jobs to finish, use wait. This will make the shell wait until all background jobs complete. However, if any of your jobs daemonize themselves, they are no longer children of the shell and wait will have no effect (as far as the shell is concerned, the child is already done. Indeed, when a process daemonizes itself, it does so by terminating and spawning a new process that inherits its role).

{ sleep 5; echo waking up after 5 seconds; } &
{ sleep 1; echo waking up after 1 second; } &
echo all jobs are done!

Redirect on select option in select box

This can be archived by adding code on the onchange event of the select control.

For Example:

<select onchange="this.options[this.selectedIndex].value && (window.location = this.options[this.selectedIndex].value);">
    <option value=""></option>
    <option value="">Google</option>
    <option value="">Gmail</option>
    <option value="">Youtube</option>

Execute PowerShell Script from C# with Commandline Arguments

Try creating scriptfile as a separate command:

Command myCommand = new Command(scriptfile);

then you can add parameters with

CommandParameter testParam = new CommandParameter("key","value");

and finally


Here is the complete, edited code:

RunspaceConfiguration runspaceConfiguration = RunspaceConfiguration.Create();

Runspace runspace = RunspaceFactory.CreateRunspace(runspaceConfiguration);

Pipeline pipeline = runspace.CreatePipeline();

//Here's how you add a new script with arguments
Command myCommand = new Command(scriptfile);
CommandParameter testParam = new CommandParameter("key","value");


// Execute PowerShell script
results = pipeline.Invoke();

HTML 5 Geo Location Prompt in Chrome

if you're hosting behind a server, and still facing issues: try changing localhost to e.g. http://localhost:8080/ to

The issue I was facing was that I was serving a site using apache tomcat within an eclipse IDE (eclipse luna).

For my sanity check I was using Remy Sharp's demo:

and was getting the error after making minor tweaks to the error function despite hosting the code on the server (was only working on firefox and failing on chrome and safari):

"User denied Geolocation"

I made the following change to get more detailed error message:

function error(msg) {
  var s = document.querySelector('#status');
  msg = msg.message ? msg.message : msg; //add this line
  s.innerHTML = typeof msg == 'string' ? msg : "failed";
  s.className = 'fail';

  // console.log(arguments);

failing on internet explorer behind virtualbox IE10 on :

"The current location cannot be determined"

compare differences between two tables in mysql

I found another solution in this link

SELECT MIN (tbl_name) AS tbl_name, PK, column_list
  SELECT ' source_table ' as tbl_name, S.PK, S.column_list
  FROM source_table AS S
  SELECT 'destination_table' as tbl_name, D.PK, D.column_list
  FROM destination_table AS D 
)  AS alias_table
GROUP BY PK, column_list

How to implement authenticated routes in React Router 4?

const Root = ({ session }) => {
  const isLoggedIn = session && session.getCurrentUser
  return (
      {!isLoggedIn ? (
          <Route path="/signin" component={<Signin />} />
          <Redirect to="/signin" />
      ) : (
          <Route path="/" exact component={Home} />
          <Route path="/about" component={About} />
          <Route path="/something-else" component={SomethingElse} />
          <Redirect to="/" />

Page Redirect after X seconds wait using JavaScript

setTimeout('Redirect()', 1000);
function Redirect() 

//document.write("You will be Redirect to a new page in 1000 -> 1 Seconds, 2000 -> 2 Seconds");

Implementing INotifyPropertyChanged - does a better way exist?

I created an Extension Method in my base Library for reuse:

public static class INotifyPropertyChangedExtensions
    public static bool SetPropertyAndNotify<T>(this INotifyPropertyChanged sender,
               PropertyChangedEventHandler handler, ref T field, T value, 
               [CallerMemberName] string propertyName = "",
               EqualityComparer<T> equalityComparer = null)
        bool rtn = false;
        var eqComp = equalityComparer ?? EqualityComparer<T>.Default;
        if (!eqComp.Equals(field,value))
            field = value;
            rtn = true;
            if (handler != null)
                var args = new PropertyChangedEventArgs(propertyName);
                handler(sender, args);
        return rtn;

This works with .Net 4.5 because of CallerMemberNameAttribute. If you want to use it with an earlier .Net version you have to change the method declaration from: ...,[CallerMemberName] string propertyName = "", ... to ...,string propertyName, ...


public class Dog : INotifyPropertyChanged
    public event PropertyChangedEventHandler PropertyChanged;
    string _name;

    public string Name
        get { return _name; }
            this.SetPropertyAndNotify(PropertyChanged, ref _name, value);

How to enable explicit_defaults_for_timestamp?

On Windows you can run server with option key, no need to change ini files.

"C:\mysql\bin\mysqld.exe" --explicit_defaults_for_timestamp=1

Can I apply multiple background colors with CSS3?

Yes its possible! and you can use as many colors and images as you desire, here is the right way:

/* Its, very important to set the background repeat to: no-repeat */_x000D_
background-repeat:no-repeat; _x000D_
background-image:  _x000D_
/* 1) An image              */ url(, _x000D_
/* 2) Gradient              */ linear-gradient(to right, RGB(0, 0, 0), RGB(255, 255, 255)), _x000D_
/* 3) Color(using gradient) */ linear-gradient(to right, RGB(110, 175, 233), RGB(110, 175, 233));_x000D_
/* 1) Image position        */ 0 0, _x000D_
/* 2) Gradient position     */ 0 100px,_x000D_
/* 3) Color position        */ 0 130px;_x000D_
background-size:  _x000D_
/* 1) Image size            */ 640px 100px,_x000D_
/* 2) Gradient size         */ 100% 30px, _x000D_
/* 3) Color size            */ 100% 30px;_x000D_

How to query SOLR for empty fields?

One caveat! If you want to compose this via OR or AND you cannot use it in this form:


but you must use

(*:* NOT myfield:*)

This form is perfectly composable. Apparently SOLR will expand the first form to the second, but only when it is a top node. Hope this saves you some time!

Convert a string to a double - is this possible?

Why is floatval the best option for financial comparison data? bc functions only accurately turn strings into real numbers.

Beginner Python Practice?

I found python in 1988 and fell in love with it. Our group at work had been dissolved and we were looking for other jobs on site, so I had a couple of months to play around doing whatever I wanted to. I spent the time profitably learning and using python. I suggest you spend time thinking up and writing utilities and various useful tools. I've got 200-300 in my python tools library now (can't even remember them all). I learned python from Guido's tutorial, which is a good place to start (a C programmer will feel right at home).

python is also a great tool for making models -- physical, math, stochastic, etc. Use numpy and scipy. It also wouldn't hurt to learn some GUI stuff -- I picked up wxPython and learned it, as I had some experience using wxWidgets in C++. wxPython has some impressive demo stuff!

Javascript - validation, numbers only

No need for the long code for number input restriction just try this code.

It also accepts valid int & float both values.

Javascript Approach

onload =function(){ _x000D_
  var ele = document.querySelectorAll('.number-only')[0];_x000D_
  ele.onkeypress = function(e) {_x000D_
        return false;_x000D_
  ele.onpaste = function(e){_x000D_
<p> Input box that accepts only valid int and float values.</p>_x000D_
<input class="number-only" type=text />

jQuery Approach

  $('.number-only').keypress(function(e) {_x000D_
 if(isNaN(this.value+""+String.fromCharCode(e.charCode))) return false;_x000D_
  .on("cut copy paste",function(e){_x000D_
<script src=""></script>_x000D_
<p> Input box that accepts only valid int and float values.</p>_x000D_
<input class="number-only" type=text />

The above answers are for most common use case - validating input as a number.

But to allow few special cases like negative numbers & showing the invalid keystrokes to user before removing it, so below is the code snippet for such special use cases.

  $('.number-only').keyup(function(e) {_x000D_
            this.value = this.value.split('').reverse().join('').replace(/[\D]/i,'')_x000D_
    .on("cut copy paste",function(e){_x000D_
<script src=""></script>_x000D_
<p> Input box that accepts only valid int and float values.</p>_x000D_
<input class="number-only" type=text />

What's the console.log() of java?

Use the Android logging utility.

Log has a bunch of static methods for accessing the different log levels. The common thread is that they always accept at least a tag and a log message.

Tags are a way of filtering output in your log messages. You can use them to wade through the thousands of log messages you'll see and find the ones you're specifically looking for.

You use the Log functions in Android by accessing the Log.x objects (where the x method is the log level). For example:

Log.d("MyTagGoesHere", "This is my log message at the debug level here");
Log.e("MyTagGoesHere", "This is my log message at the error level here");

I usually make it a point to make the tag my class name so I know where the log message was generated too. Saves a lot of time later on in the game.

You can see your log messages using the logcat tool for android:

adb logcat

Or by opening the eclipse Logcat view by going to the menu bar

Window->Show View->Other then select the Android menu and the LogCat view

How to place div in top right hand corner of page

<style type="text/css">

You ca also use this in CSS external file.

Read file line by line using ifstream in C++

First, make an ifstream:

#include <fstream>
std::ifstream infile("thefile.txt");

The two standard methods are:

  1. Assume that every line consists of two numbers and read token by token:

    int a, b;
    while (infile >> a >> b)
        // process pair (a,b)
  2. Line-based parsing, using string streams:

    #include <sstream>
    #include <string>
    std::string line;
    while (std::getline(infile, line))
        std::istringstream iss(line);
        int a, b;
        if (!(iss >> a >> b)) { break; } // error
        // process pair (a,b)

You shouldn't mix (1) and (2), since the token-based parsing doesn't gobble up newlines, so you may end up with spurious empty lines if you use getline() after token-based extraction got you to the end of a line already.

How can I reorder a list?

>>> import random
>>> x = [1,2,3,4,5]
>>> random.shuffle(x)
>>> x
[5, 2, 4, 3, 1]

Wordpress 403/404 Errors: You don't have permission to access /wp-admin/themes.php on this server

You're in luck bud...I had the same issue but had more tech knowledge on the matter and was able to determine that it was a mod_sec issue that hostgator has to fix/whitelist on their own. You cannot do it yourself. Simply ask the hostgator tech to check mod_sec settings on your server.

Enjoy your fixed issue ;D

How can I delete all Git branches which have been merged?

My Bash script contribution is based loosely on mmrobin's answer.

It takes some useful parameters specifying includes and excludes, or to examine/remove only local or remote branches instead of both.


# exclude branches regex, configure as "(branch1|branch2|etc)$"

while [ $# -gt 0 ]; do
  case "$1" in
  -i) shift; includes="$includes $1" ;;
  -e) shift; excludes="$1" ;;
  --no-local) local=0 ;;
  --no-remote) remote=0 ;;
  --all) merged= ;;
  *) echo "Unknown argument $1"; exit 1 ;;
  shift   # next option

if [ "$includes" == "" ]; then
  includes="($(echo $includes | sed -e 's/ /|/g'))"

current_branch=$(git branch --no-color 2> /dev/null | sed -e '/^[^*]/d' -e 's/* \(.*\)/\1/')
if [ "$current_branch" != "master" ]; then
  echo "WARNING: You are on branch $current_branch, NOT master."
echo -e "Fetching branches...\n"

git remote update --prune
remote_branches=$(git branch -r $merged | grep -v "/$current_branch$" | grep -v -E "$excludes" | grep -v -E "$excludes_default" | grep -E "$includes")
local_branches=$(git branch $merged | grep -v "$current_branch$" | grep -v -E "$excludes" | grep -v -E "$excludes_default" | grep -E "$includes")
if [ -z "$remote_branches" ] && [ -z "$local_branches" ]; then
  echo "No existing branches have been merged into $current_branch."
  echo "This will remove the following branches:"
  if [ "$remote" == 1 -a -n "$remote_branches" ]; then
    echo "$remote_branches"
  if [ "$local" == 1 -a -n "$local_branches" ]; then
    echo "$local_branches"
  read -p "Continue? (y/n): " -n 1 choice
  if [ "$choice" == "y" ] || [ "$choice" == "Y" ]; then
    if [ "$remote" == 1 ]; then
      remotes=$(git remote)
      # Remove remote branches
      for remote in $remotes
        branches=$(echo "$remote_branches" | grep "$remote/" | sed "s/$remote\/\(.*\)/:\1 /g" | tr -d '\n')
        git push $remote $branches

    if [ "$local" == 1 ]; then
      # Remove local branches
      locals=$(echo "$local_branches" | sed 's/origin\///g' | tr -d '\n')
      if [ -z "$locals" ]; then
        echo "No branches removed."
        git branch -d $(echo "$locals" | tr -d '\n')

ActiveMQ connection refused

I encountered a similar problem when I was using the below to obtain connection factory ConnectionFactory factory = new

Its resolved when I changed it to the below

ConnectionFactory factory = new ActiveMQConnectionFactory("tcp://:61616");

The below then showed that my Q size was increasing.. http://:8161/admin/queues.jsp

Change the URL in the browser without loading the new page using JavaScript

There is a Yahoo YUI component (Browser History Manager) which can handle this:

How do I get Bin Path?

var path = Path.GetDirectoryName(System.Reflection.Assembly.GetExecutingAssembly().GetName().CodeBase)?.Replace("file:\\", "");

Prevent form redirect OR refresh on submit?

If you want to see the default browser errors being displayed, for example, those triggered by HTML attributes (showing up before any client-code JS treatment):

<input name="o" required="required" aria-required="true" type="text">

You should use the submit event instead of the click event. In this case a popup will be automatically displayed requesting "Please fill out this field". Even with preventDefault:

$('form').on('submit', function(event) {
   my_form_treatment(this, event);
}); // -> this will show up a "Please fill out this field" pop-up before my_form_treatment

As someone mentioned previously, return false would stop propagation (i.e. if there are more handlers attached to the form submission, they would not be executed), but, in this case, the action triggered by the browser will always execute first. Even with a return false at the end.

So if you want to get rid of these default pop-ups, use the click event on the submit button:

$('form input[type=submit]').on('click', function(event) {
   my_form_treatment(this, event);
}); // -> this will NOT show any popups related to HTML attributes

Javascript - User input through HTML input tag to set a Javascript variable?

When your script is running, it blocks the page from doing anything. You can work around this with one of two ways:

  • Use var foo = prompt("Give me input");, which will give you the string that the user enters into a popup box (or null if they cancel it)
  • Split your code into two function - run one function to set up the user interface, then provide the second function as a callback that gets run when the user clicks the button.

Using multiple parameters in URL in express

For what you want I would've used

    app.get('/fruit/:fruitName&:fruitColor', function(request, response) {
       const name = request.params.fruitName 
       const color = request.params.fruitColor 

or better yet

    app.get('/fruit/:fruit', function(request, response) {
       const fruit = request.params.fruit

where fruit is a object. So in the client app you just call{"name":"My fruit name", "color":"The color of the fruit"}

and as a response you should see:

    //  client side response
    // { name: My fruit name, color:The color of the fruit}

Guid.NewGuid() vs. new Guid()

Guid.NewGuid() creates a new UUID using an algorithm that is designed to make collisions very, very unlikely.

new Guid() creates a UUID that is all-zeros.

Generally you would prefer the former, because that's the point of a UUID (unless you're receiving it from somewhere else of course).

There are cases where you do indeed want an all-zero UUID, but in this case Guid.Empty or default(Guid) is clearer about your intent, and there's less chance of someone reading it expecting a unique value had been created.

In all, new Guid() isn't that useful due to this lack of clarity, but it's not possible to have a value-type that doesn't have a parameterless constructor that returns an all-zeros-and-nulls value.

Edit: Actually, it is possible to have a parameterless constructor on a value type that doesn't set everything to zero and null, but you can't do it in C#, and the rules about when it will be called and when there will just be an all-zero struct created are confusing, so it's not a good idea anyway.

How to center canvas in html5

Using grid?

const canvas = document.querySelector('canvas'); 
const ctx = canvas.getContext('2d'); 
ctx.fillStyle = "#FF0000";
ctx.fillRect(0, 0, canvas.width, canvas.height);
body, html {
    height: 100%;
    width: 100%;
    margin: 0;
    padding: 0;
    background-color: black;

body {
    display: grid;
    grid-template-rows: auto;
    justify-items: center;
    align-items: center;

canvas {
  height: 80vh; 
  width: 80vw; 
  display: block;