Have a look at [`re.sub`][1]:

    result = re.sub(r&quot;(\d.*?)\s(\d.*?)&quot;, r&quot;\1 \2&quot;, string1)

This is Python&#39;s regex substitution (replace) function. The replacement string can be filled with so-called backreferences (backslash, group number) which are replaced with what was matched by the groups. Groups are counted the same as by the `group(...)` function, i.e. starting from `1`, from left to right, by opening parentheses.  

  [1]: http://docs.python.org/2/library/re.html#re.sub

The accepted answer is perfect. I would add that group reference is probably better achieved by using this syntax:

    r&quot;\g&lt;1&gt; \g&lt;2&gt;&quot;

for the replacement string. This way, you work around syntax limitations where a group may be followed by a digit. Again, this is all present in the doc, nothing new, just sometimes difficult to spot at first sight.

We are using Selenium to automate our `UI` testing. Recently we have seen majority of our users using Chrome. So we wanted to know - pros and cons of using PhantomJS vs Selenium:

 - Is there any real advantage in terms of performance, e.g. time taken to execute the test cases?
 - When should one prefer PhantomJS over Selenium?

Casperjs/PhantomJs vs Selenium

In angularjs you have the [tag ng-src](http://docs.angularjs.org/api/ng.directive:ngSrc) which has the purpose that you won&#39;t receive an error for an invalid url before angularjs gets to evaluate the variables placed in between `{{` and `}}`.

The problem is that I use quite some DIV&#39;s with a `background-image` set to an url. I do this because of the excellent CSS3 property `background-size` which crops the image to the exact size of the DIV.

The only problem is that I receive a lot of errors for the exact same reason they created a ng-src tag: I have some variables in the url and the browser thinks the image doesn&#39;t exist.

I realize that there is a possibility of writing a crude `{{&quot;style=&#39;background-image:url(myVariableUrl)&#39;&quot;}}`, but this seems &#39;dirty&#39;.

I&#39;ve searched a lot and can&#39;t find the right way to do this. My app is becoming a mess because of all of these errors.



angularjs: ng-src equivalent for background-image:url(...)

Is there any way to directly replace all groups using regex syntax?

The normal way:

    re.match(r&quot;(?:aaa)(_bbb)&quot;, string1).group(1)

But I want to achieve something like this:

    re.match(r&quot;(\d.*?)\s(\d.*?)&quot;, &quot;(CALL_GROUP_1) (CALL_GROUP_2)&quot;)

I want to build the new string instantaneously from the groups the Regex just captured.

Python Regex instantly replace groups

Is there any way to directly replace all groups using regex syntax?
The normal way:
<pre><code class="hljs language-python">re.match(r"(?:aaa)(_bbb)", string1).group(1)
</code></pre>
But I want to achieve something like this:
<pre><code class="hljs language-python">re.match(r"(\d.*?)\s(\d.*?)", "(CALL_GROUP_1) (CALL_GROUP_2)")
</code></pre>
I want to build the new string instantaneously from the groups the Regex just captured.

I get the following error when trying to run Django from the command line.

    File manage.py, line 8, in &lt;module&gt;
    &#160;&#160;&#160;&#160; from django.core.management import execute_from_command_line
    ImportError: No module named django.core.management
    

Any ideas on how to solve this?



Django - &quot;no module named django.core.management&quot;

I am writing a script in Python (.py file) and I am using Matplotlib to plot an array.
I want to add a legend with a formula to the plot, but I haven&#39;t been able to do it.
I have done this before in IPython or the terminal. In this case, writing something like this:

    legend(ur&#39;$The_formula$&#39;)
worked perfectly. However, this doesn&#39;t work when I call my .py script from the terminal/IPython.

How do I write a Latex formula in the legend of a plot using Matplotlib inside a .py file?

I have a pandas DataFrame like this:

                        a         b
    2011-01-01 00:00:00 1.883381  -0.416629
    2011-01-01 01:00:00 0.149948  -1.782170
    2011-01-01 02:00:00 -0.407604 0.314168
    2011-01-01 03:00:00 1.452354  NaN
    2011-01-01 04:00:00 -1.224869 -0.947457
    2011-01-01 05:00:00 0.498326  0.070416
    2011-01-01 06:00:00 0.401665  NaN
    2011-01-01 07:00:00 -0.019766 0.533641
    2011-01-01 08:00:00 -1.101303 -1.408561
    2011-01-01 09:00:00 1.671795  -0.764629

Is there an efficient way to find the &quot;integer&quot; index of rows with NaNs? In this case the desired output should be `[3, 6]`.

Find integer index of rows with NaN in pandas dataframe

Is there a way in Python to pass optional parameters to a function while calling it and in the function definition have some code based on &quot;only if the optional parameter is passed&quot;




Is there a way to pass optional parameters to a function?

I am working with Flask 0.9. 

Now I want to route three urls to the same function:

    /item/&lt;int:appitemid&gt;
    /item/&lt;int:appitemid&gt;/ 
    /item/&lt;int:appitemid&gt;/&lt;anything can be here&gt;

The `&lt;anything can be here&gt;` part will never be used in the function.

I have to copy the same function twice to achieve this goal:

    @app.route(&#39;/item/&lt;int:appitemid&gt;/&#39;)
    def show_item(appitemid):
    
    @app.route(&#39;/item/&lt;int:appitemid&gt;/&lt;path:anythingcanbehere&gt;&#39;)
    def show_item(appitemid, anythingcanbehere):

Will there be a better solution?


Flask URL Route: Route Several URLs to the same function

I am facing an issue with URLs, I want to be able to convert titles that could contain anything and have them stripped of all special characters so they only have letters and numbers and of course I would like to replace spaces with hyphens.

How would this be done? I&#39;ve heard a lot about regular expressions (regex) being used...

Remove all special characters from a string

What regular expression engine does Nginx use? [There are a lot of possibilities.](http://www.regular-expressions.info/refflavors.html) More to the point, what flavor of syntax does it support, that is, what syntax features can I make use of?

What regular expression engine does Nginx use?

I am trying to create an application that matches a message template with a message that a user is trying to send. I am using Java regex for matching the message. The template/message may contain special characters.

How would I get the complete list of special characters that need to be escaped in order for my regex to work and match in the maximum possible cases?

Is there a universal solution for escaping all special characters in Java regex?

List of all special characters that need to be escaped in a regex

hi i would like to understand why the following code which does a split string split using regex

    #include&lt;regex&gt;
    #include&lt;vector&gt;
    #include&lt;string&gt;
    
    std::vector&lt;std::string&gt; split(const std::string &amp;s){
        static const std::regex rsplit(&quot; +&quot;);
        auto rit = std::sregex_token_iterator(s.begin(), s.end(), rsplit, -1);
        auto rend = std::sregex_token_iterator();
        auto res = std::vector&lt;std::string&gt;(rit, rend);
        return res;
    }
    
    int main(){
        for(auto i=0; i&lt; 10000; ++i)
           split(&quot;a b c&quot;, &quot; &quot;);
        return 0;
    }

is slower then the following python code

    import re
    for i in range(10000):
        re.split(&#39; +&#39;, &#39;a b c&#39;)

here&#39;s 


    &gt; python test.py  0.05s user 0.01s system 94% cpu 0.070 total
    ./test  0.26s user 0.00s system 99% cpu 0.296 total

Im using clang++ on osx.

compiling with -O3 brings it to  down to `0.09s user 0.00s system 99% cpu 0.109 total`

c++11 regex slower than python

I have the following code which looks through the files in one directory and copies files that contain a certain string into another directory, but I am trying to use Regular Expressions as  the string could be upper and lowercase or a mix of both. 

Here is the code that works, before I tried to use RegEx&#39;s

    import os
    import re
    import shutil
    
    def test():
        os.chdir(&quot;C:/Users/David/Desktop/Test/MyFiles&quot;)
        files = os.listdir(&quot;.&quot;)
        os.mkdir(&quot;C:/Users/David/Desktop/Test/MyFiles2&quot;)
        for x in (files):
            inputFile = open((x), &quot;r&quot;)
            content = inputFile.read()
            inputFile.close()
            if (&quot;Hello World&quot; in content)
                shutil.copy(x, &quot;C:/Users/David/Desktop/Test/MyFiles2&quot;)

Here is my code when I have tried to use RegEx&#39;s

    import os
    import re
    import shutil
    
    def test2():
        os.chdir(&quot;C:/Users/David/Desktop/Test/MyFiles&quot;)
        files = os.listdir(&quot;.&quot;)
        os.mkdir(&quot;C:/Users/David/Desktop/Test/MyFiles2&quot;)
        regex_txt = &quot;facebook.com&quot;
        for x in (files):
            inputFile = open((x), &quot;r&quot;)
            content = inputFile.read()
            inputFile.close()
            regex = re.compile(regex_txt, re.IGNORECASE)

Im guessing that I need a line of code that is something like

    if regex = re.compile(regex_txt, re.IGNORECASE) == True

But I cant seem to get anything to work, if someone could point me in the right direction it would be appreciated. 

Python: How to use RegEx in an if statement?

I am using this regex:

    ((?:[a-z][a-z]+))_(\d+)_((?:[a-z][a-z]+)\d+)_(\d{13})

to match strings like this:

    SH_6208069141055_BC000388_20110412101855

separating into 4 groups:   

    SH
    6208069141055
    BC000388
    20110412101855

**Question:** How do I make the first group optional, so that the resulting group is a empty string?  
I want to get 4 groups in every case, when possible.

Input string for this case: (no underline after the first group)

    6208069141055_BC000388_20110412101855


Regex optional group

I have a list of words:

    bau
    ceu
    diu
    fou
    gau

I want to turn that list into:

    byau
    cyeu
    dyiu
    fyou
    gyau

I unsuccessfully tried the command:

    :%s/(\w)(\w\w)/\1y\2/g

Given that this doesn&#39;t work, what do I have to change to make the regex capture groups work in Vim?

Content Type	Original Author	Original Content on Stackoverflow
Question	user1467267	View Question on Stackoverflow
Solution 1 - Python	Martin Ender	View Answer on Stackoverflow
Solution 2 - Python	benelgiac	View Answer on Stackoverflow

Python Regex instantly replace groups

Python Problem Overview

Python Solutions

Solution 1 - Python

Solution 2 - Python

angularjs: ng-src equivalent for background-image:url(...)

Casperjs/PhantomJs vs Selenium

Attributions