The `r` means that the string is to be treated as a raw string, which means all escape codes will be ignored.

For an example:

`&#39;\n&#39;` will be treated as a newline character, while `r&#39;\n&#39;` will be treated as the characters `\` followed by `n`.

&gt; When an `&#39;r&#39;` or `&#39;R&#39;` prefix is present,
&gt; a character following a backslash is
&gt; included in the string without change,
&gt; and all backslashes are left in the
&gt; string. For example, the string
&gt; literal `r&quot;\n&quot;` consists of two
&gt; characters: a backslash and a
&gt; lowercase `&#39;n&#39;`. String quotes can be
&gt; escaped with a backslash, but the
&gt; backslash remains in the string; for
&gt; example, `r&quot;\&quot;&quot;` is a valid string
&gt; literal consisting of two characters:
&gt; a backslash and a double quote; `r&quot;\&quot;`
&gt; is not a valid string literal (even a
&gt; raw string cannot end in an odd number
&gt; of backslashes). Specifically, a raw
&gt; string cannot end in a single
&gt; backslash (since the backslash would
&gt; escape the following quote character).
&gt; Note also that a single backslash
&gt; followed by a newline is interpreted
&gt; as those two characters as part of the
&gt; string, not as a line continuation.

Source: [Python string literals]

[Python string literals]: http://docs.python.org/reference/lexical_analysis.html#string-literals

It means that escapes won’t be translated. For example:

    r&#39;\n&#39;

is a string with a backslash followed by the letter `n`. (Without the `r` it would be a newline.)

`b` does stand for byte-string and is used in Python 3, where strings are Unicode by default. In Python 2.x strings were byte-strings by default and you’d use `u` to indicate Unicode.

Does some standard Python module contain a function to compute [modular multiplicative inverse][1] of a number, i.e. a number `y = invmod(x, p)` such that `x*y == 1 (mod p)`? Google doesn&#39;t seem to give any good hints on this.

Of course, one can come up with home-brewed 10-liner of [extended Euclidean algorithm][2], but why reinvent the wheel.

For example, Java&#39;s `BigInteger` has `modInverse` method. Doesn&#39;t Python have something similar?


  [1]: http://en.wikipedia.org/wiki/Modular_multiplicative_inverse
  [2]: http://en.wikipedia.org/wiki/Extended_Euclidean_algorithm

Modular multiplicative inverse function in Python

I need to do a market research on specific type of apps. so is there a way for me to know the download count of the app / any app.

Is there a way to find the number of downloads for a particular app in the iTunes App Store.

Find the number of downloads for a particular app in apple appstore

I first saw it used in building regular expressions across multiple lines as a method argument to `re.compile()`, so I assumed that `r` stands for RegEx.

For example:

	regex = re.compile(
		r&#39;^[A-Z]&#39;
		r&#39;[A-Z0-9-]&#39;
		r&#39;[A-Z]$&#39;, re.IGNORECASE
	)

So what does `r` mean in this case? Why do we need it?

What does preceding a string literal with &quot;r&quot; mean?

I first saw it used in building regular expressions across multiple lines as a method argument to <code>re.compile()</code>, so I assumed that <code>r</code> stands for RegEx.
For example:
<pre><code class="hljs language-python">regex = re.compile(
	r'^[A-Z]'
	r'[A-Z0-9-]'
	r'[A-Z]$', re.IGNORECASE
)
</code></pre>
So what does <code>r</code> mean in this case? Why do we need it?

I am trying to ```import Tkinter```. However, I get an error stating that ```Tkinter``` has not been installed:
```python
ImportError: No module named _tkinter, please install the python-tk package
```
I could probably install it using synaptic manager (can I?), however, I would have to install it on every machine I program on. Would it be possible to add the Tkinter library into my workspace and reference it from there?

Install tkinter for Python

I&#39;m trying to get the links from a page with xpath. The problem is that I only want the links inside a table, but if I apply the xpath expression on the whole page I&#39;ll capture links which I don&#39;t want.

For example:

    tree = lxml.html.parse(some_response)
    links = tree.xpath(&quot;//a[contains(@href, &#39;http://www.example.com/filter/&#39;)]&quot;)

The problem is that applies the expression to the whole document. I located the element I want, for example:

    tree = lxml.html.parse(some_response)
    root = tree.getroot()
    table = root[1][5] #for example
    links = table.xpath(&quot;//a[contains(@href, &#39;http://www.example.com/filter/&#39;)]&quot;)

But that seems to be performing the query in the whole document as well, as I still am capturing the links outside of the table. &lt;a href=&quot;http://codespeak.net/lxml/xpathxslt.html&quot;&gt;This page&lt;/a&gt; says that &quot;When xpath() is used on an Element, the XPath expression is evaluated against the element (if relative) or against the root tree (if absolute):&quot;. So, what I using is an absolute expression and I need to make it relative? Is that it?

Basically, how can I go about filtering only elements that exist inside of this table?

Python: Using xpath locally / on a specific element

I created a custom group in Django&#39;s admin site.

In my code, I want to check if a user is in this group. How do I do that?

In Django, how do I check if a user is in a certain group?

I&#39;m launching a subprocess with the following command:

    p = subprocess.Popen(cmd, stdout=subprocess.PIPE, shell=True)

However, when I try to kill using:

    p.terminate()

or 

    p.kill()

The command keeps running in the background, so I was wondering how can I actually terminate the process. 

Note that when I run the command with:

    p = subprocess.Popen(cmd.split(), stdout=subprocess.PIPE)

It does terminate successfully when issuing the `p.terminate()`.


How to terminate a python subprocess launched with shell=True

I would like to create a copy of an object. I want the new object to possess all properties of the old object (values of the fields). But I want to have independent objects. So, if I change values of the fields of the new object, the old object should not be affected by that.

How can I create a copy of an object in Python?

What is the difference between `null` and the `&quot;&quot;` (empty string)?

I have written some simple code:

    String a = &quot;&quot;;
    String b = null;
    
    System.out.println(a == b); // false
    System.out.println(a.equals(b)); // false

Both statements return `false`. It seems, I am not able to find what is the actual difference between them.

Difference between null and empty (&quot;&quot;) Java String

I&#39;m wondering how Python does string comparison, more specifically how it determines the outcome when a less than `&lt;` or greater than `&gt;` operator is used.

For instance if I put `print(&#39;abc&#39; &lt; &#39;bac&#39;)` I get `True`. I understand that it compares corresponding characters in the string, however its unclear as to why there is more, for lack of a better term, &quot;weight&quot; placed on the fact that `a` is less than`b` (first position) in first string rather than the fact that `a` is less than `b` in the second string (second position).

How are strings compared?

I&#39;ve seen many developers use different methods to split a string by new lines, but i&#39;m confused which is the correct: `\r\n` OR `\n` only?

Is a new line = \n OR \r\n?

I need javascript to add 5 to an integer variable, but instead it treats the variable as a string, so it write out the variable, then add 5 onto the end of the &quot;string&quot;. How can I force it to do math instead?

    var dots = document.getElementById(&quot;txt&quot;).value; // 5
    function increase(){
        dots = dots + 5;
    }
   
Output: `55`

How can I force it to output `10`?

How to force JS to do math instead of putting two strings together

I would like to convert a string array to a single string.

    string[] test = new string[2];
    test[0] = &quot;Hello &quot;;
    test[1] = &quot;World!&quot;;

I would like to have something like &quot;Hello World!&quot;

convert string array to string

How do you write a comment in Markdown, i.e. text that is not rendered in the HTML output? I found nothing on the [Markdown project][1].


  [1]: http://daringfireball.net/projects/markdown/

Comments in Markdown

I saw `1/3.f` in a program and wondered what the `.f` was for. So tried my own program:

    #include &lt;iostream&gt;

    int main()
    {
        std::cout &lt;&lt; (float) 1/3 &lt;&lt; std::endl;
        std::cout &lt;&lt; 1/3.f &lt;&lt; std::endl;
        std::cout &lt;&lt; 1/3 &lt;&lt; std::endl;
    }

Is the `.f` used like a cast? Is there a place where I can read more about this interesting syntax?




Purpose of a &quot;.f&quot; appended to a number?

I was reading through some JMockit examples and found this code:

    final List&lt;OrderItem&gt; actualItems = new ArrayList&lt;~&gt;();

What does the tilde in the generic identifier mean? I know it&#39;s the unary bitwise NOT operator, but I don&#39;t see an operand here.

Also, I tried compiling it and got an error. Am I just missing something?

What does a tilde in angle brackets mean when creating a Java generic class?

Other than the obvious fact that the first form could use a variable and not just a string literal, is there any reason to use one over the other, and if so under which cases?

In code:

    // Given:
    var foo = {&#39;bar&#39;: &#39;baz&#39;};

    // Then
    var x = foo[&#39;bar&#39;];

    // vs. 
    var x = foo.bar;

Context: I&#39;ve written a code generator which produces these expressions and I&#39;m wondering which is preferable.

JavaScript property access: dot notation vs. brackets?

I find it more convenient to access dict keys as `obj.foo` instead of `obj[&#39;foo&#39;]`, so I wrote this snippet:

    class AttributeDict(dict):
        def __getattr__(self, attr):
            return self[attr]
        def __setattr__(self, attr, value):
            self[attr] = value

However, I assume that there must be some reason that Python doesn&#39;t provide this functionality out of the box. What would be the caveats and pitfalls of accessing dict keys in this manner?

Accessing dict keys like an attribute?

I currently have a WebSocket between JavaScript and a server programmed in C#. In JavaScript, I can pass data easily using an associative array:

    var data = {&#39;test&#39;: &#39;val&#39;,
                &#39;test2&#39;: &#39;val2&#39;};

To represent this data object on the server side, I use a `Dictionary&lt;string, string&gt;`, but this is more &#39;typing-expensive&#39; than in JavaScript:

    Dictionary&lt;string, string&gt; data = new Dictionary&lt;string,string&gt;();
    data.Add(&quot;test&quot;, &quot;val&quot;);
    data.Add(&quot;test2&quot;, &quot;val2&quot;);

Is there some kind of literal notation for associative arrays / `Dictionary`s in C#?

Literal notation for Dictionary in C#?

If I have a method 

    void f(byte b);

how can I call it with a numeric argument without casting?

    f(0);

gives an error.


How do you specify a byte literal in Java?

I am working on a (Java) project in which I have many jars which have a source-jar file attached.
 
Is there any way to make the eclipse &quot;File Search&quot; search for Java files (and txt, xml etc. for that matter) containing some string literal inside these source jars, not just in the project folder?

Or is there any plugin by which this can be achieved?

How to make eclipse &quot;File Search&quot; to also search inside source jars containing some text?

I&#39;ve got a (generated) literal string in C++ that may contain characters that need to be escaped using the `\x` notation. For example:

    char foo[] = &quot;\xABEcho&quot;;

However, g++ (version 4.1.2 if it matters) throws an error:

    test.cpp:1: error: hex escape sequence out of range

The compiler appears to be considering the `Ec` characters as part of the preceding hex number (because they look like hex digits). Since a four digit hex number won&#39;t fit in a `char`, an error is raised. Obviously for a wide string literal `L&quot;\xABEcho&quot;` the first character would be U+ABEC, followed by `L&quot;ho&quot;`.

It seems this has changed sometime in the past couple of decades and I never noticed. I&#39;m almost certain that old C compilers would only consider *two* hex digits after `\x`, and not look any further.

I can think of one workaround for this:

    char foo[] = &quot;\xAB&quot;&quot;Echo&quot;;

but that&#39;s a bit ugly. So I have three questions:

- When did this change?

- Why doesn&#39;t the compiler only accept &gt;2-digit hex escapes for wide string literals?

- Is there a workaround that&#39;s less awkward than the above?

When did C++ compilers start considering more than two hex digits in string literal character escapes?


In C/C#/etc. you can tell the compiler that a literal number is not what it appears to be (ie., `float` instead of `double`, `unsigned long` instead of `int`): 
```C#
var d = 1.0;  // double
var f = 1.0f; // float
var u = 1UL;  // unsigned long
```
etc.

Could someone point me to a list of these? I&#39;m specifically looking for a suffix for `short` or `Int16`.



C# short/long/int literal format?

I&#39;m trying to parse a json response data from youtube api but i keep getting an error.

Here is the snippet where it choking:

    data = json.loads(&quot;&quot;&quot;{ &quot;entry&quot;:{ &quot;etag&quot;:&quot;W/\&quot;A0UGRK47eCp7I9B9WiRrYU0.\&quot;&quot; } }&quot;&quot;&quot;)
..and this happens:

    JSONDecodeError: Expecting , delimiter: line 1 column 23 (char 23)

I&#39;ve confirmed that it&#39;s valid json and I have no control over the formatting of it so how can I get past this error?

Valid JSON giving JSONDecodeError: Expecting , delimiter

From the python documentation on [regex][1], regarding the `&#39;\&#39;` character:

&gt; The solution is to use Python’s raw string notation for regular
&gt; expression patterns; backslashes are not handled in any special way in
&gt; a string literal prefixed with `&#39;r&#39;`. So `r&quot;\n&quot;` is a two-character string
&gt; containing `&#39;\&#39;` and `&#39;n&#39;`, while `&quot;\n&quot;` is a one-character string
&gt; containing a newline. Usually patterns will be expressed in Python
&gt; code using this raw string notation.

What is this raw string notation? If you use a raw string format, does that mean `&quot;*&quot;` is taken as a a literal character rather than a zero-or-more indicator? That obviously can&#39;t be right, or else regex would completely lose its power. But then if it&#39;s a raw string, how does it recognize newline characters if `&quot;\n&quot;` is literally a backslash and an `&quot;n&quot;`?

I don&#39;t follow.

**Edit for bounty:**

I&#39;m trying to understand how a raw string regex matches newlines, tabs, and character sets, e.g. `\w` for words or `\d` for digits or all whatnot, if raw string patterns don&#39;t recognize backslashes as anything more than ordinary characters. I could really use some good examples.


  [1]: https://docs.python.org/library/re.html

What exactly is a &quot;raw string regex&quot; and how can you use it?

The two characters `)&quot;` terminate the raw string literal in the example below. &lt;br&gt;
The sequence `)&quot;` could appear in my text at some point, and I want the string to continue even if this sequence is found within it.

    R&quot;(  
        Some Text)&quot;  
    )&quot;;       // ^^
   

How can I include the sequence `)&quot;` within the string literal without terminating it?

Content Type	Original Author	Original Content on Stackoverflow
Question	Nikki Erwin Ramirez	View Question on Stackoverflow
Solution 1 - Python	Sebastian Paaske Tørholm	View Answer on Stackoverflow
Solution 2 - Python	Nate	View Answer on Stackoverflow

What does preceding a string literal with "r" mean?

Python Problem Overview

Python Solutions

Solution 1 - Python

Solution 2 - Python

Find the number of downloads for a particular app in apple appstore

Modular multiplicative inverse function in Python

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