### python-dev
`python-dev` contains the *header files* you need **to build *Python extensions***.

### lxml
`lxml` is a **Python C-API extension** that is compiled when you do `pip install lxml`. The lxml sources have at least something like `#include &lt;Python.h&gt;` in the code. The compiler looks for the *header file* `Python.h` during compilation, hence those *header files* need to be on your system such that they can be found.

### `-dev` packages on Linux
On Linux typically, the *binary libraries* and *header files* of packages like *Python* are separate. Hence you can have Python (e.g. package `python`) installed and everything works fine. But when you want to build *extensions* you need to install the corresponding `-dev` package.

`python-dev` is the package that contains the header files for the Python C API, which is used by `lxml` because it includes Python C extensions for high performance.

python-dev contains everything needed to compile python extension modules (https://docs.python.org/2/extending/extending.html).

Note that Debian already has an lxml package for python 3 (mentioned at http://lxml.de/installation.html); in general it&#39;s a good idea to use the packaged version. I&#39;d suggest `pip uninstall lxml` and then `apt-get install python3-lxml`.

In [this Spring Boot application][1] there is a web service, which returns some data for a logged-in user:

    @RequestMapping(&quot;/resource&quot;)
    public Map&lt;String, Object&gt; home() {
    	Map&lt;String, Object&gt; model = new HashMap&lt;String, Object&gt;();
    	model.put(&quot;id&quot;, UUID.randomUUID().toString());
    	model.put(&quot;content&quot;, &quot;Hello World&quot;);
    	return model;
    }

Imagine, the return value of the method depends on what user is currently logged in.

How can I find out, which user is logged in in that method?


  [1]: https://github.com/dsyer/spring-security-angular/blob/master/single/src/main/java/demo/UiApplication.java

How to find out the currently logged-in user in Spring Boot?

I want to add space between two slick carousel items, but not want the space with padding, because it&#39;s reducing my element size(and I don&#39;t want that).

![enter image description here][1]


&lt;!-- begin snippet: js hide: false --&gt;

&lt;!-- language: lang-js --&gt;

        $(&#39;.single-item&#39;).slick({
            initialSlide: 3,
            infinite: false
        });

&lt;!-- language: lang-css --&gt;

    .slick-slider {
        margin:0 -15px;
    }
    .slick-slide {
        padding:10px;
        background-color:red;
        text-align:center;
        margin-right:15px;
        margin-left:15px;
    }

&lt;!-- language: lang-html --&gt;

    &lt;script src=&quot;https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/js/bootstrap.min.js&quot;&gt;&lt;/script&gt;
    &lt;link href=&quot;https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap.min.css&quot; rel=&quot;stylesheet&quot;/&gt;
    &lt;script src=&quot;http://cdn.jsdelivr.net/jquery.slick/1.5.0/slick.min.js&quot;&gt;&lt;/script&gt;
    &lt;link href=&quot;http://cdn.jsdelivr.net/jquery.slick/1.5.0/slick.css&quot; rel=&quot;stylesheet&quot;/&gt;
    &lt;script src=&quot;https://ajax.googleapis.com/ajax/libs/jquery/1.11.0/jquery.min.js&quot;&gt;&lt;/script&gt;
    &lt;div class=&quot;container&quot;&gt;
        &lt;div class=&quot;row&quot;&gt;
            &lt;div class=&quot;col-sm-12&quot; style=&quot;background-color:gray;&quot;&gt;
                &lt;div class=&quot;slider single-item&quot; style=&quot;background:yellow&quot;&gt;
                    &lt;div&gt;1&lt;/div&gt;
                    &lt;div&gt;2&lt;/div&gt;
                    &lt;div&gt;3&lt;/div&gt;
                    &lt;div&gt;4&lt;/div&gt;
                    &lt;div&gt;5&lt;/div&gt;
                    &lt;div&gt;6&lt;/div&gt;
                &lt;/div&gt;
            &lt;/div&gt;
        &lt;/div&gt;
    &lt;/div&gt;

&lt;!-- end snippet --&gt;
   
Somehow I am getting space from both side, I am trying to remove that.

  [1]: http://i.stack.imgur.com/mE5XN.png
  [2]: http://jsfiddle.net/363ph8q8/4/


How add spaces between Slick carousel item

I recently installed `lxml`.

Before that, I had to install all the dependencies for that.
So I tried to install `liblxml2-dev`, `liblxslt1-dev` and `python-dev`
(google-searched for what packages are required for `lxml`)
but even after that, I could not able to install `lxml` by using the command
`pip install lxml`.

However as because I am using Python 3.4.0, I thought that may be there are different version of `python-dev` (thought came due to facing some similar version conflict problem). So I tried to install `python3-dev`.

Then I tried to install `lxml` using the same command said earlier and that worked!!!

I google-searched for those sentences
and I could able to understand the meaning of `lxml` and `xslt`. I found a [link][1] for `python-dev` but I am not still sure what it is actually doing.

OS - Ubuntu

  [1]: https://packages.debian.org/sid/python-dev

What is python-dev package used for

I recently installed <code>lxml</code>.
Before that, I had to install all the dependencies for that.
So I tried to install <code>liblxml2-dev</code>, <code>liblxslt1-dev</code> and <code>python-dev</code>
(google-searched for what packages are required for <code>lxml</code>)
but even after that, I could not able to install <code>lxml</code> by using the command
<code>pip install lxml</code>.
However as because I am using Python 3.4.0, I thought that may be there are different version of <code>python-dev</code> (thought came due to facing some similar version conflict problem). So I tried to install <code>python3-dev</code>.
Then I tried to install <code>lxml</code> using the same command said earlier and that worked!!!
I google-searched for those sentences
and I could able to understand the meaning of <code>lxml</code> and <code>xslt</code>. I found a <a href="https://packages.debian.org/sid/python-dev" target="_blank" rel="noopener noreferrer">link</a> for <code>python-dev</code> but I am not still sure what it is actually doing.
OS - Ubuntu

    @app.route(&#39;/view&#39;, methods=[&#39;GET&#39;, &#39;POST&#39;])
    def view_notifications():
        posts = get_notifications()
        return render_template(&quot;frontend/src/view_notifications.html&quot;, posts=posts)

So in my `project/backend/src/app.py` there&#39;s this code. How would I reference the template that&#39;s in `project/frontend/src/view_notifications.html` I&#39;ve tried using `..` but it keeps saying the path isn&#39;t found. Is there another way I should be doing this?


    [Tue Jun 23 12:56:02.597207 2015] [wsgi:error] [pid 2736:tid 140166294406912] [remote 10.0.2.2:248] TemplateNotFound: frontend/src/view_notifications.html
    [Tue Jun 23 12:56:05.508462 2015] [mpm_event:notice] [pid 2734:tid 140166614526016] AH00491: caught SIGTERM, shutting down

How to reference a html template from a different directory in python flask

After installing a package in an anaconda environment, I&#39;ll like to make some changes to the code in that package.

Where can I find the `site-packages` directory containing the installed packages? I do not find a directory `/Users/username/anaconda/lib/python2.7/site-packages`

Anaconda site-packages

I am trying to learn how to automatically fetch urls from a page. In the following code I am trying to get the title of the webpage:

    import urllib.request
    import re
    
    url = &quot;http://www.google.com&quot;
    regex = r&#39;&lt;title&gt;(,+?)&lt;/title&gt;&#39;
    pattern  = re.compile(regex)
    
    with urllib.request.urlopen(url) as response:
       html = response.read()
    
    title = re.findall(pattern, html)
    print(title)

And I get this unexpected error:

    Traceback (most recent call last):
      File &quot;path\to\file\Crawler.py&quot;, line 11, in &lt;module&gt;
        title = re.findall(pattern, html)
      File &quot;C:\Python33\lib\re.py&quot;, line 201, in findall
        return _compile(pattern, flags).findall(string)
    TypeError: can&#39;t use a string pattern on a bytes-like object

What am I doing wrong?


TypeError: can&#39;t use a string pattern on a bytes-like object in re.findall()

What is the difference between these two lines of code:

    if not x == &#39;val&#39;:
and 

    if x != &#39;val&#39;:


Is one more efficient than the other?


Would it be better to use

    if x == &#39;val&#39;:
        pass
    else:


Python if not == vs if !=

I need to extract a gz file that I have downloaded from an FTP site to a local Windows file server. I have the variables set for the local path of the file, and I know it can be used by GZIP muddle. 

How can I do this? The file inside the GZ file is an XML file. 


How to unzip gz file using Python

I&#39;m trying to compile miniSAT on Kali Linux 64 bits but I keep getting the error message:

&gt; fatal error: zlib.h: no such file or directory

I have read that there might be a linking problem that makes the compiler unable to find the header files, but I&#39;m new to Linux and do not know how to solve that.

How to fix fatal error: zlib.h: no such file or directory?

Surprisingly, I find `startswith` is slower than `in`:

    In [10]: s=&quot;ABCD&quot;*10

    In [11]: %timeit s.startswith(&quot;XYZ&quot;)
    1000000 loops, best of 3: 307 ns per loop
    
    In [12]: %timeit &quot;XYZ&quot; in s
    10000000 loops, best of 3: 81.7 ns per loop

As we all know, the `in` operation needs to search the whole string and `startswith` just needs to check the first few characters, so `startswith` should be more efficient.

When `s` is big enough, `startswith` is faster:

    In [13]: s=&quot;ABCD&quot;*200
    
    In [14]: %timeit s.startswith(&quot;XYZ&quot;)
    1000000 loops, best of 3: 306 ns per loop
    
    In [15]: %timeit &quot;XYZ&quot; in s
    1000000 loops, best of 3: 666 ns per loop

So it seems that calling `startswith` has some overhead which makes it slower when the string is small.

And than I tried to figure out what&#39;s the overhead of the `startswith` call.
    
First, I used an `f` variable to reduce the cost of the dot operation - as mentioned in this [answer][1] - here we can see `startswith` is still slower:

    In [16]: f=s.startswith
    
    In [17]: %timeit f(&quot;XYZ&quot;)
    1000000 loops, best of 3: 270 ns per loop

Further, I tested the cost of an empty function call:

    In [18]: def func(a): pass
    
    In [19]: %timeit func(&quot;XYZ&quot;)
    10000000 loops, best of 3: 106 ns per loop

Regardless of the cost of the dot operation and function call, the time of `startswith` is about (270-106)=164ns, but the `in` operation takes only 81.7ns. It seems there are still some overheads for `startswith`, what&#39;s that?

Add the test result between `startswith` and `__contains__` as suggested by poke and lvc:

    In [28]: %timeit s.startswith(&quot;XYZ&quot;)
    1000000 loops, best of 3: 314 ns per loop
    
    In [29]: %timeit s.__contains__(&quot;XYZ&quot;)
    1000000 loops, best of 3: 192 ns per loop


  [1]: https://stackoverflow.com/a/13271125/552942

Why is string&#39;s startswith slower than in?

I have encountered this weird behavior and failed to explain it. These are the benchmarks:

    py -3 -m timeit &quot;tuple(range(2000)) == tuple(range(2000))&quot;
    10000 loops, best of 3: 97.7 usec per loop
    py -3 -m timeit &quot;a = tuple(range(2000));  b = tuple(range(2000)); a==b&quot;
    10000 loops, best of 3: 70.7 usec per loop

How come comparison with variable assignment is faster than using a one liner with temporary variables by more than 27%?

By the Python docs, garbage collection is disabled during timeit so it can&#39;t be that. Is it some sort of an optimization?

The results may also be reproduced in Python 2.x though to lesser extent.

Running Windows 7/10, CPython 3.5.1 all the way to 3.10.1, Intel i7 3.40 GHz, 64 bit both OS and Python. Seems like a different machine I&#39;ve tried running at Intel i7 3.60 GHz with Python 3.5.0 does not reproduce the results.

----------

Running using the same Python process with `timeit.timeit()` @ 10000 loops produced 0.703 and 0.804 respectively. Still shows although to lesser extent. (~12.5%)

Why is code using intermediate variables faster than code without?

So i was playing with `list` objects and found little strange thing that if `list` is created with `list()` it uses more memory, than list comprehension? I&#39;m using Python 3.5.2

    In [1]: import sys
    In [2]: a = list(range(100))
    In [3]: sys.getsizeof(a)
    Out[3]: 1008
    In [4]: b = [i for i in range(100)]
    In [5]: sys.getsizeof(b)
    Out[5]: 912
    In [6]: type(a) == type(b)
    Out[6]: True
    In [7]: a == b
    Out[7]: True
    In [8]: sys.getsizeof(list(b))
    Out[8]: 1008

From the [docs](https://docs.python.org/3.5/library/stdtypes.html#list):

&gt; Lists may be constructed in several ways:
&gt;
&gt; - Using a pair of square brackets to denote the empty list: `[]`
&gt; - Using square brackets, separating items with commas: `[a]`, `[a, b, c]`
&gt; - Using a list comprehension: `[x for x in iterable]`
&gt; - Using the type constructor: `list()` or `list(iterable)`


But it seems that using `list()` it uses more memory.

And as much `list` is bigger, the gap increases.

[![Difference in memory][1]][1]

Why this happens?

**UPDATE #1**

Test with Python 3.6.0b2:

    Python 3.6.0b2 (default, Oct 11 2016, 11:52:53) 
    [GCC 5.4.0 20160609] on linux
    Type &quot;help&quot;, &quot;copyright&quot;, &quot;credits&quot; or &quot;license&quot; for more information.
    &gt;&gt;&gt; import sys
    &gt;&gt;&gt; sys.getsizeof(list(range(100)))
    1008
    &gt;&gt;&gt; sys.getsizeof([i for i in range(100)])
    912

**UPDATE #2**

Test with Python 2.7.12:

    Python 2.7.12 (default, Jul  1 2016, 15:12:24) 
    [GCC 5.4.0 20160609] on linux2
    Type &quot;help&quot;, &quot;copyright&quot;, &quot;credits&quot; or &quot;license&quot; for more information.
    &gt;&gt;&gt; import sys
    &gt;&gt;&gt; sys.getsizeof(list(xrange(100)))
    1016
    &gt;&gt;&gt; sys.getsizeof([i for i in xrange(100)])
    920

  [1]: https://i.stack.imgur.com/VVHJL.png

list() uses slightly more memory than list comprehension

Everything in Python is an object. So the size of an int in Python will be larger than usual.

    &gt;&gt;&gt; sys.getsizeof(int())
    24

OK, but why does it take 12 more bytes for `2⁶&#179;` compared too `2⁶&#179; - 1` and not just one?

    &gt;&gt;&gt; sys.getsizeof(2**63)
    36
    &gt;&gt;&gt; sys.getsizeof(2**62)
    24

I get that `2⁶&#179;` is a long and `2⁶&#179;-1` an int, but why 12 bytes of difference?

No more intuitive, I tried some other things:

    &gt;&gt;&gt; a = 2**63
    &gt;&gt;&gt; a -= 2**62
    &gt;&gt;&gt; sys.getsizeof(a)
    36

`a` is still stored as a long even if it could be in an int now. So that&#39;s not surprising. But:

    &gt;&gt;&gt; a -= (2**63 - 1)
    &gt;&gt;&gt; a = 2**63
    &gt;&gt;&gt; a -= (2**63 - 1)
    &gt;&gt;&gt; a
    1L
    &gt;&gt;&gt; sys.getsizeof(a)
    28

A new size.

    &gt;&gt;&gt; a = 2**63
    &gt;&gt;&gt; a -= 2**63
    &gt;&gt;&gt; a
    0L
    &gt;&gt;&gt; sys.getsizeof(a)
    24

Back to 24 bytes, but still with a long.

Last thing I got:

    &gt;&gt;&gt; sys.getsizeof(long())
    24

**Question:**

How does the memory storage work in those scenarios?

**Sub-questions:**

Why is there a gap of 12 bytes to add what our intuition tells us is just 1 bit?

Why are `int()` and `long()` 24 bytes, but `long(1)` is already 28 bytes and `int(2⁶&#178;)`?

*NB: Python 3.X is working a bit differently, but not more intuitively. Here I focused on Python 2.7; I did not test on prior versions.*


Why is the size of 2⁶&#179; 36 bytes, but 2⁶&#179;-1 is only 24 bytes?

Experimenting with magic methods (`__sizeof__` in particular) on different Python objects I stumbled over the following behaviour:

Python 2.7

    &gt;&gt;&gt; False.__sizeof__()
    24
    &gt;&gt;&gt; True.__sizeof__()
    24

Python 3.x

    &gt;&gt;&gt; False.__sizeof__()
    24
    &gt;&gt;&gt; True.__sizeof__()
    28

What changed in Python 3 that makes the size of `True` greater than the size of `False`?


Content Type	Original Author	Original Content on Stackoverflow
Question	Abhisek	View Question on Stackoverflow
Solution 1 - Python	Bernhard	View Answer on Stackoverflow
Solution 2 - Python	Vinay Sajip	View Answer on Stackoverflow
Solution 3 - Python	jtniehof	View Answer on Stackoverflow

What is python-dev package used for

Python Problem Overview

Python Solutions

Solution 1 - Python

python-dev

lxml

`-dev` packages on Linux

Solution 2 - Python

Solution 3 - Python

How add spaces between Slick carousel item

How to find out the currently logged-in user in Spring Boot?

Attributions

Python Problem Overview

Python Solutions

Solution 1 - Python

python-dev

lxml

-dev packages on Linux

Solution 2 - Python

Solution 3 - Python

How add spaces between Slick carousel item

How to find out the currently logged-in user in Spring Boot?

Attributions

`-dev` packages on Linux