    &gt;&gt;&gt; import struct
    &gt;&gt;&gt; struct.pack(&#39;f&#39;, 3.141592654)
    b&#39;\xdb\x0fI@&#39;
    &gt;&gt;&gt; struct.unpack(&#39;f&#39;, b&#39;\xdb\x0fI@&#39;)
    (3.1415927410125732,)
    &gt;&gt;&gt; struct.pack(&#39;4f&#39;, 1.0, 2.0, 3.0, 4.0)
    &#39;\x00\x00\x80?\x00\x00\x00@\x00\x00@@\x00\x00\x80@&#39;
                          


Just a little addition, if you want a float number as output from the unpack method instead of a tuple just write 

    &gt;&gt;&gt; [x] = struct.unpack(&#39;f&#39;, b&#39;\xdb\x0fI@&#39;)
    &gt;&gt;&gt; x
    3.1415927410125732



If you have more floats then just write

    &gt;&gt;&gt; [x,y] = struct.unpack(&#39;ff&#39;, b&#39;\xdb\x0fI@\x0b\x01I4&#39;)
    &gt;&gt;&gt; x
    3.1415927410125732
    &gt;&gt;&gt; y
    1.8719963179592014e-07
    &gt;&gt;&gt; 



This gets the value of whatever is selected in my dropdown menu.

    document.getElementById(&#39;newSkill&#39;).value

I cannot however find out what property to go after for the text that&#39;s currently displayed by the drop down menu. I tried &quot;text&quot; then looked at [W3Schools][1] but that didn&#39;t have the answer, does anybody here know?

For those not sure, here&#39;s the HTML for a drop down box.

	&lt;select name=&quot;newSkill&quot; id=&quot;newSkill&quot;&gt;
		&lt;option value=&quot;1&quot;&gt;A skill&lt;/option&gt;
		&lt;option value=&quot;2&quot;&gt;Another skill&lt;/option&gt;
		&lt;option value=&quot;3&quot;&gt;Yet another skill&lt;/option&gt;
	&lt;/select&gt;



  [1]: http://w3schools.com/

Getting the text from a drop-down box

I know Python `//` rounds towards negative infinity and in C++ `/` is truncating, rounding towards 0.

And here&#39;s what I know so far:

```lang-none
               |remainder|
-12 / 10  = -1,   - 2      // C++
-12 // 10 = -2,   + 8      # Python

12 / -10  = -1,     2      // C++
12 // -10 = -2,   - 8      # Python

12 / 10  = 1,      2       // Both
12 // 10 = 1,      2

-12 / -10 = 1,    - 2      // Both
          = 2,    + 8

C++:
1. m%(-n) == m%n
2. -m%n == -(m%n)
3. (m/n)*n + m%n == m

Python:
1. m%(-n) == -8 == -(-m%n)
2. (m//n)*n + m%n == m
```

But why Python `//` choose to round towards negative infinity? I didn&#39;t find any resources explain that, but only find and hear people say vaguely: *&quot;for mathematics reasons&quot;*.

For example, in *https://stackoverflow.com/questions/22030342/why-is-1-2-evaluated-to-0-in-c-but-1-in-python*:

&gt; People dealing with these things in the abstract tend to feel that
&gt; rounding toward negative infinity makes more sense (**that means it&#39;s
&gt; compatible with the modulo function as defined in mathematics, rather
&gt; than % having a somewhat funny meaning**).

But I don&#39;t see C++ &#39;s `/` not being compatible with the modulo function. In C++, `(m/n)*n + m%n == m` also applies.

So what&#39;s the (mathematical) reason behind Python choosing rounding towards negative infinity?


----------

See also [Guido van Rossum&#39;s old blog post on the topic][1].

  [1]: http://python-history.blogspot.com/2010/08/why-pythons-integer-division-floors.html









What&#39;s the mathematical reason behind Python choosing to round integer division toward negative infinity?

I have a binary file that I have to parse and I&#39;m using Python. Is there a way to take 4 bytes and convert it to a single precision floating point number?

Convert Bytes to Floating Point Numbers?

<p>I have a binary file that I have to parse and I'm using Python. Is there a way to take 4 bytes and convert it to a single precision floating point number?</p>


When I try to print a Unicode string in a Windows console, I get an error .

`UnicodeEncodeError: &#39;charmap&#39; codec can&#39;t encode character ....`
 
I assume this is because the Windows console does not accept Unicode-only characters. What&#39;s the best way around this? 
Is there any way I can make Python automatically print a `?` instead of failing in this situation?

**Edit:**  I&#39;m using Python 2.5.

----

**Note:** @LasseV.Karlsen answer with the checkmark is sort of outdated (from 2008). Please use the solutions/answers/suggestions below with care!!

[@JFSebastian answer][1] is more relevant as of today (6 Jan 2016).


  [1]: https://stackoverflow.com/a/32176732/610569

Python, Unicode, and the Windows console

I&#39;m downloading an entire directory from a web server. It works OK, but I can&#39;t figure how to get the file size before download to compare if it was updated on the server or not. Can this be done as if I was downloading the file from a FTP server?

    import urllib
    import re

    url = &quot;http://www.someurl.com&quot;

    # Download the page locally
    f = urllib.urlopen(url)
    html = f.read()
    f.close()

    f = open (&quot;temp.htm&quot;, &quot;w&quot;)
    f.write (html)
    f.close()

    # List only the .TXT / .ZIP files
    fnames = re.findall(&#39;^.*&lt;a href=&quot;(\w+(?:\.txt|.zip)?)&quot;.*$&#39;, html, re.MULTILINE)

    for fname in fnames:
        print fname, &quot;...&quot;

        f = urllib.urlopen(url + &quot;/&quot; + fname)

        #### Here I want to check the filesize to download or not #### 
        file = f.read()
        f.close()

        f = open (fname, &quot;w&quot;)
        f.write (file)
        f.close()

---

@Jon: thank for your quick answer. It works, but the filesize on the web server is slightly less than the filesize of the downloaded file. 

Examples:

    Local Size  Server Size
     2.223.533	2.115.516
       664.603	  662.121

It has anything to do with the CR/LF conversion?

Get size of a file before downloading in Python

What are the libraries that support XPath? Is there a full implementation? How is the library used? Where is its website?

How to use XPath in Python?

Is there a maintained package I can use to retrieve and set MP3 ID3 metadata using Python?


Accessing MP3 metadata with Python

Is it possible to write a `doctest` unit test that will check that an exception is raised?  
For example, if I have a function `foo(x)` that is supposed to raise an exception if `x &lt; 0`, how would I write the `doctest` for that? 
 

Can you check that an exception is thrown with doctest in Python?

What would be the most efficient way to compare two `double` or two `float` values?

Simply doing this is not correct:

    bool CompareDoubles1 (double A, double B)
    {
       return A == B;
    }

But something like:

    bool CompareDoubles2 (double A, double B) 
    {
       diff = A - B;
       return (diff &lt; EPSILON) &amp;&amp; (-diff &lt; EPSILON);
    }

Seems to waste processing.

Does anyone know a smarter float comparer?


What is the most effective way for float and double comparison?

The documentation for the [round()][1] function states that you pass it a number, and the positions past the decimal to round. Thus it *should* do this:

    n = 5.59
    round(n, 1) # 5.6

But, in actuality, good old floating point weirdness creeps in and you get:

    5.5999999999999996

For the purposes of UI, I need to display `5.6`. I poked around the Internet and found some [documentation][2] that this is dependent on my implementation of Python. Unfortunately, this occurs on both my Windows dev machine and each Linux server I&#39;ve tried. [See here also][3].

Short of creating my own round library, is there any way around this?



  [1]: http://docs.python.org/lib/built-in-funcs.html
  [2]: http://mail.python.org/pipermail/python-list/2005-September/340383.html
  [3]: http://www.python.org/doc/2.5.1/tut/node16.html

round() doesn&#39;t seem to be rounding properly

I&#39;m writing an application which reads large arrays of floats and performs some simple operations with them. I&#39;m using floats, because I thought it&#39;d be faster than doubles, but after doing some research I&#39;ve found that there&#39;s some confusion about this topic. Can anyone elaborate on this?


Are doubles faster than floats in C#?

How can I round a decimal number (floating point) to the nearest integer? 

e.g.

    1.2 = 1
    1.7 = 2



How do you round a floating point number in Perl?

While working on a project, I came across a JS-script created by a former employee that basically creates a report in the form of

    Name : Value
    Name2 : Value2

etc.

The peoblem is that the values can sometimes be floats (with different precision), integers, or even in the form `2.20011E+17`. What I want to output are pure integers. I don&#39;t know a lot of JavaScript, though.  How would I go about writing a method that takes these sometimes-floats and makes them integers?

Content Type	Original Author	Original Content on Stackoverflow
Question	Cristian	View Question on Stackoverflow
Solution 1 - Python	tzot	View Answer on Stackoverflow
Solution 2 - Python	NDM	View Answer on Stackoverflow

Convert Bytes to Floating Point Numbers?

Python Problem Overview

Python Solutions

Solution 1 - Python

Solution 2 - Python

What's the mathematical reason behind Python choosing to round integer division toward negative infinity?

Getting the text from a drop-down box

Attributions