One reason is that `dict.keys()` predates the introduction of sets into the language.

Note that the return type of `dict.keys()` has changed in Python 3: the function now returns a &quot;set-like&quot; [view][1] rather than a list.

&gt; For set-like views, all of the operations defined for the abstract base class `collections.abc.Set` are available (for example, `==`, `&lt;`, or `^`).

  [1]: http://docs.python.org/3.8/library/stdtypes.html#dict-views

In python 2, it&#39;s less efficient to construct a set than a list.

Don&#39;t want to make an assumption that the user of the return value will want to search within the result.   Iteration is also likely.   

In python 3, it&#39;s no longer a list.   It&#39;s an ordered iterable because ordering is guaranteed.

I was getting the below message from Visual Studio 2010.

&gt;&quot;This project is incompatible with the current version of Visual Studio&quot; 

One situation resulting in this error has already been posted here at Stackoverflow, but [that question][1] has been closed. I&#39;m thinking it&#39;s a fairly generic problem. Since I have found a &quot;solution&quot;, I&#39;ll post this question, and my solution as an answer. 


  [1]: https://stackoverflow.com/questions/12782863/the-error-this-project-is-incompatible-with-the-current-version-of-visual-studi

&quot;This project is incompatible with the current version of Visual Studio&quot;

How would you create a qq-plot using Python?

Assuming that you have a large set of measurements and are using some plotting function that takes XY-values as input. The function should plot the quantiles of the measurements against the corresponding quantiles of some distribution (normal, uniform...).

The resulting plot lets us then evaluate in our measurement follows the assumed distribution or not.

http://en.wikipedia.org/wiki/Quantile-quantile_plot

Both R and Matlab provide ready made functions for this, but I am wondering what the cleanest method for implementing in in Python would be.

Quantile-Quantile Plot using SciPy

I would&#39;ve expected Python&#39;s keys method to return a set instead of a list.  Since it most closely resembles the kind of guarantees that keys of a hashmap would give.  Specifically, they are unique and not sorted, like a set.  However, this method returns a list:

    &gt;&gt;&gt; d = {}
    &gt;&gt;&gt; d.keys().__class__
    &lt;type &#39;list&#39;&gt;

Is this just a mistake in the Python API or is there some other reason I am missing?


Why does Python&#39;s dict.keys() return a list and not a set?

I would've expected Python's keys method to return a set instead of a list. Since it most closely resembles the kind of guarantees that keys of a hashmap would give. Specifically, they are unique and not sorted, like a set. However, this method returns a list:
<pre><code class="hljs language-python">>>> d = {}
>>> d.keys().__class__
&#x3C;type 'list'>
</code></pre>
Is this just a mistake in the Python API or is there some other reason I am missing?

I am in the process of learning Python and I have reached the section about the `pass` statement. The guide I&#39;m using defines it as being a null statement that is commonly used as a placeholder. 

I still don&#39;t fully understand what that means though. What would be a simple/basic situation where the `pass` statement would be used and why would it be needed?


How to use the pass statement

I know that I can get the unique values of a `DataFrame` by resetting the index but is there a way to avoid this step and get the unique values directly?

Given I have:

            C
     A B     
     0 one  3
     1 one  2
     2 two  1

I can do:
 
    df = df.reset_index()
    uniq_b = df.B.unique()
    df = df.set_index([&#39;A&#39;,&#39;B&#39;])

Is there a way built in pandas to do this?

Get unique values from index column in MultiIndex

Does `time.time()` in the Python time module return the system&#39;s time or the time in UTC?

Does Python&#39;s time.time() return the local or UTC timestamp?

I want to append characters to a string, but want to make sure all the letters in the final list are **unique**.

Example: `&quot;aaabcabccd&quot;` → `&quot;abcd&quot;`

Now of course I have two solutions in my mind. One is using a `list` that will map the characters with their ASCII codes. So whenever I encounter a letter it will set the index to `True`. Afterwards I will scan the list and append all the ones that were set. It will have a time complexity of **O(n)**.

Another solution would be using a `dict` and following the same procedure. After mapping every char, I will do the operation for each key in the dictionary. This will have a **linear** running time as well.

Since I am a Python newbie, I was wondering which would be more space efficient. Which one could be implemented more efficiently?

**PS**: Order is ***not*** important while creating the list.

List of all unique characters in a string?

How do you access other class variables from a list comprehension within the class definition?  The following works in Python 2 but fails in Python 3:

    class Foo:
        x = 5
        y = [x for i in range(1)]

Python 3.2 gives the error:

    NameError: global name &#39;x&#39; is not defined

Trying `Foo.x` doesn&#39;t work either.  Any ideas on how to do this in Python 3?

A slightly more complicated motivating example:

    from collections import namedtuple
    class StateDatabase:
        State = namedtuple(&#39;State&#39;, [&#39;name&#39;, &#39;capital&#39;])
        db = [State(*args) for args in [
            [&#39;Alabama&#39;, &#39;Montgomery&#39;],
            [&#39;Alaska&#39;, &#39;Juneau&#39;],
            # ...
        ]]

In this example, `apply()` would have been a decent workaround, but it is sadly removed from Python 3.

Accessing class variables from a list comprehension in the class definition

I have found documentation about subprocess.check_output() but I cannot find one with  arguments and the documentation is not very in depth. I am using Python 3 (but am trying to run a Python 2 file through Python 3)

I am trying to run this command:
`python py2.py -i test.txt`

-i is a positional argument for argparse, test.txt is what the -i is, py2.py is the file to run

I have tried a lot of (non working) variations including:
`py2output = subprocess.check_output([str(&#39;python py2.py &#39;),&#39;-i&#39;, &#39;test.txt&#39;])`

`py2output = subprocess.check_output([str(&#39;python&#39;),&#39;py2.py&#39;,&#39;-i&#39;, test.txt&#39;])`



How do you use subprocess.check_output() in Python?

I&#39;m trying to read in a string representation of a Tuple from a file, and add the tuple to a list. Here&#39;s the relevant code.

    raw_data = userfile.read().split(&#39;\n&#39;)
    for a in raw_data : 
        print a
        btc_history.append(ast.literal_eval(a))

Here is the output:

    (Decimal(&#39;11.66985&#39;), Decimal(&#39;0E-8&#39;))
    Traceback (most recent call last):
  

    File &quot;./goxnotify.py&quot;, line 74, in &lt;module&gt;
        main()
      File &quot;./goxnotify.py&quot;, line 68, in main
        local.load_user_file(username,btc_history)
      File &quot;/home/unix-dude/Code/GoxNotify/local_functions.py&quot;, line 53, in load_user_file
        btc_history.append(ast.literal_eval(a))
      File &quot;/usr/lib/python2.7/ast.py&quot;, line 80, in literal_eval
        return _convert(node_or_string)

      `File &quot;/usr/lib/python2.7/ast.py&quot;, line 58, in _convert
       return tuple(map(_convert, node.elts))
      File &quot;/usr/lib/python2.7/ast.py&quot;, line 79, in _convert
       raise ValueError(&#39;malformed string&#39;)
       ValueError: malformed string


Malformed String ValueError ast.literal_eval() with String representation of Tuple

when I do curl to a API call link http://example.com/passkey=wedsmdjsjmdd

    curl &#39;http://example.com/passkey=wedsmdjsjmdd&#39;

I get the employee output data on a csv file format, like:


    &quot;Steve&quot;,&quot;421&quot;,&quot;0&quot;,&quot;421&quot;,&quot;2&quot;,&quot;&quot;,&quot;&quot;,&quot;&quot;,&quot;&quot;,&quot;&quot;,&quot;&quot;,&quot;&quot;,&quot;&quot;,&quot;421&quot;,&quot;0&quot;,&quot;421&quot;,&quot;2&quot;

how can parse through this using python.

I tried:

    import csv 
    cr = csv.reader(open(&#39;http://example.com/passkey=wedsmdjsjmdd&#39;,&quot;rb&quot;))
    for row in cr:
        print row


but it didn&#39;t work and I got an error

`http://example.com/passkey=wedsmdjsjmdd No such file or directory:`


Thanks!

How to read a CSV file from a URL with Python?

Is there a standard way of using exception chains in Python?  Like the Java exception &#39;caused by&#39;?

Here is some background.

I have a module with one main exception class `DSError`:

     class DSError(Exception):
         pass

Somewhere within this module there will be:

    try:
        v = my_dict[k]
        something(v)
    except KeyError as e:
        raise DSError(&quot;no key %s found for %s&quot; % (k, self))
    except ValueError as e:
        raise DSError(&quot;Bad Value %s found for %s&quot; % (v, self))
    except DSError as e:
        raise DSError(&quot;%s raised in %s&quot; % (e, self))

Basically this snippet should throw only DSError and tell me what happened and why.  The thing is that the try block might throw lots of other exceptions, so I&#39;d prefer if I can do something like:

    try:
        v = my_dict[k]
        something(v)
    except Exception as e:
        raise DSError(self, v, e)  # Exception chained...

Is this standard pythonic way?  I did not see exception chains in other modules so how is that done in Python?


Python exception chaining

In my project, I have a bunch of strings that are read in from a file. Most of them, when printed in the command console, exceed 80 characters in length and wrap around, looking ugly.

I want to be able to have Python read the string, then test if it is over 75 characters in length. If it is, then split the string up into multiple strings, then print one after the other on a new line.
I also want it to be smart, not cutting off full words. i.e. `&quot;The quick brown &lt;newline&gt; fox...&quot;` instead of `&quot;the quick bro&lt;newline&gt;wn fox...&quot;`.

I&#39;ve tried modifying similar code that truncates the string after a set length, but just trashes the string instead of putting it in a new line.

What are some methods I could use to accomplish this?

Content Type	Original Author	Original Content on Stackoverflow
Question	oneself	View Question on Stackoverflow
Solution 1 - Python	NPE	View Answer on Stackoverflow
Solution 2 - Python	Erik Aronesty	View Answer on Stackoverflow

Why does Python's dict.keys() return a list and not a set?

Python Problem Overview

Python Solutions

Solution 1 - Python

Solution 2 - Python

Quantile-Quantile Plot using SciPy

"This project is incompatible with the current version of Visual Studio"

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