The state of static analysis on Python

Here is a program that fails with UnboundLocalError three out of four times:

"""Module to demonstrate an error."""

import random

def zero_or_one():
    """Returns either 0 or 1 with equal probability."""
    return random.choice([0, 1])

def main():
    """Function to demonstrate an error."""
    if zero_or_one():
        first = 42
    for _ in range(zero_or_one()):
        second = 42
    print first, second

if __name__ == '__main__':
    main()

Note that line 15 uses the variables first and second, which are defined only if zero_or_one() returned 1 both times.

(Condensed from a real bug where, because of additional indentation, a variable assignment happened as the last line inside a loop, instead of the first line after it.)

I know of three tools that are popular: pychecker, pyflakes, and pylint. None of them say a single thing about this program. It is questionable whether ever (and if so, how often) code like the above is what the programmer intended.

The first of these, pychecker, is not on pip, and requires you to download a file from Sourceforge and run “python setup.py install”. Anyway, this is the output from the three programs:

/tmp% pychecker test.py
Processing module test (test.py)...

Warnings...

None
/tmp% pyflakes test.py
/tmp% pylint test.py
No config file found, using default configuration


Report
======
12 statements analysed.

Statistics by type
------------------

+---------+-------+-----------+-----------+------------+---------+
|type     |number |old number |difference |%documented |%badname |
+=========+=======+===========+===========+============+=========+
|module   |1      |1          |=          |100.00      |0.00     |
+---------+-------+-----------+-----------+------------+---------+
|class    |0      |0          |=          |0           |0        |
+---------+-------+-----------+-----------+------------+---------+
|method   |0      |0          |=          |0           |0        |
+---------+-------+-----------+-----------+------------+---------+
|function |2      |2          |=          |100.00      |0.00     |
+---------+-------+-----------+-----------+------------+---------+



Raw metrics
-----------

+----------+-------+------+---------+-----------+
|type      |number |%     |previous |difference |
+==========+=======+======+=========+===========+
|code      |11     |73.33 |11       |=          |
+----------+-------+------+---------+-----------+
|docstring |3      |20.00 |3        |=          |
+----------+-------+------+---------+-----------+
|comment   |0      |0.00  |0        |=          |
+----------+-------+------+---------+-----------+
|empty     |1      |6.67  |1        |=          |
+----------+-------+------+---------+-----------+



Duplication
-----------

+-------------------------+------+---------+-----------+
|                         |now   |previous |difference |
+=========================+======+=========+===========+
|nb duplicated lines      |0     |0        |=          |
+-------------------------+------+---------+-----------+
|percent duplicated lines |0.000 |0.000    |=          |
+-------------------------+------+---------+-----------+



Messages by category
--------------------

+-----------+-------+---------+-----------+
|type       |number |previous |difference |
+===========+=======+=========+===========+
|convention |0      |0        |=          |
+-----------+-------+---------+-----------+
|refactor   |0      |0        |=          |
+-----------+-------+---------+-----------+
|warning    |0      |0        |=          |
+-----------+-------+---------+-----------+
|error      |0      |0        |=          |
+-----------+-------+---------+-----------+



Global evaluation
-----------------
Your code has been rated at 10.00/10 (previous run: 10.00/10, +0.00)

/tmp% 

Programmer migration

This is common:

and the other direction too:

In general:

Python and Perl:

Now watch:

Sometimes it’s crazy to go back.

Python GUI

From what I can see, the two main contenders are tkinter (ships with the default distribution) and wxPython. The former is easier to learn, has a more “consistent” look, (which basically means it looks terrible everywhere?) and is more suited for quick-and-dirty tasks, etc…

WxPython seems to be the future, has more features, is harder to learn, is more typical of GUItookits, is more actively developed, trickier to install (for users), …

Comparisons here and here.

There is a chooser here.

Update[2007-11-10]: What was was I thinking when I wrote this post? There’s pyGTK and pyQT; why not use one of them? I don’t even know now. Anyway, an old article about toolkits.

[2007-11-20]: Also noticed I had another (private) post that was a link to:
learning python » Blog Archive » Creating a GUI using Python, WxWidgets, and wxPython

That blog also has other posts like this and this, and searching for “pygtk” gives some more posts… Must look at it and learn it sometime.

Random intro-to-python link I’m putting here: Python in a few minutes