Python Gotcha's?

[Steven D'Aprano]

On Wed, 04 Apr 2012 15:34:20 -0700, Miki Tebeka wrote:

> Greetings,
> 
> I'm going to give a "Python Gotcha's" talk at work. If you have an
> interesting/common "Gotcha" (warts/dark corners ...) please share.
> 
> (Note that I want over http://wiki.python.org/moin/PythonWarts already).


The GIL prevents Python from taking advantage of multiple cores in your 
CPU when using multiple threads.

Solution: use a GIL-less Python, like IronPython or Jython, or use 
multiple processes instead of threads.



exec() and execfile() are unintuitive if you supply separate dicts for 
the globals and locals arguments.

http://bugs.python.org/issue1167300
http://bugs.python.org/issue14049

Note that both of these are flagged as WON'T FIX.

Solution: to emulate top-level code, pass the same dict as globals and 
locals.


max() and min() fail with a single argument:
    max(2, 3) => 3
    max(3) => raises exception

Solution: don't do that. Or pass a list:
    max([2, 3]) => 3
    max([3]) => 3


Splitting on None and splitting on space is not identical:
    "".split() => []
    "".split(' ') => ['']



JSON expects double-quote marks, not single:
    v = json.loads("{'test':'test'}")  fails
    v = json.loads('{"test":"test"}')  succeeds




If you decorate a function, by default the docstring is lost.

@decorate
def spam(x, y):
    """blah blah blah blah"""

spam.__doc__ => raises exception

Solution: make sure your decorator uses functools.wraps().


-- 
Steven