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Possible bug with stability of mimetypes.guess_* function output

Johannes Bauer dfnsonfsduifb at gmx.de
Fri Feb 7 13:06:36 EST 2014 
Hi group,

I'm using Python 3.3.2+ (default, Oct  9 2013, 14:50:09) [GCC 4.8.1] on
linux and have found what is very peculiar behavior at best and a bug at
worst. It regards the mimetypes module and in particular the
guess_all_extensions and guess_extension functions.

I've found that these do not return stable output. When running the
following commands, it returns one of:

$ python3 -c 'import mimetypes;
print(mimetypes.guess_all_extensions("text/html"),
mimetypes.guess_extension("text/html"))'
['.htm', '.html', '.shtml'] .htm

$ python3 -c 'import mimetypes;
print(mimetypes.guess_all_extensions("text/html"),
mimetypes.guess_extension("text/html"))'
['.html', '.htm', '.shtml'] .html

So guess_extension(x) seems to always return guess_all_extensions(x)[0].

Curiously, "shtml" is never the first element. The other two are mixed
with a probability of around 50% which leads me to believe they're
internally managed as a set and are therefore affected by the
(relatively new) nondeterministic hashing function initialization.

I don't know if stable output is guaranteed for these functions, but it
sure would be nice. Messes up a whole bunch of things otherwise :-/

Please let me know if this is a bug or expected behavior.
Best regards,
Johannes

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