Django is always using Python 2.3 fallback methods

[Chris Beaven]

Throughout Django, the following way is used to fall back import the Python 2.3 methods if the Python 2.4+ builtin methods set and reversed do not exist:

if hasattr(__builtins__, 'set'):
    ...

But Django is converting __builtins__ to a dict somehow, when it's usually a module (try >>> type(__builtins__) from a manage.py shell then from a normal Python shell), and a dict doesn't have the attribute set (or reversed).

[Chris Beaven]

Thanks to the IRC team, I have a bit more of an understanding now.

​`__builtins__` can either be a module or dict -- we shouldn't be relying on it being a module. Instead we should be doing:

import __builtin__
if hasattr(__builtin__, 'set'):
    ...

[anonymous]

For clarity; it appears to be not Django that makes Python modify __builtins__ to a dict, but code.py used for the standard python interactive prompt.

People using IPython are having a module and not a Dict for __builtins__, still if Python can arbitrarily change the definition of builtins from a module to a Dict depending on circumstances it makes sense to code this in a way that is not prone to arbitrary definitions. As the linked email suggests.

[Chris Beaven]

Patch standardizes all use of this method (and does it for the contrib.auth module which was only using the old 2.3 set method)

[James Bennett]

Out of curiosity, wouldn't this be cleaner:

try:
    set
except NameError:
    from sets import Set as set

[Adrian Holovaty]

Yeah, ubuernostrum's suggestion seems more elegant. Any downsides to that?

[Malcolm Tredinnick]

(In [5514]) Fixed #4607 -- Tweaked checks for features missing in Python 2.3 to not assume
things Python does not guarantee. Patch from SmileyChris.