[Python-Dev] 'hasattr' is broken by design

[Glyph Lefkowitz]

On Aug 24, 2010, at 8:31 AM, Benjamin Peterson wrote:

> 2010/8/24 Hrvoje Niksic <hrvoje.niksic at avl.com>:
>> The __length_hint__ lookup expects either no exception or AttributeError,
>> and will propagate others.  I'm not sure if this is a bug.  On the one hand,
>> throwing anything except AttributeError from __getattr__ is bad style (which
>> is why we fixed the bug by deriving our business exception from
>> AttributeError), but the __length_hint__ check is supposed to be an internal
>> optimization completely invisible to the caller of list().
> 
> __length_hint__ is internal and undocumented, so it can do whatever it wants.

As it happens though, list() is _quite_ public.  Saying "X is internal and undocumented, so it can do whatever it wants" is never really realistic, especially in response to someone saying "we already saw this problem in production, _without_ calling / referring to / knowing about this private API".

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