[Python-ideas] Non-boolean return from __contains__

[Jack Diederich]

On Sun, Jul 25, 2010 at 5:20 PM, Bruce Leban <bruce at leapyear.org> wrote:
> Let me see if I understand this:
>
> False in [False]
>
> Returns True now but would return False with your change.

Bigtime.  Official side-effects are neat for hacks but bad for
maintainable code.  You don't know pain until another developer
complains that you refactored user.is_admin() to no longer return the
user's object (for the record that happened in perl, but it could in
python too).  Boolean test operations should return bools for the same
reason that in-place operations should return None.

-Jack