Status of PEP's?

[Delaney, Timothy]

> From: Tim Peters [mailto:tim.one at comcast.net]
> [Delaney, Timothy]
> > ...
> > Are the following two equivalent though?
> 
> Not necessarily, but the possible difference isn't where you think:
> 
> > if 1 in obj:
> >     pass
> >
> > if 1 in iter(obj):
> >     pass
> >
> > i.e. is iter(obj) called implicitly in the first case?
> 
> Maybe.  First type(obj) is checked to see whether it 
> implements __contains__
> (at the C level, whether obj->ob_type->tp_as_sequence->sq_contains is
> reachable and non-NULL).  If it is, iter() gets involved if 
> and only if the
> __contains__ method decides to use iter() (and, for example, 
> dicts certainly
> do not).  If type(obj) doesn't implement __contains__, then 
> "in" tickles
> iter(obj) repeatedly.

That's pretty much what I thought - I was assuming the case that
__contains__ wasn't defined. It answers the real question, which was "In the
general case, is '1 in iterable' a valid expression?".

The answer is "Yes, but you can do something to prevent it."

Tim Delaney