[Python-Dev] RE: PySequence_Contains

[Tim Peters]

[Guido]
> ...
> Surely you knew that "x in y" looped over the items of y?  What else
> could it have done?  It was only defined on sequences!

What's a sequence <wink>?  I expect I assumed that enduring a Python method
call for every element of an *instance* was so expensive that Python didn't
bother implementing "in" for instances (just for builtin sequences like lists
and strings etc).  I *know* I assumed it was so expensive that I never tried
it (indeed, I doubt I've used "[not] in" on *any* sort of sequence excepting
"if x in s" where s was a tuple, list or string of length no more than 4; for
anything bigger I always used a dict or bisect).  So it's a personal blind
spot likely due to never looking in that direction.