It's not quite that simple -- those containers use the hash to find the objects that will be first checked by identity, and then equality* -- otherwise they would have to do a complete scan from first key to last, and that would kill performance.

...

Okay, I see your point -- even for sane objects, a systematic check of every key is not undertaken for the hash-type containers.

Perhaps something like:

For container types such as list, tuple, or collections.deque, the expression 'x in y' is equivalent to 'any(x is e or x == e for e in y)'.  For container types such as set, frozenset, and dict, 'x in y' is equivalent to 'any(x is e or x == e for e in z)' where 'z' is a collection of objects in 'y' that have the same hash.