[issue26828] Implement __length_hint__() on map() and filter() to optimize list(map) and list(filter)

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

See also issue14126.

It makes sense to implement map.__length_hint__() and  zip.__length_hint__(). But note that map() and zip() take several iterables, and we should call __length_hint__() for every of them (unless found a one with not implemented __length_hint__()). This can slow down the execution for short sequences.

It is impossible to implement reasonable filter.__length_hint__(), because the length of resulting sequence can be from 0 to the length of the input sequence, and returning the maximal value would be not correct.

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nosy: +rhettinger

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue26828>
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