[New-bugs-announce] [issue37435] builtin map iterator should provide __length_hint__

[Nicholas Musolino]

New submission from Nicholas Musolino <n.musolino at gmail.com>:

The builtin `map` function takes one or more user-supplied iterators, and returns an iterator.

When all the user-supplied iterator arguments to `map` provide a valid length hint (according to the PEP 424 length hint protocol), the iterator returned by `map` should provide a length hint.  

I suggest the following behavior:  when all the iterator arguments provide a valid length hint, the map iterator should return the minimum value among all length hint values, because it stops upon exhaustion of the shortest input iterator.

If any user-supplied iterator does *not* provide a length hint according to the PEP 424 protocol, the map iterator should return the `NotImplemented` singleton, in accordance with the protocol.

When the evaluation of `__length_hint__()` for a user-supplied iterator raises an exception, the exception should be propagated by the map iterator's `__length_hint__()` method.

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components: Interpreter Core
messages: 346772
nosy: nmusolino
priority: normal
severity: normal
status: open
title: builtin map iterator should provide __length_hint__
type: enhancement

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue37435>
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