[Python-Dev] PEP 0424: A method for exposing a length hint (original) (raw)

Stefan Behnel stefan_ml at behnel.de
Mon Jul 16 08:54:27 CEST 2012

Mark Shannon, 15.07.2012 16:14:

Alex Gaynor wrote:

CPython currently defines an _lengthhint_ method on several types, such as various iterators. This method is then used by various other functions (such as map) to presize lists based on the estimated returned by Don't use "map" as an example. map returns an iterator so it doesn't need lengthhint

Right. It's a good example for something else, though. As I mentioned before, iterators should be able to propagate the length hint of an underlying iterator, e.g. in generator expressions or map(). I consider that an important feature that the protocol must support.

Stefan

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