[Python-Dev] Do we need length_hint at all? (Was PEP 0424: A method for exposing a length hint) (original) (raw)

Antoine Pitrou solipsis at pitrou.net
Mon Jul 16 16:01:54 CEST 2012

On Mon, 16 Jul 2012 23:23:18 +1000 Nick Coghlan <ncoghlan at gmail.com> wrote:

- distinguishing between different reasons for saying "don't preallocate any space" (i.e. returning zero). I still haven't heard a convincing rationale for this one

The point is that zero is a valid value for a length hint. By making it a special value for "don't know", you are making the protocol potentially confusing, and you are also departing from the current semantics.

(and, yes, I think distinguishing between zero and "don't know" is useful: imagine a container that would preallocate 256 entries by default when the answer is "don't know")

The PEP itself already has this general tone, but I think that it should be even more emphatic that it's about codifying the status quo, not about modifying it with ideas haven't been proven useful through past experience.

Then the PEP shouldn't address infinite iterators at all.

Regards

Antoine.

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