[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 16:40:04 CEST 2012

On Tue, 17 Jul 2012 00🔞55 +1000 Nick Coghlan <ncoghlan at gmail.com> wrote:

Given that all standard library containers default to assuming a size of zero (absent information indicating otherwise), and a special value would need to be special cased by every client of the API (and almost always defaulted to zero), it's simply not a good trade-off.

Actually, dict and set default to a non-zero internal size, but I agree making containers harder to implement is not a good thing.

>> 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.

Noting that infinite iterators are free to define lengthhint to always throw an exception is the status quo.

Being "free" to do unexpected or unconventional things is not the same thing as codifying those behaviours in a PEP, especially when noone is actually doing them. length_hint is supposed to be informative, it shouldn't error out on you. So still -1 from me.

Regards

Antoine.

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