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

Stefan Behnel stefan_ml at behnel.de
Mon Jul 16 11:02:42 CEST 2012

Mark Shannon, 16.07.2012 10:37:
> If resizing of lists is too slow, then we should reconsider the 9/8 factor
> and/or look to tweak the resizing code.

The thing is that the performance is platform specific. On systems with a
fast memory allocator, especially on Linux, the difference is negligible.
However, with a slow memory allocator, especially a slow realloc(), e.g. on
Windows or Solaris, this can substantially hurt the performance, up to a
quadratically increasing runtime in the worst case.

The length hint was implemented specifically to work around this problem.


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