[issue33234] Improve list() pre-sizing for inputs with known lengths

[Serhiy Storchaka]

Serhiy Storchaka <storchaka+cpython at gmail.com> added the comment:

Calling PyObject_LengthHint() adds an overhead. It is significant for short sequences. I work on a patch that reduces it. PR 6493 adds the second call of PyObject_LengthHint() and increases the overhead.

As for this issue, in-place repeat overallocates too.

>>> a = [0]; a *= 10; getsizeof(a)
200

I think it would be better to make it not preallocating.

And maybe it would be worth to avoid overallocating if newsize > allocated + allocated/8 or something like.

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nosy: +serhiy.storchaka

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<https://bugs.python.org/issue33234>
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