New submission from Alex Gaynor <alex.gay...@gmail.com>:
This adds a new opcode which for certain list comprehensions (ones with no if
statements and only a single comprehension), preallocates the list to the
appropriate size.
Patch is against 2.7, because it was a bit easier. On:
def f():
for i in range(10000):
[j for j in range(10000)]
f()
Here's the speedup:
alex@alex-gaynor-laptop:/tmp$ # Fresh 2.7 branch
alex@alex-gaynor-laptop:/tmp$ time ~/projects/cpython/python t.py
real 0m6.418s
user 0m6.408s
sys 0m0.004s
alex@alex-gaynor-laptop:/tmp$ time ~/projects/cpython/python t.py
real 0m5.670s
user 0m5.648s
sys 0m0.008s
alex@alex-gaynor-laptop:/tmp$ time ~/projects/cpython/python t.py
real 0m5.688s
user 0m5.672s
sys 0m0.008s
alex@alex-gaynor-laptop:/tmp$ time ~/projects/cpython/python t.py
real 0m5.688s
user 0m5.676s
sys 0m0.004s
alex@alex-gaynor-laptop:/tmp$ time ~/projects/cpython/python t.py
real 0m5.690s
user 0m5.684s
sys 0m0.000s
alex@alex-gaynor-laptop:/tmp$
alex@alex-gaynor-laptop:/tmp$
alex@alex-gaynor-laptop:/tmp$ # With patch
alex@alex-gaynor-laptop:/tmp$ time ~/projects/cpython/python t.py
real 0m6.085s
user 0m6.064s
sys 0m0.008s
alex@alex-gaynor-laptop:/tmp$ time ~/projects/cpython/python t.py
real 0m5.728s
user 0m5.720s
sys 0m0.004s
alex@alex-gaynor-laptop:/tmp$ time ~/projects/cpython/python t.py
real 0m5.783s
user 0m5.772s
sys 0m0.004s
alex@alex-gaynor-laptop:/tmp$ time ~/projects/cpython/python t.py
real 0m4.730s
user 0m4.716s
sys 0m0.008s
alex@alex-gaynor-laptop:/tmp$ time ~/projects/cpython/python t.py
real 0m4.691s
user 0m4.680s
sys 0m0.004s
----------
components: Interpreter Core
files: preallocate.diff
keywords: patch
messages: 154288
nosy: alex
priority: normal
severity: normal
status: open
title: Speed up list comprehensions by preallocating the list where possible
versions: Python 3.4
Added file: http://bugs.python.org/file24642/preallocate.diff
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue14126>
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