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Author alex
Recipients alex
Date 2012-02-25.23:29:25
SpamBayes Score 0.0018941681
Marked as misclassified No
Message-id <1330212567.11.0.0699848649478.issue14126@psf.upfronthosting.co.za>
In-reply-to
Content 
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
History
Date User Action Args
2012-02-25 23:29:27alexsetrecipients: + alex
2012-02-25 23:29:27alexsetmessageid: <1330212567.11.0.0699848649478.issue14126@psf.upfronthosting.co.za>
2012-02-25 23:29:26alexlinkissue14126 messages
2012-02-25 23:29:26alexcreate