[PATCH 2 of 4] Do not use str.startswith or str.endswith to find a single character

[Benoit Boissinot]

On Sun, Aug 23, 2009 at 03:21:00PM +0200, Nicolas Dumazet wrote:
> 2009/8/23 Benoit Boissinot <benoit.boissinot at ens-lyon.org>:
> > On Sat, Aug 22, 2009 at 08:39:43PM +0200, Nicolas Dumazet wrote:
> >> # HG changeset patch
> >> # User Nicolas Dumazet <nicdumz.commits at gmail.com>
> >> # Date 1250960622 -7200
> >> # Node ID 51f0751ed3681aee75842e2351445ff30054062b
> >> # Parent  f7a1dd3fa57b6be41c0c5535a16531b710571bb7
> >> Do not use str.startswith or str.endswith to find a single character
> >>
> >> When startswith (resp. endswith) is called on a single character, it is two times
> >> faster to directly compare that single character with str[0] (resp. str[-1]).
> >>
> >> * str.startswith(char) -> (str and) str[0] == char
> >> * str.endswith(char) -> (str and) str[-1] == char
> >
> > I don't really like this one, I think it hurts the readability. Did you
> > check the python source to understand the issue (and does your benchmark
> > include the time to test if the string is not empty?) ?
> 
> That's what I think too, it does hurt readability when we have to
> include non-emptiness tests. But when we know that the string can't be
> empty, I think that readability of s[0] == 'a' is equivalent to
> s.startswith('a').
> 
> In terms of C, we are comparing (string conversions, size comparisons
> and a memcmp) vs (a pointer access and a single-character-string
> creation, knowing that characters/single-letter strings are cached in
> CPython).

You could use s[:1], it's still the exact thing and it's as fast as
s[0].


Benoit
-- 
:wq