[Python-Dev] Re: string find(substring) vs. substring in string (original) (raw)

Fredrik Lundh fredrik at pythonware.com
Wed Feb 16 22:23:03 CET 2005

Mike Brown wrote:

any special reason why "in" is faster if the substring is found, but a lot slower if it's not in there? Just guessing here, but in general I would think that it would stop searching as soon as it found it, whereas until then, it keeps looking, which takes more time.

the point was that string.find does the same thing, but is much faster in the "no match" case.

But I would also hope that it would be smart enough to know that it doesn't need to look past the 2nd character in 'not the xyz' when it is searching for 'not there' (due to the lengths of the sequences).

note that the target string was "not the xyz"*100, so the search algorithm surely has to look past the second character ;-)

(btw, the benchmark was taken from jim hugunin's ironpython talk, and seems to be carefully designed to kill performance also for more advanced algorithms -- including boyer-moore)

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