Python Programming Language :: Is 1 large Regex faster than 3 smaller ones?


	Is 1 large Regex faster than 3 smaller ones? Hi, I need to match 3 small strings in a small text file (about 200 words of text). Would it be faster to write 1 compiled regex that matches all 3 substrings in one go, or to use 3 separate regular expressions to do the same job? Thanks! Erik In article <1180896727.419817.303@p47g2000hsd.googlegroups.com>, erikcw <erikwickst@gmail.com> wrote: > Hi, > I need to match 3 small strings in a small text file (about 200 words > of text). > Would it be faster to write 1 compiled regex that matches all 3 > substrings in one go, or to use 3 separate regular expressions to do > the same job? > Thanks! > Erik For a classic regex, the answer is one big one. Matching against a regex takes time proportional to the number of characters of input. One big regex will probably consume more memory, and may be slower to compile, but it should run faster. On the other hand, there are a lot of things that pattern maching libraries accept these days under the guise of being a "regex" which are not strictly regexes in the classic sense. From a purely practical point of view, if your input is only 200 words, it's likely that the search time will be insignificant no matter what you do. On Jun 4, 4:52 am, erikcw <erikwickst@gmail.com> wrote: > Hi, > I need to match 3 small strings in a small text file (about 200 words > of text). > Would it be faster to write 1 compiled regex that matches all 3 > substrings in one go, or to use 3 separate regular expressions to do > the same job? Taking your question literally: we have no idea how long it might take you to write alternative versions of source code. Guessing that you mean "Which would run faster?": both should run over a 200-word text file in imperceptibly different time (unless of course you make a mistake), and the time should be tiny compared to the time required to open the file (again unless of course you make a mistake). I'd suggest that as a learning exercise you do both, check the accuracy of both (text e.g. matching only 2 out of 3, sought strings in different orders, etc), and then and only then worry about the time it takes. HTH, John