Tim Peters <t...@python.org> added the comment:
Yes, it's quadratic time. If the string being searched has N characters, first it fails to find "x" in all N of 'em, then `.*` advances by one and it fails to find "x" in the trailing N-1 characters, then again in the trailing N-2, and so on. N + N-1 + N-2 + ... + 1 is quadratic in N. That's how this kind of regexp engine works. And it's mild, as such things go: you can also create poor regexps that take time _exponential_ in N that fail to match certain strings. It's unlikely this will change without replacing Python's regexp implementation entirely. For why, see Jeffrey Friedl's book "Mastering Regular Expressions" (published by O'Reilly). That book also spells out techniques for crafting regexps that don't suck ;-) It's not a small topic, alas. ---------- nosy: +tim.peters _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue35915> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
