Le 03/01/2012 12:56, Devin Jeanpierre a écrit : >> The second assertion sounds more likely. It seems very odd that Python and >> Perl implementations are divergent on this point. Any opinion ? >> The Python documentation oversimplifies. You meant Perl Documentation, didn't you ? It's a commun opinion that non-capturing groups have a price (minor), for instance Jan Goyvaerts, a well known regular expression guru, refering to Python code, tells : non-capturing groups (...) offer (slightly) better performance as the regex engine doesn't have to keep track of the text matched by non-capturing groups. [link is there : http://stackoverflow.com/questions/2703029/why-regular-expressions-non-capturing-group-is-not-working] It seems Javascript performs better respect to non-capturing groups : http://jsperf.com/regex-capture-vs-non-capture The same for java : http://eyalsch.wordpress.com/2009/05/21/regex/ (no benchmarks). For my part, Python tests didn't show any kind of significative penality.