> -----Original Message----- > From: Python-ideas [mailto:python-ideas-bounces+tritium- > list=sdamon....@python.org] On Behalf Of Steven D'Aprano > Sent: Wednesday, May 17, 2017 9:01 PM > To: python-ideas@python.org > Subject: Re: [Python-ideas] fnmatch.filter_false > > On Wed, May 17, 2017 at 12:14:05PM -0400, Alex Walters wrote: > > Fnmath.filter works great. To remind people what it does, it takes an > > iterable of strings and a pattern and returns a list of the strings that > > match the pattern. And that is wonderful > > > > However, I often need to filter *out* the items that match the pattern (to > > ignore them). In every project that I need this I end up copying the > > function out of the fnmatch library and adding 'not' to the test clause. > > At the cost of a slight inefficiency, you could use the pure Python > equivalent given in the docs: > > https://docs.python.org/3/library/fnmatch.html#fnmatch.filter > > > fnmatch.filter(names, pattern) > > Return the subset of the list of names that match pattern. It is > the same as [n for n in names if fnmatch(n, pattern)], but implemented > more efficiently. > > So your filter_false is: > > [n for n in names if not fnmatch(n, pattern)] > > which avoids the need for the copy-and-paste anti-pattern.
I ran a test on the same dataset using listcomps. The modified version of filter is still 22.<some noise>, the unmodified version is still 19.<some noise>. However the listcomp method is 41.<some noise>. That performance is important, at least to me. Before you ask, yes, I have profiled my code, and filtering is a bottleneck. > > Otherwise, I would support: > > - filter_false > > - or a glob symbol to reverse the sense of the test, e.g. ~ or ! > as the first character; > > > but I dislike functions that take boolean arguments to change their > behaviour. It's not a 100% hard and fast rule, but in general I prefer > to avoid functions that take a constant bool argument: > > # rather than this: > function(important_args, True) > function(important_args, False) > > # use this: > function(important_args) > function_false(important_args) > > (although there may be exceptions). > That is a fair enough argument. In moderate defense of the code I posted earlier, I did make the inversion variable keyword only. > > -- > Steve > _______________________________________________ > Python-ideas mailing list > Python-ideas@python.org > https://mail.python.org/mailman/listinfo/python-ideas > Code of Conduct: http://python.org/psf/codeofconduct/ _______________________________________________ Python-ideas mailing list Python-ideas@python.org https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/
