[Python-ideas] fnmatch.filter_false

[tritium-list at sdamon.com]

Top posting, apologies.

I'm sure there is a better way to do it, and there is a performance hit, but
its negligible.  This is also a three line delta of the function.

from fnmatch import _compile_pattern, filter as old_filter
import os
import os.path
import posixpath


data = os.listdir()

def filter(names, pat, *, invert=False):
    """Return the subset of the list NAMES that match PAT."""
    result = []
    pat = os.path.normcase(pat)
    match = _compile_pattern(pat)
    if os.path is posixpath:
        # normcase on posix is NOP. Optimize it away from the loop.
        for name in names:
            if bool(match(name)) == (not invert):
                result.append(name)
    else:
        for name in names:
            if bool(match(os.path.normcase(name))) == (not invert):
                result.append(name)
    return result

if __name__ == '__main__':
    import timeit
    print(timeit.timeit(
        "filter(data, '__*')",
        setup="from __main__ import filter, data"
     ))
    print(timeit.timeit(
        "filter(data, '__*')",
        setup="from __main__ import old_filter as filter, data"
    ))

The first test (modified code) timed at 22.492161903402575, where the second
test (unmodified) timed at 19.555531892032324



> -----Original Message-----
> From: tritium-list at sdamon.com [mailto:tritium-list at sdamon.com]
> Sent: Wednesday, May 17, 2017 1:19 PM
> To: python-ideas at python.org
> Subject: RE: [Python-ideas] fnmatch.filter_false
> 
> > -----Original Message-----
> > From: Python-ideas [mailto:python-ideas-bounces+tritium-
> > list=sdamon.com at python.org] On Behalf Of Oleg Broytman
> > Sent: Wednesday, May 17, 2017 12:44 PM
> > To: python-ideas at python.org
> > Subject: Re: [Python-ideas] fnmatch.filter_false
> >
> > On Wed, May 17, 2017 at 12:14:05PM -0400, Alex Walters <tritium-
> > list at sdamon.com> 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.
> It
> > > would be wonderful if there was a filter_false version in the standard
> > > library.  Or in inversion Boolean option.  Or something, to stop from
> having
> > > to copy code every time I need to ignore files.
> >
> >    Why not create a package and publish at PyPI? Then all you need is
> > pip install fnmatch_filter_false
> >    in your virtual env.
> 
> That is my normal thought on something like this, but in the case of
adding
> a Boolean argument to fnmatch.filter, it (might be) as simple as a 3 line
> diff that does not break the API, and as far as I can tell, does not have
> performance implications.  Copying a module out of the standard library
that
> is identical except a 3 line diff that does not break compatibility with
the
> standard library... that just wreaks of something that should be in the
> standard library to begin with.
> 
> In the case of adding a separate function to fnmatch, it's still not that
> big of a diff, and wouldn't have much duplicated code, at least in the way
I
> would implement it - it would essentially do the previous Boolean option
> method, and wrap that.  A filter_false function, now that I think about
it,
> is less ideal than just adding a keyword only Boolean option to
> fnmatch.filter.
> 
> > Oleg.
> > --
> >      Oleg Broytman            http://phdru.name/
phd at phdru.name
> >            Programmers don't die, they just GOSUB without RETURN.
> > _______________________________________________
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