On 19.05.2017 20:01,
tritium-l...@sdamon.com wrote:
-----Original Message-----
From: Python-ideas [mailto:python-ideas-bounces+tritium-
list=sdamon....@python.org] On Behalf Of Wolfgang Maier
Sent: Friday, May 19, 2017 10:03 AM
To: python-ideas@python.org
Subject: Re: [Python-ideas] fnmatch.filter_false
On 05/17/2017 07:55 PM,
tritium-l...@sdamon.com wrote:
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
If you don't care about slow-downs in this range, you could use this
pattern:
excluded = set(filter(data, '__*'))
result = [item for item in data if item not in excluded]
It seems to take just as much longer although the slow-down is not
constant but depends on the size of the set you need to generate.
Wolfgang
If I didn't care about performance, I wouldn't be using filter - the only
reason to use filter over a list comprehension is performance. The standard
library has a performant inclusion filter, but does not have a performant
exclusion filter.
I'm sorry, but then your statement above doesn't make any sense to me:
"I'm sure there is a better way to do it, and there is a performance
hit, but its negligible."
I'm proposing an alternative to you which times in very similarly to
your own suggestion without copying or modifying stdlib code.
That said I still like your idea of adding the exclude functionality to
fnmatch. I just thought you may be interested in a solution that works
right now.
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