New submission from Jonas H. <[email protected]>:
re.match(p, ...) with a pre-compiled pattern p = re.compile(...) can be much
slower than calling p.match(...). Probably mostly in cases with "easy" patterns
and/or short strings.
The culprit is that re.match -> re._compile can spend a lot of time looking up
p its internal _cache, where it will never find p:
def _compile(pattern, flags):
...
try:
return _cache[type(pattern), pattern, flags]
except KeyError:
pass
if isinstance(pattern, Pattern):
...
return pattern
...
_cache[type(pattern), pattern, flags] = p
...
_compile will always return before the _cache is set if given a Pattern object.
By simply reordering the isinstance(..., Pattern) check we can safe a lot of
time.
I've seen speedups in the range of 2x-5x on some of my data. As an example:
Raw speed of re.compile(p, ...).match():
time ./python.exe -c 'import re'\n'pat = re.compile(".").match'\n'for _ in
range(1_000_000): pat("asdf")'
Executed in 190.59 millis
Speed with this optimization:
time ./python.exe -c 'import re'\n'pat = re.compile(".")'\n'for _ in
range(1_000_000): re.match(pat, "asdf")'
Executed in 291.39 millis
Speed without this optimization:
time ./python.exe -c 'import re'\n'pat = re.compile(".")'\n'for _ in
range(1_000_000): re.match(pat, "asdf")'
Executed in 554.42 millis
----------
components: Regular Expressions
messages: 403851
nosy: ezio.melotti, jonash, mrabarnett
priority: normal
severity: normal
status: open
title: Speed up re.match with pre-compiled patterns
type: performance
versions: Python 3.11
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Python tracker <[email protected]>
<https://bugs.python.org/issue45462>
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