What's a faster operation, re.match/search or str.find?

For one off string searches, is it faster to simply use str.find/rfind than to use re.match/search?

That is, for a given string, s, should I use:

if s.find('lookforme') > -1:
do something

or 

if re.match('lookforme',s):
do something else

?

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小开

Use this:

if 'lookforme' in s:
do something

Regex need to be compiled first, which adds some overhead. Python's normal string search is very efficient anyways.

If you search the same term a lot or when you do something more complex then regex become more useful.

小开
最佳答案

The question: which is faster is best answered by using timeit.

from timeit import timeit
import re


def find(string, text):
if string.find(text) > -1:
pass


def re_find(string, text):
if re.match(text, string):
pass


def best_find(string, text):
if text in string:
pass


print timeit("find(string, text)", "from __main__ import find; string='lookforme'; text='look'")
print timeit("re_find(string, text)", "from __main__ import re_find; string='lookforme'; text='look'")
print timeit("best_find(string, text)", "from __main__ import best_find; string='lookforme'; text='look'")

The output is:

0.441393852234
2.12302494049
0.251421928406

So not only should you use the in operator because it is easier to read, but because it is faster also.

小开

re.compile speeds up regexs a lot if you are searching for the same thing over and over. But I just got a huge speedup by using "in" to cull out bad cases before I match. Anecdotal, I know. ~Ben

小开

I've had the same problem. I used Jupyter's %timeit to check:

import re
sent = "a sentence for measuring a find function"
sent_list = sent.split()
print("x in sentence")
%timeit "function" in sent
print("x in token list")
%timeit "function" in sent_list


print("regex search")
%timeit bool(re.match(".*function.*", sent))
print("compiled regex search")
regex = re.compile(".*function.*")
%timeit bool(regex.match(sent))

x in sentence 61.3 ns ± 3 ns per loop (mean ± std. dev. of 7 runs, 10000000 loops each)

x in token list 93.3 ns ± 1.26 ns per loop (mean ± std. dev. of 7 runs, 10000000 loops each)

regex search 772 ns ± 8.42 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)

compiled regex search 420 ns ± 7.68 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)

Compiling is fast but the simple in is better.

小开

Just to complete the most up-voted answer concerns about regex compilation time, here is a version with precompiled pattern:

from timeit import timeit
import re


def find(string, text):
if string.find(text) > -1:
pass


def re_find(string, text_re):
if text_re.match(string):
pass


def best_find(string, text):
if text in string:
pass


print timeit("find(string, text)", "from __main__ import find; string='lookforme'; text='look'")
print timeit("re_find(string, text_re)", "from __main__ import re_find; string='lookforme'; import re; text_re=re.compile('look')")
print timeit("best_find(string, text)", "from __main__ import best_find; string='lookforme'; text='look'")

And my numbers:

0.189274072647
0.239935874939
0.0820939540863

Precompiled pattern improve numbers, but still, in is the faster.

小开

Maybe someone is still interested. The given answers seem fine but only look at a very short string. In fact if you take a long string and the pattern you are looking for is roughly at the end then the performance changes in favor of regex!

import re


def find(string, text):
if string.find(text) > -1:
pass


def re_find(string, text):
if re.match(text, string):
pass


def best_find(string, text):
if text in string:
pass


very_long_string = 'sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;
ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;
ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd sasgda;dlaskjgasdlj sadlf;jsaf lkjvasdfa dsadkfldsfhsa svnsa;df adsfkj;ljkasdf asdf;lkjafd'
pattern = 'look'
print('pattern at the end of string')
print('find:', end=' ')
%timeit find(very_long_string + pattern, pattern)
print('regex:', end=' ')
%timeit re_find(very_long_string + pattern, pattern)
print('in:', end=' ')
%timeit best_find(very_long_string + pattern, pattern)
print('pattern in front of string')
print('find:', end=' ')
%timeit find(pattern + very_long_string, pattern)
print('regex:', end=' ')
%timeit re_find(pattern + very_long_string, pattern)
print('in:', end=' ')
%timeit best_find(pattern + very_long_string, pattern)

which gives the output:

pattern at the end of string
find: 3.41 µs ± 74.2 ns per loop (mean ± std. dev. of 7 runs, 100000 loops each)
regex: 1.93 µs ± 23.8 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)
in: 3.32 µs ± 74.6 ns per loop (mean ± std. dev. of 7 runs, 100000 loops each)
pattern in front of string
find: 748 ns ± 15.6 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)
regex: 2.03 µs ± 21.1 ns per loop (mean ± std. dev. of 7 runs, 100000 loops each)
in: 589 ns ± 6.75 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)

Summary: find and in depend on string length and location of pattern in the string while regex is somehow string-length independent and faster for very long strings with the pattern at the end.

小开

in addition to above answers, re.search() and re.match() takes the same runtime.

if(re.search(rf"\b{re.escape(some_keyword)}\b",some_sentence))

takes the same runtime as

if(re.search(rf"\b{re.escape(some_keyword)}\b",some_sentence))

and if your regex necessarily require some word match then it is rather a better option to reduce your regex comparison with "if" "in" search. For example the following is faster then then the above two and gives the same result:

if(some_keyword.lower() in some_sentence.lower()):
if(re.search(rf"\b{re.escape(some_keyword)}\b",some_sentence)):

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