Python 什么是更快的操作，re.match/search 或 str.find？

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

提问by Mike Caron

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

对于一次性字符串搜索，简单地使用 str.find/rfind 是否比使用 re.match/search 更快？

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

也就是说，对于给定的字符串 s，我应该使用：

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

or

或者

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

?

?

采纳答案by user225312

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

问题：使用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:

输出是：

0.441393852234
2.12302494049
0.251421928406

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

因此，您不仅应该使用in运算符，因为它更容易阅读，而且因为它也更快。

回答by Jochen Ritzel

Use this:

用这个：

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.

正则表达式需要先编译，这会增加一些开销。无论如何，Python 的普通字符串搜索非常有效。

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

如果你经常搜索同一个词或者当你做一些更复杂的事情时，正则表达式会变得更有用。

回答by Ben

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

如果您一遍又一遍地搜索相同的东西，re.compile 会大大加快正则表达式的速度。但是我在匹配之前使用“in”来剔除坏情况，从而获得了巨大的加速。轶事，我知道。~本

回答by Yair Beer

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

我遇到了同样的问题。我使用 Jupyter 的 %timeit 来检查：

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 句子中的每个循环 61.3 ns ± 3 ns（平均值 ± 标准差。7 次运行，每次 10000000 次循环）

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

标记列表中的 x 每个循环 93.3 ns ± 1.26 ns（平均值 ± 标准差。7 次运行，每次 10000000 次循环）

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

正则表达式搜索 772 ns ± 8.42 ns 每个循环（平均值 ± 标准偏差。7 次运行，每次 1000000 次循环）

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

编译后的正则表达式搜索每个循环 420 ns ± 7.68 ns（平均值 ± 标准差。7 次运行，每次 1000000 次循环）

Compiling is fast but the simple in is better.

编译速度很快，但简单的更好。

回答by Narann

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

只是为了完成有关正则表达式编译时间的最高投票答案问题，这里有一个带有预编译模式的版本：

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:

还有我的数字：

0.189274072647
0.239935874939
0.0820939540863

回答by PaPeK

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!

也许有人仍然感兴趣。给出的答案看起来不错，但只看一个非常短的字符串。事实上，如果你使用一个长字符串并且你正在寻找的模式大致在最后，那么性能就会改变，有利于正则表达式！

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:

这给出了输出：

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: findand independ on string length and location of pattern in the string while regexis somehow string-length independent and faster for very long strings with the pattern at the end.

总结：find并in依赖于字符串长度和模式在字符串中的位置，而regex对于以模式结尾的非常长的字符串，它在某种程度上与字符串长度无关并且速度更快。