re.match / search或str.find是什么更快的操作？

72

对于非字符串搜索，简单地使用str.find / rfind是否比使用re.match / search更快？

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

要么 

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

？

python  performance 
— 迈克·卡伦
source
3
对于一个，我很确定由于额外的开销，正则表达式会更慢。
— Thomas K
1
您应谨慎比较两者，因为它们具有不同的功能。Find搜索整个字符串，而match仅匹配开头（即，它可以提前退出，具体取决于数据）。因此，您要在那里比较苹果和橙子。
— Zoran Pavlovic

Answers:

160

问题：使用最好回答更快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'")

输出为：

0.441393852234
2.12302494049
0.251421928406

因此，不仅应该使用in运算符，因为它更易于阅读，而且因为它也更快。

— 用户名
source
3
最好根据时间选择微优化。但是，+ 1是因为您指定了最
— 容易理解的
5
sukhbir，您当然可以正确回答这个问题。同意，尽管为可读性+1，并且您证明了答案是“ pythonic”答案。
— Mike Caron
4
显然，您是通过叫一个“ best_find”来领导自动陪审团的；-)
— Thomas K
25
众所周知，减慢regexp的主要作用是每次都必须编译模式。如果该模式已预编译并反复使用，则匹配仅比使用find慢25％。
— 贾斯汀·皮尔
4
是re.match()仍然比（连续）慢inS代表了许多可能性的模式？例如a|b|c|d|e|f（预编译模式）。
— Aralox
16

用这个：

if 'lookforme' in s:
    do something

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。

如果您多次搜索相同的术语，或者当您执行更复杂的操作时，则正则表达式将变得更加有用。

— 约臣·里策尔（Jochen Ritzel）
source
4
+1首先是pythonic-然后，如果性能成为问题，请探索不同的实现，看看它们是否可以提高性能。
— Andrew Hare
8

如果您一遍又一遍地搜索同一内容，则re.compile可以大大提高正则表达式的速度。但是通过在比赛之前使用“ in”剔除不良情况，我获得了巨大的提速。轶事，我知道。〜本

— 本
source
6

只是为了完成有关正则表达式编译时间的最受好评的答案，这是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'")

我的电话：

0.189274072647
0.239935874939
0.0820939540863
— 纳兰
source
5

我遇到了同样的问题。我使用Jupyter的％timeit进行了检查：

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))

句子中的x x每循环61.3 ns±3 ns（平均±标准偏差，共运行7次，每个循环10000000次）

令牌列表中的x每个循环93.3 ns±1.26 ns（平均±标准偏差，共运行7次，每个循环10000000次）

正则表达式搜索每个循环772 ns±8.42 ns（平均±标准偏差，共运行7次，每个循环1000000次）

编译的正则表达式搜索每个循环420 ns±7.68 ns（平均±标准偏差，共运行7次，每个循环1000000次）

编译速度很快，但是简单的编译效果更好。

— 耶尔啤酒
source
3

也许有人还是有兴趣的。给定的答案似乎很好，但只看了很短的字符串。实际上，如果您使用了很长的字符串，并且所要查找的模式大约在结尾，那么性能会因使用正则表达式而改变！

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)

它给出了输出：

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)

简介：find并且in取决于字符串长度和模式在字符串中的位置，而regex某种程度上与字符串长度无关，并且对于非常长的带有模式结尾的字符串来说，速度更快。

— 帕佩克
source
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