我有一个应用程序代码,可以从配置中动态生成正则表达式以进行一些解析.当两个变化的定时性能时,正被捕获的OR正则表达式的每个部分的正则表达式变化明显慢于正常正则表达式.原因是regex模块内部某些操作的开销.
>>> import timeit
>>> setup = '''
... import re
... '''
#no capture group
>>> print(timeit.timeit("re.search(r'hello|bye|ola|cheers','some say hello,some say bye, or ola or cheers!')", setup=setup))
0.922958850861
#with capture group
>>> print(timeit.timeit("re.search(r'(hello)|(bye)|(ola)|(cheers)','some say hello,some say bye, or ola or cheers!')", setup=setup))
1.44321084023
#no capture group
>>> print(timeit.timeit("re.search(r'hello|bye|ola|cheers','some say hello,some say bye, or ola or cheers!')", setup=setup))
0.913202047348
# capture group
>>> print(timeit.timeit("re.search(r'(hello)|(bye)|(ola)|(cheers)','some say hello,some say bye, or ola or cheers!')", setup=setup))
1.41544604301
问题:使用捕获组时,导致性能大幅下降的原因是什么？