python - 在考虑带有撇号的单词时，如何在 python 中使用正则表达式分隔单词？

Question

我尝试使用单词边界在 python 正则表达式中分离 m，并找到它们。这些 m 应该在两边都有一个空格或开始/结束字符串:

r = re.compile("\\bm\\b")
re.findall(r, someString)

但是，由于撇号被认为是单词边界，因此此方法还可以在 I'm 等单词中找到 m。如何编写不将撇号视为单词边界的正则表达式？

我已经试过了:

r = re.compile("(\\sm\\s) | (^m) | (m$)")
re.findall(r, someString)

但这与任何 m 都不匹配。奇怪。

Answer 1

使用环视断言:

>>> import re
>>> re.findall(r'(?<=\s)m(?=\s)|^m|m$', "I'm a boy")
[]
>>> re.findall(r'(?<=\s)m(?=\s)|^m|m$', "I m a boy")
['m']
>>> re.findall(r'(?<=\s)m(?=\s)|^m|m$', "mama")
['m']
>>> re.findall(r'(?<=\s)m(?=\s)|^m|m$', "pm")
['m']

(?=...)

Matches if ... matches next, but doesn’t consume any of the string. This is called a lookahead assertion. For example, Isaac (?=Asimov) will match 'Isaac ' only if it’s followed by 'Asimov'.

(?<=...)

Matches if the current position in the string is preceded by a match for ... that ends at the current position. This is called a positive lookbehind assertion. (?<=abc)def will find a match in abcdef, ...

from Regular expression syntax

顺便说一句，使用原始字符串( r'this is raw string' )，您不需要转义 \ .

>>> r'\s' == '\\s'
True