如何使用Python的regex匹配下划线？

Question

我在使用正则表达式匹配Python中的下划线字符时遇到问题。只是在弹壳里玩，我得到：

>>> import re
>>> re.match(r'a', 'abc')
<_sre.SRE_Match object at 0xb746a368>
>>> re.match(r'_', 'ab_c')
>>> re.match(r'[_]', 'ab_c')
>>> re.match(r'\_', 'ab_c')

我希望至少有一个返回匹配对象。我做错什么了吗？

Answer 1

请尝试以下操作：

re.search(r'\_', 'ab_c')

你转义下划线字符是对的！ 请注意，您只能对字符串的开头使用match，这在文档（https://docs.python.org/2/library/re.html）中也很清楚：

If zero or more characters at the beginning of string match the regular expression pattern, return a corresponding MatchObject instance. Return None if the string does not match the pattern; note that this is different from a zero-length match.

在这种情况下，应该使用search：

Scan through string looking for the first location where the regular expression pattern produces a match, and return a corresponding MatchObject instance. Return None if no position in the string matches the pattern; note that this is different from finding a zero-length match at some point in the string.

Answer 2

如果您要查找的模式不在搜索字符串的开头，请使用re.search，而不是re.match。

re.match(pattern, string, flags=0)

Try to apply the pattern at the start of the string, returning a match object, or None if no match was found.

re.search(pattern, string, flags=0)

Scan through string looking for a match to the pattern, returning a match object, or None if no match was found.

您不需要转义_，甚至不需要使用原始字符串。

>>> re.search('_', 'ab_c')
Out[4]: <_sre.SRE_Match object; span=(2, 3), match='_'>