Question

我有

的字符串输入

s = 'horse dog cat bear'

我希望将单词的顺序更改为

cat horse dog bear

相应的re将是

>>> import re
>>> s = 'horse dog cat bear'
>>> print re.sub(r'(horse )(dog )?(cat )(bear)', r'\3\1\2\4', s)
cat horse dog bear

我使用了(dog )?，因为当dog不存在时我还想匹配字符串。因此输出应为cat horse bear。但是当我尝试时，我遇到了以下错误 -

>>> s = 'horse cat bear'
>>> print re.sub(r'(horse )(dog )?(cat )(bear)', r'\3\1\2\4', s)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.7/re.py", line 155, in sub
    return _compile(pattern, flags).sub(repl, string, count)
  File "/usr/lib/python2.7/re.py", line 291, in filter
    return sre_parse.expand_template(template, match)
  File "/usr/lib/python2.7/sre_parse.py", line 831, in expand_template
    raise error, "unmatched group"
sre_constants.error: unmatched group
>>>

即使dog不存在，我怎样才能获得输出？

Answer 1

尝试

r'(horse )((?:dog )?)(cat )(bear)'

即。使捕获组的内容可选，而不是组本身。

Answer 2

您需要使用re吗？你可以用列表来做。

s0 = 'horse dog cat bear'
s1 = 'horse cat bear'
s_map = 'cat horse dog bear'.split()

print(" ".join([x for x in s_map if x in s0.split()]))
print(" ".join([x for x in s_map if x in s1.split()]))

输出：

cat horse dog bear
cat horse bear

如何在re python中忽略字符串中不匹配的组？

2 个答案: