Python不匹配regexp

Question

>>> pattern = re.compile(r'(.*)\\\\(.*)\\\\(.*)')
>>> m = re.match(pattern, 'string1\string2\string3')
>>> m
>>> 
>>> m.groups
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'NoneType' object has no attribute 'groups'

I am trying to match strings with the following format in the regexp above: string1\\string2\\string3 .

Above is Python's output. Why is it not returning the appropriate regexp object? Is there anything wrong with my pattern?

Answer 1

The issue is that in your pattern, you use \\\\\\\\ , which represents two raw backslashes, while in the text to be matched, you use \\s , which is actually no backslashes at all (it's a \\s character).

First, you probably want to make your text a raw string, otherwise Python reads it as the \\s character.

re.match(pattern, r'string1\string2\string3')

Second, you need only two consecutive slashes in your pattern, to represent that one backslash:

pattern = re.compile(r'(.*)\\(.*)\\(.*)')

Finally, rather than m.groups , you want to do m.groups() (call the method). Thus, all together your code would look like:

pattern = re.compile(r'(.*)\\(.*)\\(.*)')
m = re.match(pattern, r'string1\string2\string3')
m.groups()
# ('string1', 'string2', 'string3')

Answer 2

The problem is that you are trying to escape backslashes inside a raw string. From the Python docs ,

When an 'r' or 'R' prefix is present, a character following a backslash is included in the string without change, and all backslashes are left in the string.

This means that all 8 backslashes stay in your regex, and each pair matches a single backslash in your test string. The problem is immediately apparent when you visualize it (drag the slider above the test string). It can be fixed by replacing your regex with

r'(.*)\\(.*)\\(.*)'