正则表达式将^^和^识别为不同

Question

I am using the Python re module.

I can use the regex r'\\bA\\b' (a raw string) to differentiate between 'A' and 'AA' : it will find a match in the string 'A' and no matches in the string 'AA' .

I would like to achieve the same thing with a carat ^ instead of the A : I want a regex which differentiates between '^' and '^^' .

The problem I have is that the regex r'\\b\\^\\b' does not find a match in '^ '.

Any ideas?

Answer 1

You need to use lookaround for this:

(?<!\^)\^(?!\^)

\\b is a word boundary, a place between a word character and a non-word character, so your pattern is quite non-specific (doesn't say anything about A specifically, A_ would also not match given that _ is a word character.

Here, we assert that there needs to be a place where the preceding character is not a caret, then a caret, then a place where the following character is not a caret (which boils down to "the caret must not be in caret company").