How to escape unicode string for regular expressions?

Question

I need to build an re pattern based on the unicode string (e.g. I have "word", and I need something like ^"word"| "word"). However the "word" can contain special re characters. To match the "word" as it is, I need to escape special re characters in unicode string. The basic re.escape() function does the job for ascii strings. How can I do this for unicode?

Answer 1

re.escape() inserts a backslash before every character that's not an ASCII alphanumeric. This may in fact lead to a multitude of unnecessary backslashes to be inserted, however, Python ignores backslashes that don't start a recognized escape sequence, so there is no big harm done (except possibly some performance penalty).

But if you want to build a stricter escape(), you can:

def escape(s):
    return re.sub(r"[(){}\[\].*?|^$\\+-]", r"\\\g<0>", s)

which only touches the actual regex metacharacters. I sure hope I didn't miss any :)