Python Regex: escaping a back-reference

Question

Here is my situation:

re.sub(r'([^\\])', r'\1[\W\1]*', string)

It is straight forward that I want to append [\\W(itself)] after (itself) for itself being a group of characters (can be special). That is why I need to put it in a set to strip away all special meanings. However, my group can be a SET. I know that nested sets do not work. How do I escape / remove the square brackets to safely put my group in the set?

My other attempt was to use \\1(\\W|\\1)* instead, but I need to escape characters in my group without escaping possible square brackets in the group. How do I do so?

This is a dilemma. I do not know how to solve this problem and which way to go. Please help.

Thank you very much.

EDIT: I skipped a step. After matching a character but \\ (the [^\\] part) and replace with the explained expression, I will sometime need to replace it with a set of similar characters. So, 'a' becomes '[a@]', 's' becomes '[s5$]', etc... The question was really wrong. But I solved the problem, so if you are still trying to make some sense out of what I wrote earlier, please don't :)

Answer 1

You can use a function as the replacement in re.sub . This will allow you to call re.escape on your match before performing the substitution:

def escape_repl(match):
    return '{0}[\W{0}]*'.format(re.escape(match.group(1)))

re.sub(r'([^\\])', escape_repl, string)

Example:

>>> print re.sub(r'([^\\])', escape_repl, '[^$]')
\[[\W\[]*\^[\W\^]*\$[\W\$]*\][\W\]]*

I think this is what you are trying to do, but it is a little unclear from your question. Please provide some sample strings and expected results if this isn't what you're looking for.