re.sub and empty groups

Patrick Gaherty pgaherty at
Tue Feb 12 10:56:02 EST 2002

I'm trying something along the following lines:

line = re.sub(r'(a)(b)?(c)',r'\3\2\1',line)

and Python complains about empty groups when (b)? doesn't match.

What's the best way of getting around this?

Thanks in advance.

Patrick Gaherty

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