The simple example is fixable by anchoring the inner greedy expression, i.e. regex = re.compile(r'(^a+)+b') Perhaps the more general problem was that "The reg

The simple example is fixable by anchoring the inner greedy expression, i.e. regex = re.compile(r'(^a+)+b') Perhaps the more general problem was that "The regular expression that was causing the issue here was rather long and convoluted". A good rule seems to be never have long and convoluted regexs, instead have a pipeline of simple-to-understand regexes that can be independently debugged (I don't know if this could cause performance slowdowns however).