Python regex strange behavior [duplicate]

Question

I've discovered something that I can't explain in Python re module. Compilation of (a*)* or (a*|b)* throws an error:

raise error, v # invalid expression sre_constants.error: nothing to repeat

I've tested this regexp in javascript and it seems to be ok.

Is it a bug?

Answer 1

Yes, it's a bug (or at least a misfeature). It's complaining that if a* matches nothing, it doesn't know how to capture 0 or more "nothings".

Answer 2

A bug in Python.

http://bugs.python.org/issue2537

http://bugs.python.org/issue214033

Maybe a "bug" is not the correct word here. Different kind of interpretation...