How to find out which named regular expression group corresponds to which positional regex group

Serhiy Storchaka storchaka at
Thu Apr 9 09:49:03 CEST 2015

On 08.04.15 16:23, Mattias Ugelvik wrote:
> I'm making a string manipulation tool in which I need to know this correlation.
> Take this example: re.match('(?P<first>a?)(?P<second>b?)', '')
> I need to know that 'first' is group #1, and 'second' is group #2. I
> need this to resolve certain ambiguities. I was hopin

 >>> re.compile('(?P<first>a?)(?P<second>b?)').groupindex
mappingproxy({'first': 1, 'second': 2})

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