Mattias Ugelvik wrote:
> Example: re.match('(?P<first>a?)(?P<second>b?)', '')
>
> How can I find out that the group 'first' correlates to the positional
> regex group 1? I need to know this to resolve crucial ambiguities in a
> string manipulation tool I'm making. Looking at spans, as the example
> above illustrates, won't do the job.
>
> I can't see a way to do this through the documented interface (at
> least not in the `re` module?).
Compile and match in two separate steps:
>>> import re
>>> r = re.compile('(?P<first>a?)(?P<second>b?)')
Find the groups' positions:
>>> r.groupindex
{'second': 2, 'first': 1}
Find the matching substrings:
>>> r.match("a").groupdict()
{'second': '', 'first': 'a'}
https://docs.python.org/2.7/library/re.html#re.RegexObject.groupindex
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