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Date: Wed, 8 Apr 2015 16:37:06 +0200
Subject: Re: Get the numbering of named regex groups
From: Mattias Ugelvik <uglemat@gmail.com>
To: Peter Otten <__peter__@web.de>
Cc: python-list@python.org
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Xref: csiph.com comp.lang.python:88669

Thank god it's that easy! Err, I mean, thank you! I should have read
the docs more carefully :)

On 08/04/2015, Peter Otten <__peter__@web.de> wrote:
> 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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