Get nesting of regex groups

[Mattias Ugelvik]

Example: re.compile('(?P<outer>(?P<inner>a))')

How can I detect that 'inner' is a nested group of 'outer'? I know
that 'inner' comes later, because I can use the `regex.groupindex`
(thanks to your help earlier:
https://mail.python.org/pipermail/python-list/2015-April/701594.html).

After looking a bit around, I found this:

>>> sre_parse.parse('(?P<outer>(?P<inner>a))')
[('subpattern', (1, [('subpattern', (2, [('literal', 97)]))]))]

This is all I need, but this is an internal module. Though there
doesn't seem to have been changes from py2 to py3. How inadvisable is
it to use this? Would you blame me?