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Mon Dec 4 11:58:17 CET 2006 · https://mail.python.org/pipermail/python-dev/2006-December/070178.html

Ben Wing wrote:
> the only strangeness here is the numbering of groups starting at 1, and 
> making 0 be a special case.  this isn't any more (or less) of a problem 
> for the indexing form than it is for m.group(), and it's well known from 
> various other languages.  we could always consider making groups start 
> at 0 for python 3000, but this seems to me like a gratuitous 
> incompatibility with the rest of the world.

As Greg pointed out, this is just a special case of the fact that subgroups 
can be nested with the ordering governed by the location of the left parenthesis:

.>>> import re
.>>> m = re.match("a(b(c))", "abc")
.>>> m.group(0)
'abc'
.>>> m.group(1)
'bc'
.>>> m.group(2)
'c'

That said, I like the definitions in your last message:

   len(m) == 1 + len(m.groups())
   m[:] == [m.group(0)] + m.groups()
   all(m[i] == m.group(i) for i in range(len(m)))
   all(m[k] == m.group(k) for k in m.groupdict().keys())

The internally inconsistent* m.group() and m.groups() methods could even be 
slated for removal in Py3k (replaced by the subscript operations).

Cheers,
Nick.

*The inconsistency being that group() considers the whole match to be group 0, 
while groups() does not.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
---------------------------------------------------------------
             http://www.boredomandlaziness.org

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[Python-Dev] [NPERS] Re: a feature i'd like to see in python #2: indexing of match objects