regular expression questions using module re

[Skaperen]

1. i need to match 2 possible forms of a file name. what i did was put one form on each side of a vertical bar ('|'). what i am wondering is how to deal with groups because one form has all 3 groups and the other form has only 2 groups. do i need to have the same number of groups on each side of the vertical bar? or can i use '()' to include a dummy group? or will the .groups() method just return a 3-tuple in one case and a 2-tuple if the other matches?

2. in my expression is a match group for a particular pattern, but if the string has more than one such pattern i want to match the last one and get whatever that pattern is in the string when calling .groups(). how can i be sure of that?

[Gribouillis]

For question 1, the match object will always have 5 groups, for example

>>> import re
>>> p = re.compile(r'(f)(o)(o)|(b)(a)r')
>>> match = p.search('This is a foo thing')
>>> match.groups()
('f', 'o', 'o', None, None)
>>> match = p.search('This is a bar thing')
>>> match.groups()
(None, None, None, 'b', 'a')

For question 2, I don't understand the question. An example would help.

[Skaperen]

if regexp is 'foo(.+)bar' and my string is 'foo123bar...foo789bar' i want to get '789'.

[Gribouillis]

You could use more_itertools.last()

>>> import re
>>> from more_itertools import last
>>> p = re.compile(r'foo(.+?)bar')  # <--- note the ? for the non greedy version of +
>>> s = 'foo123bar...foo789bar'
>>> match = last(p.finditer(s))
>>> match.group(1)
'789'

[Skaperen]

given the answer to #1 being that it returns 5 groups, and filling in what is matched, then #2 is meaningless.