MatchObject instances support the following methods and attributes:
If the regular expression uses the (?P<name>...) syntax, the groupN arguments may also be strings identifying groups by their group name. If a string argument is not used as a group name in the pattern, an IndexError exception is raised.
A moderately complicated example:
m = re.match(r"(?P<int>\d+)\.(\d*)", '3.14')
After performing this match, m.group(1) is '3', as is m.group('int'), and m.group(2) is '14'.
Note that m.start(group) will equal m.end(group) if group matched a null string. For example, after m = re.search('b(c?)', 'cba'), m.start(0) is 1, m.end(0) is 2, m.start(1) and m.end(1) are both 2, and m.start(2) raises an IndexError exception.
Jeffrey Friedl, Mastering Regular Expressions, O'Reilly. The Python material in this book dates from before the re module, but it covers writing good regular expression patterns in great detail.