Returns one or more subgroups of the match. If there is a single argument, the result is a single string; if there are multiple arguments, the result is a tuple with one item per argument. Without arguments, group1 defaults to zero (the whole match is returned). If a groupN argument is zero, the corresponding return value is the entire matching string; if it is in the inclusive range [1..99], it is the string matching the corresponding parenthesized group. If a group number is negative or larger than the number of groups defined in the pattern, an IndexError exception is raised. If a group is contained in a part of the pattern that did not match, the corresponding result is None. If a group is contained in a part of the pattern that matched multiple times, the last match is returned.
>>> >>> m = re.match(r"(\w+) (\w+)", "Isaac Newton, physicist") >>> m.group(0) # The entire match 'Isaac Newton' >>> m.group(1) # The first parenthesized subgroup. 'Isaac' >>> m.group(2) # The second parenthesized subgroup. 'Newton' >>> m.group(1, 2) # Multiple arguments give us a tuple. ('Isaac', 'Newton')
If the regular expression uses the (?P...) 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<first_name>\w+) (?P<last_name>\w+)", "Malcolm Reynolds") >>> m.group('first_name') 'Malcolm' >>> m.group('last_name') 'Reynolds'
Named groups can also be referred to by their index:
>>> >>> m.group(1) 'Malcolm' >>> m.group(2) 'Reynolds'
If a group matches multiple times, only the last match is accessible:
>>> >>> m = re.match(r"(..)+", "a1b2c3") # Matches 3 times. >>> m.group(1) # Returns only the last match. 'c3'
Return a tuple containing all the subgroups of the match, from 1 up to however many groups are in the pattern. The default argument is used for groups that did not participate in the match; it defaults to None. (Incompatibility note: in the original Python 1.5 release, if the tuple was one element long, a string would be returned instead. In later versions (from 1.5.1 on), a singleton tuple is returned in such cases.)
>>> >>> m = re.match(r"(\d+)\.(\d+)", "24.1632") >>> m.groups() ('24', '1632')
If we make the decimal place and everything after it optional, not all groups might participate in the match. These groups will default to None unless the default argument is given:
>>> >>> m = re.match(r"(\d+)\.?(\d+)?", "24") >>> m.groups() # Second group defaults to None. ('24', None) >>> m.groups('0') # Now, the second group defaults to '0'. ('24', '0')