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Next: 4.3 regex Up: 4.2 re Previous: 4.2.4 Regular Expression Objects

4.2.5 Match Objects

MatchObject instances support the following methods and attributes:

group ([group1, group2, ...])

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 (i.e. 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 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. 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'.

groups ([default]): 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.)

groupdict ([default]): Return a dictionary containing all the named subgroups of the match, keyed by the subgroup name. The default argument is used for groups that did not participate in the match; it defaults to None.

start ([group])

end ([group])

Return the indices of the start and end of the substring matched by group; group defaults to zero (meaning the whole matched substring). Return None if group exists but did not contribute to the match. For a match object m, and a group g that did contribute to the match, the substring matched by group g (equivalent to m.group(g)) is

m.string[m.start(g):m.end(g)]

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.

span ([group]): For MatchObject m, return the 2-tuple (m.start(group), m.end(group)). Note that if group did not contribute to the match, this is (None, None). Again, group defaults to zero.

pos: The value of pos which was passed to the search() or match() function. This is the index into the string at which the regex engine started looking for a match.

endpos: The value of endpos which was passed to the search() or match() function. This is the index into the string beyond which the regex engine will not go.

re: The regular expression object whose match() or search() method produced this MatchObject instance.

string: The string passed to match() or search().

See Also:

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.