Named groups (?P...)

Question

Named groups (?P<name>...)

Accepted Answer

Named groups are declared with (?P<name>...) and can be retrieved either by name via m.group('level') or by their positional index via m.group(1). The three groups in order are: group 1 = 'level', group 2 = 'date', group 3 = 'msg'. m.group('level') -> 'ERROR', m.group('date') -> '2024-03-01', and m.group(2) is the second capturing group which is also 'date', so it returns '2024-03-01'. Named groups shine in production log parsers and data pipeline code because the name documents the intent. When the pattern changes and group positions shift, code that uses m.group('date') keeps working; code that uses m.group(2) silently returns the wrong field. You can also use m.groupdict() to get all named groups as a dict, which maps cleanly to a database row or a dataclass.