8.17. RE Group¶

8.17.1. Rationale¶

Match particular parts of a string
Possible to name matches

8.17.2. Syntax¶

Define:

(...) - Positional group

(?P<name>...) - Named group

(?:...) - Non-matching group

(?#...) - Comment

Backreference:

(?P=name)- Backreferencing by group name

\number - Backreferencing by group number

Example:

(?P<tag><.*?>)text(?P=tag)

(?P<tag><.*?>)text\1

(.+) \1 matches the the or 55 55

(.+) \1 not matches thethe (note the space after the group)

8.17.3. Positional Groups¶

>>> import re
>>>
>>>
>>> TEXT = 'Yuri Gagarin launched to space on Apr 12th, 1961 at 6:07 am.'
>>>
>>> pattern = r'(\w+) (\w+)'
>>> result = re.match(pattern, TEXT)
>>>
>>> result
<re.Match object; span=(0, 12), match='Yuri Gagarin'>
>>>
>>> result.group()
'Yuri Gagarin'
>>>
>>> result.group(1)
'Yuri'
>>>
>>> result.group(2)
'Gagarin'
>>>
>>> result.groups()
('Yuri', 'Gagarin')

8.17.4. Named Groups¶

Usage of group in re.match()

>>> import re
>>>
>>>
>>> TEXT = 'Yuri Gagarin launched to space on Apr 12th, 1961 at 6:07 am.'
>>>
>>> pattern = r'(?P<firstname>\w+) (?P<lastname>\w+)'
>>> result = re.match(pattern, TEXT)
>>>
>>> result.group('firstname')
'Yuri'
>>>
>>> result.group('lastname')
'Gagarin'
>>>
>>> result.group(1)
'Yuri'
>>>
>>> result.group(2)
'Gagarin'
>>>
>>> result.groups()
('Yuri', 'Gagarin')
>>>
>>> result.groupdict()
{'firstname': 'Yuri', 'lastname': 'Gagarin'}

8.17.5. Use Case - 0x01¶

>>> import re
>>>
>>>
>>> line = 'value=123'
>>>
>>> re.findall(r'(\w+)\s?=\s?(\d+)', line)
[('value', '123')]

>>> import re
>>>
>>>
>>> line = 'value = 123'
>>>
>>> re.findall(r'(\w+)\s?=\s?(\d+)', line)
[('value', '123')]