Python-сообщество

(?...)
    This is an extension notation (a '?' following a '(' is not meaningful otherwise). The first character after the '?' determines what the meaning and further syntax of the construct is. Extensions usually do not create a new group; (?P<name>...) is the only exception to this rule. Following are the currently supported extensions.

(?:...)
    A non-capturing version of regular parentheses. Matches whatever regular expression is inside the parentheses, but the substring matched by the group cannot be retrieved after performing a match or referenced later in the pattern.

  
>>> import re
>>> 
>>> match = re.search(r'(..)(..)(..)', 'abcdef')
>>> match.groups()
('ab', 'cd', 'ef')
>>> 
>>> match = re.search(r'(..)(?:..)(..)', 'abcdef')
>>> match.groups()
('ab', 'ef')
>>>