Currently, mo.groupdict() always inserts a default value for unmatched named groups.   This is helpful in some use cases and awkward in others.

I propose adding an option to suppress default entries:

>>> # CURRENT WAY
>>> pattern = r'(?P<TITLE>Mrs |Mr |Dr )?(?P<LASTNAME>\w+)(?P<SUFFIX> Phd| JD)?'
>>> print re.match(pattern, 'Dr Who').groupdict()
{'LASTNAME': 'Who', 'SUFFIX': None, 'TITLE': 'Dr '}

>>> # PROPOSED WAY
>>> print re.match(pattern, 'Dr Who').groupdict(nodefault=True)
{'LASTNAME': 'Who', 'TITLE': 'Dr '}

>>> # UPSTREAM VARIANT
>>> print re.match(pattern, 'Dr Who', re.NODEFAULT).groupdict()
{'LASTNAME': 'Who', 'TITLE': 'Dr '}

There is probably a better name than "nodefault", but I would like to see someway to improve the usability of groupdict().