ordereddefaultdict.py

import collections


class OrderedDefaultDict(collections.OrderedDict, collections.defaultdict):
    pass


odd = OrderedDefaultDict()
odd.default_factory = list

odd['a'].append(True)
odd['b'].append(False)
odd['c'].append(False)

print(odd.items())
print(odd['d'])

You could also only subclass OrderedDict and define a __missing__ method to to the same thing as default_factory in defaultdict.

FTR collections.Counter can also help depending on your need, and it combines well with collections.OrderedDict: http://rhettinger.wordpress.com/2011/05/26/super-considered-super/