Using the key in collections.defaultdict

collections.defaultdict is great. Especially in conjunction with lambda:

>>> import collections
>>> a = collections.defaultdict(lambda : [None,None])
>>> a['foo']
[None, None]

Is there a way to use the key given (e.g. 'foo') in the lambda? For example (doesn't work):

>>> a = collections.defaultdict(lambda : [None]*key)
>>> a[1]
[None]
>>> a[2]
[None, None]
>>> a
defaultdict(<function <lambda> at 0x02984170>, {1: [None], 2: [None, None]})