How do I pythonically set a value in a dictionary if it is None?

You can use dict.setdefault :

count.setdefault('a', 0)

help on dict.setdefault:

>>> print dict.setdefault.__doc__
D.setdefault(k[,d]) -> D.get(k,d), also set D[k]=d if k not in D

setdefault is the best answer, but for the record, the Pythonic way to check for a key in a dict is using the in keyword:

if 'a' not in count:
    count['a'] = 0

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