Dictionaries with variable default.

[Antoon Pardon]

Is it possible to have a default dictionary where the default is dependant
on the key?

I was hoping something like this might work:
>>> m = defaultdict(lambda key: key+1)

But it obviously doesn't:
>>> m[3]

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: <lambda>() takes exactly 1 argument (0 given)

-- 
Antoon Pardon