One-step initialization of defaultdict that appends to list?

Question

It would be convenient if a defaultdict could be initialized along the following lines

d = defaultdict(list, ((\'a\', 1), (\'b\', 2), (\'c\', 3), (         


        

Answer 1

>>> kvs = [(1,2), (2,3), (1,3)]
>>> reduce(
...   lambda d,(k,v): d[k].append(v) or d,
...   kvs,
...   defaultdict(list))
defaultdict(, {1: [2, 3], 2: [3]})