Georg Brandl added the comment:
This won't change -- the argument of defaultdict is simply a callable
that is called with no arguments and returns the default value.
It works with `int` because `int()` can be called without arguments and
yields 0; however, `defaultdict` cannot. Therefore, the
New submission from Toshihiro Kamiya :
I found the syntax of collections.defaultdict is confusing, at least to
me.
When I need a defaultdict of int, that is, a defaultdict which contains
int objects, I can write simply:
a = defaultdict(int)
However, when I want a defaultdict of defaultdict of
