defaultdict not defined code example

Example 1: nameerror name 'defaultdict' is not defined

You're not importing defaultdict. Do either:

from collections import defaultdict
or

import collections
d = collections.defaultdict(list)

Example 2: nameerror name 'defaultdict' is not defined

import collections
d = collections.defaultdict(int)
d
defaultdict(<type 'int'>, {})