That was the Pythonic approach until 2006. With Python 2.5 the Pythonic solution was often to use defaultdict:
>>> from collections import defaultdict
>>> words = ['a', 'the', 'an', 'a', 'an', 'the']
>>> d = defaultdict(int)
>>> for word in words:
... d[word] += 1
...
>>> d
defaultdict(<type 'int'>, {'a': 2, 'the': 2, 'an': 2})
It's a bit more cumbersome, but the performance is better, and defaultdict(list)[key].append() is much better than setdefault(key, []).append(value).
In modern Python (starting with Python 2.7, released in 2010), the Pythonic solution is collections.Counter:
>>> from collections import Counter
>>> words = ['a', 'the', 'an', 'a', 'an', 'the']
>>> Counter(words)
Counter({'a': 2, 'the': 2, 'an': 2})
or dict(Counter(words)) if you want the result to return an actual dict instead of a Counter instance.
