[python]统计列表中重复项的出现次数

>>> from collections import defaultdict
>>> d = defaultdict(int)
>>> for x in [1, 2, 3, 1, 2, 3, 1]:
...     d[x] += 1
...
>>> dict(d)
{1: 3, 2: 2, 3: 2}
>>>
>>> c = defaultdict(int)
>>> for y in ['a', 'b', 'a', 'c', 'c']:
...     c[y] += 1
...
>>> dict(c)
{'a': 2, 'c': 2, 'b': 1}

>>> e = defaultdict(int)
>>> for x in [{'a': 1, 'b': 1}, {'a': 2, 'b':1}, {'a': 1, 'c': 3}]:
...     e[x['a']] += 1
...
>>> dict(e)   # 'a': 1 出现2次，'a': 2 出现1次
{1: 2, 2: 1}