python Counter类

from collections import Counter

这个是python内置的，Counter(iterable-or-mapping)可以对里面的各个element进行计数，返回的也是键值对，本身Counter就是字典的子类

比如

In:

words = ['red','blue','red','green','blue','blue']

Counter(words)

Out:

Counter({'blue': 3, 'red': 2, 'green': 1})

In:

Counter({'a':3,'b':5,'c':7})

Out:

Counter({'c': 7, 'b': 5, 'a': 3})