Python：计算多值字典中的值

Question

How can I count the number of a specific values in a multi-value dictionary?

For example, if I have the keys A and B with different sets of numbers as values, I want get the count of each number amongst all of the dictionary's keys.

I've tried this code, but I get 0 instead of 2.

dic = {'A':{0,1,2},'B':{1,2}}
print(sum(value == 1 for value in dic.values()))

Answer 1

Counter is a good option for this, especially if you want more than a single result:

from collections import Counter

from itertools import chain
from collections import Counter
count = Counter(chain(*(dic.values())))

In the REPL:

>>> count
Counter({1: 2, 2: 2, 0: 1})
>>> count.get(1)
2

Counter simply tallies each item in a list. By using chain we treat a list of lists as simply one large list, gluing everything together. Feeding this right to Counter does the work of counting how many of each item there is.