python：转换频率图列表的快速方法

Question

[“a”，“a”，“a”，“B”，“B”]

词典 {A'：3， “B”：3}

我做了下面这样的事情，但我觉得有一个更快/更短的方法吗

frequencyMap = dict()
letters = ["A","A","A","B","B","B"]

for letter in letters:
    if letter not in frequencyMap:
        frequencyMap[letter] = 0
    frequencyMap[letter] += 1

Answer 1

在Python2.7（或更新版本）中，可以使用collections.Counter

collections.Counter（）

计数器是将元素存储为字典键的容器，其计数存储为字典值

import collections
a = [1,1,1,1,2,2,2,2,3,3,4,5,5]
counter=collections.Counter(a)
print(counter)
# Counter({1: 4, 2: 4, 3: 2, 5: 2, 4: 1})

Answer 2

from collections import Counter

print(Counter(["A","A","A","B","B","B"]))