python计算字母出现次数

pyschools Topic 8: Question 7的题目：给定一个单词，输出字母及字母出现次数

Write a function countLetters(word) that takes in a word as argument and returns a dictionary that counts the number of times each letter appears.

python真是方便，可以一行代码搞定

def countLetters(word):
    return dict(sorted([(l,word.count(l)) for l in set(word)]))
print(countLetters('google'))
{'e': 1, 'g': 2, 'l': 1, 'o': 2}