用python统计文件中各个单词出现的次数

import string

d = {}
def choice(str):
s = str.lower() #全部转化为小写
for c in range(97,123): #ASCII 97-122
for i in chr(c): #ASCII 转化为字符
d[i] = s.count(i) #统计s中出现'i'的次数
print(d)

with open('test','r') as f:
choice(f.read())