003《Python数据分析、挖掘与可视化(第2版)》/例3-5.py
from string import digits
from random import choice

z = ''.join(choice(digits) for i in range(1000))
result = {}
for ch in z:
    result[ch] = result.get(ch,0) + 1
for digit, fre in sorted(result.items()):
    print(digit, fre, sep=':')