Python闭包实现的计数器

#!/usr/bin/env python
#coding=utf-8

def generate_counter():
    CNT = [0]
    def add_one():
        CNT[0] = CNT[0] + 1
        return CNT[0]
    return add_one

counter = generate_counter()
print counter()     # 1
print counter()     # 2
print counter()     # 3