参考来自：http://www.jb51.net/article/65478.htm
def createCounter():
s = [0]
def counter():
s[0] = s[0] + 1
print(s)
return s[0]
return counter
counterA = createCounter()
print(counterA(),counterA(),counterA(),counterA())
输出：
[1]
[2]
[3]
[4]
1 2 3 4
当返回函数引用了循环变量或者后续会发生变化的变量时，这个变量会一直跟随该返回函数
