闭包

def make_averager():
    series = []

    def averager(new_value):
        series.append(new_value)
        total = sum(series)
        return total/len(series)
    return averager



avg = make_averager()
print(avg(10))
print(avg(11))
print(avg(12))

#局部变量
print(avg.__code__.co_varnames)
#('new_value', 'total')

#自由变量
print(avg.__code__.co_freevars)
#('series',)

#series的绑定在返回的avg函数的__closure__属性中。avg.__closure__中的各个元素对应于avg.__code__.co_freevars中的一个名称
#这些元素是cell对象，有个cell_contents属性,保存着真正的值
print(avg.__closure__[0].cell_contents)
#[10, 11, 12]