python 闭包

def a():
l=[]
def set_l():
l.append(1)
def get_l():
print l
return set_l, get_l

s,g = a()
In [4]: g()
[]

In [5]: s()

In [6]: s()

In [7]: g()
[1, 1]

In [20]: a=[2,4,5]

In [21]: a[1]+=1

In [22]: a
Out[22]: [2, 5, 5]

In [23]: id(a[1])
Out[23]: 31095920

In [24]: a[1]+=1

In [25]: id(a[1])
Out[25]: 31095908