Question

Given this piece of code(python)

s = [None]*10
def func():
    for i in range(10):
        def update():
            print i,
        s[i] = update

func()
for i in range(10):
    s[i]()

why this result is ten 9s, instead of 0,1,2,3,…9 ?

btw, I’ve also print s[0]~s[9],which are 10 function addresses, and there are different from each other.

Answer 1

You’ve created a bunch of closures over i, but they are all sharing the same (final) value of i

You need to make a tiny modification like this

>>> s = [None]*10
>>> def func():
...     for i in range(10):
...         def update(i=i):
...             print i,
...         s[i] = update
... 
>>> func()
>>> for i in range(10):
...     s[i]()
... 
0 1 2 3 4 5 6 7 8 9