搞不清楚在閉包（closures）中Python是怎樣綁定變量的

看這個例子：

>>> def create_multipliers():... return [lambda x : i * x for i in range(5)]>>> for multiplier in create_multipliers():... print multiplier(2)...

期望得到下面的輸出：

0

2

4

6

8

但是實際上得到的是：

8

8

8

8

8

實例擴展：

# coding=utf-8__author__ = ’xiaofu’# 解釋參考 http://docs.python-guide.org/en/latest/writing/gotchas/#late-binding-closuresdef closure_test1(): ''' 每個closure的輸出都是同一個i值 :return: ''' closures = [] for i in range(4):def closure(): print('id of i: {}, value: {} '.format(id(i), i)) closures.append(closure) # Python’s closures are late binding. # This means that the values of variables used in closures are looked up at the time the inner function is called. for c in closures: c()def closure_test2(): def make_closure(i): def closure(): print('id of i: {}, value: {} '.format(id(i), i)) return closure closures = [] for i in range(4): closures.append(make_closure(i)) for c in closures: c()if __name__ == ’__main__’: closure_test1() closure_test2()

輸出:

id of i: 10437280, value: 3 id of i: 10437280, value: 3 id of i: 10437280, value: 3 id of i: 10437280, value: 3 id of i: 10437184, value: 0 id of i: 10437216, value: 1 id of i: 10437248, value: 2 id of i: 10437280, value: 3

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