python关于的闭包代码实例

闭包（以一个函数里面还有一个函数说明）

只用在第二个函数引用了包含着它的第一个函数定义的变量时，这才叫做闭包

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以函数返回

def curve_pre():
    def curve():
        print("This is a function")
    return curve
f = curve_pre()
f()

输出：This is a function

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闭包 = 函数 + 函数变量（函数定义时候）
def curve_pre():
    a = 25
    def curve(x):
        return a*x*x
    return curve
a = 10
f = curve_pre()
print(f(2))

输出：100

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没有形成闭包情况

a = 25
def curve_pre():
    def curve(x):
        return a*x*x
    return curve
a = 10
f = curve_pre()
print(f(2)）

输出：40

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闭包说明

def curve_pre():
    b = 1
    a = 25
    def curve(x):
        return a*x*x+b
    return curve
a = 10
f = curve_pre()
print(f.__closure__)
print(f.__closure__[0].cell_contents)
print(f.__closure__[1].cell_contents)
print(f(2))

输出

(, )

25

1

101

说明只有在curve函数里用的上一层函数的参数（即时curve_pre()里面）

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非闭包（局部变量）

def f1():
    a = 10
    def f2():
        a = 20 
        print(a)
    print(a)
    f2()
    print(a)
f1()

输出：

10

20

10

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旅行者 从一开始出去

先走2步，共2步；再走3步，共5步；最后走6步，共11步

#全局变量
# origin = 0
# def go(step):
#     global origin
#     new_pos = origin + step
#     origin = new_pos
#     return origin
#
# print(go(2))
# print(go(3))
# print(go(6))

#闭包   #并没有改变origin的值，origin一直都是0
origin = 0
def factory(pos):
    def go(step):
        nonlocal pos  #不是局部变量
        new_pos = pos + step
        pos = new_pos
        return pos
    return go
turist = factory(origin)
print(turist(2))
print(turist(3))
print(turist(6))

#并没有改变origin的值，origin一直都是0