python闭包(Closure)，用地址来理解

代码

#closure
def count():
    fs = []
for i in range(1, 4):
        print('in count( ): id(i) = ',id(i), ' | i = ', i)
def f():
             print('in f(): id(i) = ',id(i), ' | i = ', i)
return i*i
        fs.append(f)
return fs

f1, f2, f3 = count()
print(f1)
print(f1())
print(f2)
print(f2())
print(f3)
print(f3())

print("="*20)

def count2():
def f(j):
        print('in f( ): id(j) = ', id(j), ' | j = ', j)
def g():
            print('in g( ): id(j) = ', id(j), ' | j = ', j)
return j*j
return g
    fs = []
for i in range(1, 4):
        print('in count2( ): id(i) = ', id(i), ' | i = ', i)
        fs.append(f(i)) # f(i)立刻被执行，因此i的当前值被传入f()
return fs

F1,F2,F3 = count2()
print(F1)
print(F1())
print(F2)
print(F2())
print(F3)
print(F3())

运行结果

in count( ): id(i) =  2012938704  | i =  1
in count( ): id(i) =  2012938736  | i =  2
in count( ): id(i) =  2012938768  | i =  3
<function count.<locals>.f at 0x000000000106E840>
in f(): id(i) =  2012938768  | i =  3
9
<function count.<locals>.f at 0x000000000106E8C8>
in f(): id(i) =  2012938768  | i =  3
9
<function count.<locals>.f at 0x000000000106E950>
in f(): id(i) =  2012938768  | i =  3
9

---
in count2( ): id(i) =  2012938704  | i =  1
in f( ): id(j) =  2012938704  | j =  1
in count2( ): id(i) =  2012938736  | i =  2
in f( ): id(j) =  2012938736  | j =  2
in count2( ): id(i) =  2012938768  | i =  3
in f( ): id(j) =  2012938768  | j =  3
<function count2.<locals>.f.<locals>.g at 0x000000000106EAE8>
in g( ): id(j) =  2012938704  | j =  1
1
<function count2.<locals>.f.<locals>.g at 0x000000000106EB70>
in g( ): id(j) =  2012938736  | j =  2
4
<function count2.<locals>.f.<locals>.g at 0x000000000106EBF8>
in g( ): id(j) =  2012938768  | j =  3
9

Process finished with exit code 0

分析

• 第一次运行f会跑一次count
• 在f中用i访问外面一层count的局部变量i的时候是用地址访问的，可以看出i在循环中i地址不断地改变,最后访问的是跑完了count时的最终i的地址。
• 如果引入一个函数g来存放那个i的地址就可以输出1*1,2*2,3*3了，因为g中j的地址是不会变的