N Python Class 36 - closure function

In this article authors are all original, For reprint, please indicate the source: https://www.cnblogs.com/xuexianqi/p/12533858.html

One: the basic premise

Closure function with a scope namespace = + + nested function object function

The core point: the name of the relationship is to find the function definition stage prevail

Two: What is the closure function

"Closed" function refers to the function is built-in functions

"Package" function refers to the function of the outer layer contains a reference to the name of the function scope (not on the global scope)

Closure function: namespace application and scope of the nested function +

def f1():
    x = 33333333333333333333
    def f2():
        print(x)
    f2()

x=11111
def bar():
    x=444444
    f1()

def foo():
    x=2222
    bar()

foo()

输出：33333333333333333333
思路：调用的是函数foo(),函数foo()内的x=2222未被调用，调用了函数bar()
     函数bar()内的x=444444未被调用，调用了函数f1()
     函数f1()内定义了x,定义了函数f2(),函数f2()内输出x
     函数f2()内未定义x,就去f1()中，找到了x=33333333333333333333
     最后函数f1()调用了函数f2()，输出33333333333333333333

def f1():
    x = 33333333333333333333
    def f2():
        print('函数f2：',x)
    return f2

f=f1()          # 调用f1()，返回函数f2(),输出：函数f2：33333333333333333333

def foo():
    x=5555
    f()

foo()           # 调用foo(),foo()内调用了f()，也就是调用了f2，输出：函数f2：33333333333333333333

输出：函数f2： 33333333333333333333

Three: Why have closure function == "Closures function

Two kinds of transmission parameters as a function of the body by:

Way: the parameter defines the function body directly molded required parameters

def f2(x):
    print(x)

f2(1)
f2(2)
f2(3)

输出：
1
2
3

Second way: use the closure function

def f1(x): # x=3
    # x=3
    def f2():
        print(x)
    return f2

x=f1(3)
print(x)
x()

输出：
<function f1.<locals>.f2 at 0x02F734A8>
3