The return function of the advanced Python

<title>return function</title> return function

The Python function returns not only data types such as int, str, list, dict, but also functions.
To give a chestnut: Define a function f () and let it return a function g

1. def F():
2.    Print ' call F () ... '
3.    #定义函数g
4.     def G():
5.        Print ' Call g (... ')
6.    #返回函数g
7.    returnG

Call the function f, and we'll get a function of the F return:

1.>>> x = f()   # 调用f()
2.call f()...
3.>>> x   # 变量x是f()返回的函数：
4.0x1037bf320>
5.>>> x()   # x指向函数，因此可以调用
6.call g()...   # 调用x()就是执行g()函数定义的代码

Note that the return function and return value are distinguished:

1.def myabs():
2.    return abs   # 返回函数
3.def myabs2(x):
4.    return abs(x)   # 返回函数调用的结果，返回值是一个数值

The return function can delay execution of some computations. For example, if you define a normal sum function:

1.def calc_sum(lst):
2.    return sum(lst)

When the Calc_sum () function is called, the result is calculated and obtained immediately:

1.>>> calc_sum([1234])
2.10

However, if you return a function, you can "defer calculation":

1.def calc_sum(lst):
2.    def lazy_sum():
3.        return sum(lst)
4.    return lazy_sum

The call to Calc_sum () does not calculate the result, but instead returns the function:

1.>>> f = calc_sum([1234])
2.>>> f
3.0x1037bfaa0>

The result is calculated when a call is made to the returned function:

1.f()
2.10

Since the function can be returned, we can decide in the subsequent code whether or not to invoke the function.

For example, to write a function Calc_prod (LST), it receives a list, returns a function, and returns a function that calculates the product of the parameter.

1. def calc_prod(LST):
2.     def prob():
3.         def F(x, y):
4.            returnX*y
5.        returnReduce (F,LST,1)
6.    returnProb
7.
8.f = Calc_prod ([1,2,3,4])
9.PrintF ()

The return function of the advanced Python