Python supports instance parsing of return functions

This article mainly introduces the example analysis of Python's support for return functions. The editor thinks it is quite good. Now I will share it with you and give it as a reference. Let’s follow the editor to take a look

I recently came into contact with python and saw the concept of returning functions in python. I have only been exposed to function return values ​​before. For example, python can return int, str, list, dict Waiting for type data, what I want to say here is that Python also supports return functions.

First look at the basic syntax of python that supports returning functions

def f():
    print 'call f()...'
    # 定义函数g:
    def g():
        print 'call g()...'
    # 返回函数g:
    return g

Here, the outermost function f will return a function g, which is the function g itself;
Let’s look at the function The calling process; (continued from above)

>>> x = f()   # 调用f()call f()...>>> x   # 变量x就是上面一个最外层函数返回的函数（不是函数值）<function g at 0x1037bf320>
>>> x()   # x指向函数，因此可以调用，这里就是调用内层函数x()的过程call g()...   # 调用x()就是执行g()函数定义的代码

• Only the function of returning function:
  The returning function can delay the execution of some calculations. For example, if you define an ordinary summation function:

def calc_sum(lst):
    return sum(lst)
>>>calc_sum([1,2,3,4])

, the result is directly: 10

However, you can write code by returning the function idea, and you can "delay Calculation"

def calc_sum(lst):
    def lazy_sum():
        return sum(lst)    return lazy_sum

The following is the call:
Note that the following code does not execute the function to calculate the result, but returns the function.

>>> f = calc_sum([1, 2, 3, 4])
>>> f
<function lazy_sum at 0x1037bfaa0>

The result is calculated when the returned function is called

>>>f()10

The following is an example:
Please write a function calc_prod(lst), which receives a list and returns a Function that returns a function that computes the product of its arguments.
Idea: First define a function that can calculate the product, and then return this function.

def calc_prod(lst):
    def lazy_prod():
        def f(x,y):
            return x*y        
        return  reduce(f,lst,1)    
return lazy_prod

f = calc_prod([1, 2, 3, 4])
print f()

                             

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