Python---return function

# -*- coding: utf-8 -*-#  return function # 1. function as return value #  higher order functions can also return a function as a result value in addition to the function as a parameter   Implement a variable parameter summation #  Typically, the summation function is written def calc_sum (*args):    ax = 0     for n in args:        ax =  ax + n    return ax#  can not return the result of a sum, but instead returns the sum of the function def lazy_sum (*args):     def sum ():        ax = 0         for n in args:             ax = ax + n         return ax    return sum#  when we call Lazy_sum (), the return is not the result of the summation, but the sum function f =  lazy_sum (1, 3, 5, 7, 9) #  output is the function sum itself print (f) #  call Sumprint (f ()) #  in this example , we also define the function s in the function lazy_sumUm, and the intrinsic function sum can refer to functions and local variables of the external function lazy_sum #  when Lazy_sum returns the function sum, the relevant parameters and variables are stored in the returned function, a program called the "Closure (Closure)" has great power #   A point to F1 = lazy_sum (1, 3, 5, 7, 9) f2 = lazy_sum (1, 3,  5, 7, 9) print (F1 == F2) # f1 == f2 false# f1 () and F2 () do not affect the results of the call # 2. Closure #  Notice that the returned function references the variable args within its definition, so when a function returns a function, its internal local variables are also referenced by the new function #  Another concern is that the returned function is not executed immediately, Instead, the Def count () is executed until F () is called ():     fs = []    for i  in range (1, 4):         def f ():             return i * i         fs.append (f)     return fsf1, f2, f3 =  Count () #  in the example above, each loop creates a new function and then returns the created 3 functions to the #  result (9, 9, 9) print (F1 (),  F2 (),  F3 ()) #  The reason is that the returned function references the variable I,  But it is not implemented immediately. When all 3 functions return, they refer to the variable i has become 3, so the final result is the 9#  return function does not reference any loop variable, or the subsequent variable #  a function can return a result of a calculation, you can also return a function #  When returning a function, keep in mind that the function is not executed, and do not refer to any variables that may change in the return function

Python---return function