Closures and decorators

Closure

Inner and outer functions are nested , The inner function refers to Not Global variables , The external function returns the object of the internal function
advantage : Renew the life of variables shortcoming : Waste of memory

#  Inner and outer functions are nested 
def outer(a, b):
    def inner():

#  Internal functions refer to non global variables under the scope of external functions 
        print(a + b)
        
#  The outer function returns the inner function object 
    return inner
outer(5, 9)()

def f1(n):
    def f2():
        list1 = [i for i in range(1, n+1)]
        print(list1)
    return f2
f1(9)()

Decorator

Without changing the original function , Additional function extensions to existing functions .
Do not modify the existing function Source code and Call mode Add new function

The difference between closures and decorators ： The decorator is essentially a closure function , But when the decorator has only one parameter and is a function type , He's the decorator , Otherwise, it is closure

#  Use the idea of closure to realize   Calculate the program usage time  print(" It's a fine day today ")
import time

def outer(f):
    def inner():
        start = time.time()
        f()
        end = time.time()
        print(end - start-1)
    return inner

@outer  # call   Decorator outer
def func():  # func  Parameters passed into the decorator  f
    print(" It's a fine day today ")
    time.sleep(1)

func() #  Equate to innr()

Universal decorator

# The inner function is consistent with the decorated function { Parameters are consistent , Return consistent }
# Define a decorator , Add to the program  print(" Trying to perform addition ")  Program function   Realize the addition of several numbers by passing parameters 
def outer(f):
    def inner(*args):
        print(" Trying to perform addition ")
        f(*args)
    return inner

@outer
def f1(*args):
    print(sum(args))
f1(5, 9, 9, 45, 34)

# Define a decorator   Add <p> </p>
def outer(f):
    def inner():
        return "<p>" + f() + "</p>"
    return inner

@outer
def func():
    return " Life is too short , I use python"
print(func())

Multi layer decorator

# The decorator on the first floor decorates   The second layer is decorated with ornaments 
# The first ornament 
def outer(f):
    def inner():
        print(" This is a decorator 1 Start of execution ")
        f()
        print(" This is a decorator 1 End of execution ")
    return inner
# The second ornament 
def outer2(f):
    def inner2():
        print(" This is a decorator 2 Start of execution ")
        f()
        print(" This is a decorator 2 End of execution ")
    return inner2

@outer
@outer2
def func():
    print(" Life is too short , I use python")
func()

 Execution results ============>
 This is a decorator 1 Start of execution 
 This is a decorator 2 Start of execution 
 Life is too short , I use python
 This is a decorator 2 End of execution 
 This is a decorator 1 End of execution