Python 装饰器

def uppercase_decorator(function): # 接受一个function作为参数
    def wrapper():
        func = function() # func即为function的返回值
        make_uppercase = func.upper()
        return make_uppercase # wrapper函数返回 function返回值 的大写形式
    return wrapper # uppercase_decorator函数返回 一个叫做 wrapper 的函数

def say_hi():
    return 'hello there'

decorate = uppercase_decorator(say_hi) # 把say_hi这个函数作为参数传到uppercase_decorator函数

## 执行过程如下
# def uppercase_decorator(function): # 接受say_hi作为参数
#    def wrapper():
#        func = function() # say_hi的返回值即'hello there'赋值给func
#        make_uppercase = func.upper() # 对 'hello there' 进行大写转换
#        return make_uppercase # wrapper函数返回 'HELLO THERE'
#    return wrapper # uppercase_decorator函数返回 一个叫做 wrapper 的函数, 而 wrapper的返回值正是 'HELLO THERE'

decorate() # decorate 正是上述的wrapper函数，对其加()即调用，故返回 'HELLO THERE'
# 'HELLO THERE'

第二种方式从表达上更像重写了say_hi函数，使其增加了一个返回值大写的功能

@uppercase_decorator
def say_hi():
    return 'hello there'

say_hi()
# 'HELLO THERE'

def split_string(function):
    def wrapper():
        func = function()
        splitted_string = func.split()
        return splitted_string
    return wrapper
# ----------------------------------
@split_string
@uppercase_decorator
def say_hi():
    return 'hello there'
say_hi()
# ['HELLO', 'THERE']

注意：参数传给 wrap 函数

def decorator_with_arguments(function):
    def wrapper_accepting_arguments(arg1, arg2):
        print("My arguments are: {0}, {1}".format(arg1,arg2))
        function(arg1, arg2)
    return wrapper_accepting_arguments


@decorator_with_arguments
def cities(city_one, city_two):
    print("Cities I love are {0} and {1}".format(city_one, city_two))
    
	# 将cities(city_one, city_two)传给decorator_with_arguments 得到wrapper_accepting_arguments函数
	# wrapper_accepting_arguments函数
		# 1. 执行 print("My arguments are: {0}, {1}".format(arg1,arg2))
		# 2. 执行 function(arg1, arg2)， 即 print("Cities I love are {0} and {1}".format(city_one, city_two))
		
cities("Nairobi", "Accra")

# My arguments are: Nairobi, Accra
# Cities I love are Nairobi and Accra

def a_decorator_passing_arbitrary_arguments(function_to_decorate):
    def a_wrapper_accepting_arbitrary_arguments(*args,**kwargs):
        print('The positional arguments are', args)
        print('The keyword arguments are', kwargs)
        function_to_decorate(*args)
    return a_wrapper_accepting_arbitrary_arguments

@a_decorator_passing_arbitrary_arguments
def function_with_no_argument():
    print("No arguments here.")

function_with_no_argument()
# The positional arguments are ()
# The keyword arguments are {}
# No arguments here.

@a_decorator_passing_arbitrary_arguments
def function_with_arguments(a, b, c):
    print(a, b, c)

function_with_arguments(1,2,3)
# The positional arguments are (1, 2, 3)
# The keyword arguments are {}
# 1 2 3

@a_decorator_passing_arbitrary_arguments
def function_with_keyword_arguments():
    print("This has shown keyword arguments")

function_with_keyword_arguments(first_name="Derrick", last_name="Mwiti")

# The positional arguments are ()
# The keyword arguments are {'first_name': 'Derrick', 'last_name': 'Mwiti'}
# This has shown keyword arguments