装饰器

2018年11月6日14:38:00 发表评论 355 views

1、纯函数篇

首先有两个概念需要明白，函数对象和内部函数。

函数对象

在python中函数可以当做一个变量使用，因此也可以当做参数传递给其他的函数：

def invoke_func(func):
    print(f"function:{func.__name__}")
    func()
 
def say_hello():
    print("hello,quanjie!")
invoke_func(say_hello)

def invoke_func(func):

print(f"function:{func.__name__}")

func()

def say_hello():

print("hello,quanjie!")

invoke_func(say_hello)

内部函数

def outer_func():
    print("I am outer")
    def inner_func():
        print("I am inner_func")
    print("invoke inner_func")
    inner_func()
outer_func()

def outer_func():

print("I am outer")

def inner_func():

print("I am inner_func")

print("invoke inner_func")

inner_func()

outer_func()

2、原始装饰器

在这里我将使用原始的方式(函数套用)来实现装饰器的功能。

不带参数的原始装饰器

def decorator(func):
    def wrapper():
        func()
    return wrapper
 
def say_hello():
    print("hello")
say_ = decorator(say_hello)#-----1
say_()#hello

def decorator(func):

def wrapper():

func()

return wrapper

def say_hello():

print("hello")

say_ = decorator(say_hello)#-----1

say_()#hello

没错，这就是一个函数之间的嵌套调用，其中还在decorator中增加了内部函数wrapper，使人感觉多此一举，可以当你看到1处时，你可能就明白了。say_得到的只是一个闭包的环境。

带参数的原始装饰器

def decorator(func):
    def wrapper(*args,**kwargs):
        func(*args,**kwargs)
    return wrapper
 
def say_hello(people):
    print(f"hello,{people}")
 
say_ = decorator(say_hello)
say_("quanjie")#hello,quanjie

def decorator(func):

def wrapper(*args,**kwargs):

func(*args,**kwargs)

return wrapper

def say_hello(people):

print(f"hello,{people}")

say_ = decorator(say_hello)

say_("quanjie")#hello,quanjie

带参有返回值的原始装饰器

def decorator(func):
    def wrapper(*args,**kwargs):
        value = func(*args,**kwargs)
        return value
    return wrapper
 
def say_hello(people):
    return f"hello,{people}"
 
say_ = decorator(say_hello)
print(say_("quanjie"))

def decorator(func):

def wrapper(*args,**kwargs):

value = func(*args,**kwargs)

return value

return wrapper

def say_hello(people):

return f"hello,{people}"

say_ = decorator(say_hello)

print(say_("quanjie"))

可以看到装饰器的作用主要是不修改被装饰的程序而添加新的功能。

3、函数装饰器

原始的装饰器有两点缺点，a、使用过程太过繁琐，b、内部闭包的时候改变了被装饰函数的一下属性等(比如:函数的名称)，因此，python中提供一个@的语法糖和functools包。

不带参数的装饰器

def my_decorator(func):
    @functools.wraps(func)#*******************************
    def wrapper():
        print("Something is happening before the function is called.")
        func()
        print("Something is happening after the function is called.")
    return wrapper
 
@my_decorator
def say_hello():
    print("hello")
say_hello()#*******************************
"""
Something is happening before the function is called.
hello
Something is happening after the function is called.
"""

def my_decorator(func):

@functools.wraps(func)#*******************************

def wrapper():

print("Something is happening before the function is called.")

func()

print("Something is happening after the function is called.")

return wrapper

@my_decorator

def say_hello():

print("hello")

say_hello()#*******************************

"""

Something is happening before the function is called.

hello

Something is happening after the function is called.

"""

带参数的装饰器

"""
带参数的使用方法和原始装饰器的使用方法基本相同
"""
def decorator(func):
    @functools.wraps(func)
    def wrapper(*args, **kwargs):
        func(*args, **kwargs)
    return wrapper

@decorator
def say_hello(people):
    print(f"hello,{people}")
say_hello("quanjie")

"""

带参数的使用方法和原始装饰器的使用方法基本相同

"""

def decorator(func):

@functools.wraps(func)

def wrapper(*args, **kwargs):

func(*args, **kwargs)

return wrapper

@decorator

def say_hello(people):

print(f"hello,{people}")

say_hello("quanjie")

带返回值的装饰器

def decorator(func):
    def wrapper(*args,**kwargs):
        return func(*args,**kwargs)
    return wrapper
@decorator
def return_greeting(name):
    print("Creating greeting")
    return f'Hi {name}'
print(return_greeting("quanjie"))#decorator(return_greeting)("quanjie")
#Hi quanjie

def decorator(func):

def wrapper(*args,**kwargs):

return func(*args,**kwargs)

return wrapper

@decorator

def return_greeting(name):

print("Creating greeting")

return f'Hi {name}'

print(return_greeting("quanjie"))#decorator(return_greeting)("quanjie")

#Hi quanjie

装饰器带有参数的装饰器

"""调用被装饰的函数4次"""
def repeat(num_times):
    def decorator_repeat(func):
        @functools.wraps(func)
        def wrapper_repeat(*args, **kwargs):
            for _ in range(num_times):
                value = func(*args, **kwargs)
            return value
        return wrapper_repeat
    return decorator_repeat
@repeat(num_times=4)
def greet(name):
    print(f"Hello {name}")
    return 123
print(greet("quanjie"))#repat(4)(greet)("quanjie")

"""调用被装饰的函数4次"""

def repeat(num_times):

def decorator_repeat(func):

@functools.wraps(func)

def wrapper_repeat(*args, **kwargs):

for _ in range(num_times):

value = func(*args, **kwargs)

return value

return wrapper_repeat

return decorator_repeat

@repeat(num_times=4)

def greet(name):

print(f"Hello {name}")

return 123

print(greet("quanjie"))#repat(4)(greet)("quanjie")

看着好像有点别扭，其实把它的执行步骤分开解析就明确了；a、调用repeat函数，返回decorator_repeat，但是这个返回值拥有一个num_times变量的闭包环境，b、运行decorator_repeat同时将函数名greet传给它，返回wrapper_repeat，c、运行wrapper_repeat，重复4次执行greet函数，并将最后一次的返回结果返回给最上层的调用者。