我终于弄懂了Python的装饰器（二）

此系列文档：

1. 我终于弄懂了Python的装饰器（一）

2. 我终于弄懂了Python的装饰器（二）

3. 我终于弄懂了Python的装饰器（三）

4. 我终于弄懂了Python的装饰器（四）

2、装饰器的高级用法

将参数传递给装饰函数

＃它不是黑魔法，只是给包装（wrapper）传递参数：

def a_decorator_passing_arguments(function_to_decorate):
    def a_wrapper_accepting_arguments(arg1, arg2):
        print("I got args! Look: {0}, {1}".format(arg1, arg2))
        function_to_decorate(arg1, arg2)
    return a_wrapper_accepting_arguments

＃由于当您调用装饰器返回的函数时，调用的包装器（wrapper），将参数传递给被包装器包装的函数

@a_decorator_passing_arguments
def print_full_name(first_name, last_name):
    print("My name is {0} {1}".format(first_name, last_name))

print_full_name("Peter", "Venkman")
# 输出:
#I got args! Look: Peter Venkman
#My name is Peter Venkman

将参数传递给装饰器

关于将参数传递给装饰器自己，您怎么认为？

由于装饰器必须接受一个函数做为参数，因此这可能会有些别扭。

所以，您不能将装饰函数的参数直接传递给装饰器。

在寻求解决方案以前，让咱们写一些提醒：

＃装饰器是普通函数
def my_decorator(func):
    print("I am an ordinary function")
    def wrapper():
        print("I am function returned by the decorator")
        func()
    return wrapper

# 所以，你能够调用它，而不用 "@"

def lazy_function():
    print("zzzzzzzz")

decorated_function = my_decorator(lazy_function)
#输出: I am an ordinary function

# 它输出了 "I am an ordinary function", 由于你只是调用了装饰器，而没有调用函数:
# 这里没有什么神奇的地方，使用'@'

@my_decorator
def lazy_function():
    print("zzzzzzzz")

#outputs: I am an ordinary function

结果同样。
my_decorator”被调用了。
所以，当您使用时@my_decorator，您要告诉Python，经过变量来调用my_decorator标记了的函数。

def decorator_maker():

    print("I make decorators! I am executed only once: "
          "when you make me create a decorator.")

    def my_decorator(func):

        print("I am a decorator! I am executed only when you decorate a function.")

        def wrapped():
            print("I am the wrapper around the decorated function. "
                  "I am called when you call the decorated function. "
                  "As the wrapper, I return the RESULT of the decorated function.")
            return func()

        print("As the decorator, I return the wrapped function.")

        return wrapped

    print("As a decorator maker, I return a decorator")
    return my_decorator

#让咱们新建一个装饰器
new_decorator = decorator_maker()       
#输出:
#I make decorators! I am executed only once: when you make me create a decorator.
#As a decorator maker, I return a decorator

# 让咱们装饰这个函数
def decorated_function():
    print("I am the decorated function.")

decorated_function = new_decorator(decorated_function)
#输出:
#I am a decorator! I am executed only when you decorate a function.
#As the decorator, I return the wrapped function

# 让咱们调用这个函数
decorated_function()

#输出:
#I am the wrapper around the decorated function. I am called when you call the decorated function.
#As the wrapper, I return the RESULT of the decorated function.
#I am the decorated function.

绝不奇怪，跟咱们前边演示的内容同样。

让咱们再作一次彻底同样的事情，可是此次咱们跳过全部讨厌的中间变量：

def decorated_function():
    print("I am the decorated function.")
decorated_function = decorator_maker()(decorated_function)
#输出:
#I make decorators! I am executed only once: when you make me create a decorator.
#As a decorator maker, I return a decorator
#I am a decorator! I am executed only when you decorate a function.
#As the decorator, I return the wrapped function.

# Finally:
decorated_function()    
#输出:
#I am the wrapper around the decorated function. I am called when you call the decorated function.
#As the wrapper, I return the RESULT of the decorated function.
#I am the decorated function.

让咱们把它变的更精简：

@decorator_maker()
def decorated_function():
    print("I am the decorated function.")
#输出:
#I make decorators! I am executed only once: when you make me create a decorator.
#As a decorator maker, I return a decorator
#I am a decorator! I am executed only when you decorate a function.
#As the decorator, I return the wrapped function.

#最终: 
decorated_function()    
#输出:
#I am the wrapper around the decorated function. I am called when you call the decorated function.
#As the wrapper, I return the RESULT of the decorated function.
#I am the decorated function.

嘿，你看到了吗？咱们使用了带有“ @”语法的函数调用！

所以，回到带有参数的装饰器。
若是咱们可使用函数即时生成装饰器，则能够将参数传递给该函数，对吗？

def decorator_maker_with_arguments(decorator_arg1, decorator_arg2):

    print("I make decorators! And I accept arguments: {0}, {1}".format(decorator_arg1, decorator_arg2))

    def my_decorator(func):
        ＃这里传递的参数是闭包的。
        ＃若是您对封包感到不舒服，能够忽略这点。
        print("I am the decorator. Somehow you passed me arguments: {0}, {1}".format(decorator_arg1, decorator_arg2))

            ＃不要混淆装饰器参数和函数参数！        
        def wrapped(function_arg1, function_arg2) :
            print("I am the wrapper around the decorated function.\n"
                  "I can access all the variables\n"
                  "\t- from the decorator: {0} {1}\n"
                  "\t- from the function call: {2} {3}\n"
                  "Then I can pass them to the decorated function"
                  .format(decorator_arg1, decorator_arg2,
                          function_arg1, function_arg2))
            return func(function_arg1, function_arg2)

        return wrapped

    return my_decorator

@decorator_maker_with_arguments("Leonard", "Sheldon")
def decorated_function_with_arguments(function_arg1, function_arg2):
    print("I am the decorated function and only knows about my arguments: {0}"
           " {1}".format(function_arg1, function_arg2))

decorated_function_with_arguments("Rajesh", "Howard")
#输出:
#I make decorators! And I accept arguments: Leonard Sheldon
#I am the decorator. Somehow you passed me arguments: Leonard Sheldon
#I am the wrapper around the decorated function. 
#I can access all the variables 
#   - from the decorator: Leonard Sheldon 
#   - from the function call: Rajesh Howard 
#Then I can pass them to the decorated function
#I am the decorated function and only knows about my arguments: Rajesh Howard

记住它：带参数的装饰器，能够将变量做为参数：

c1 = "Penny"
c2 = "Leslie"

@decorator_maker_with_arguments("Leonard", c1)
def decorated_function_with_arguments(function_arg1, function_arg2):
    print("I am the decorated function and only knows about my arguments:"
           " {0} {1}".format(function_arg1, function_arg2))

decorated_function_with_arguments(c2, "Howard")
#输出:
#I make decorators! And I accept arguments: Leonard Penny
#I am the decorator. Somehow you passed me arguments: Leonard Penny
#I am the wrapper around the decorated function. 
#I can access all the variables 
#   - from the decorator: Leonard Penny 
#   - from the function call: Leslie Howard 
#Then I can pass them to the decorated function
#I am the decorated function and only know about my arguments: Leslie Howard

如您所见，您能够像任何函数传递参数同样传递参数给装饰器。
您甚至能够根据须要使用*args, **kwargs。
可是请记住，装饰器仅被调用一次，仅在Python导入脚本时。以后，您将没法动态设置参数。
当您执行“ import x”时，该函数已经被修饰，所以您没法进行任何更改。

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