Question

对装饰者有很大疑虑。在简单的测试代码下面，请阅读一些初学者的书。

# -*-coding:Latin-1 -*

import sys

# The decorator.
def my_decorator(modified_function):
    """My first decorator."""

    # Modifying modified_function.
    def modifying_function():
        print("--> before")
        ret = modified_function()
        print("<-- after={}".format(ret))
        return ret

    print("Decorator is called with modified_function '{0}'".format(modified_function))

    # Return the modifying function.
    return modifying_function

@my_decorator
def hello_world():
    """Decorated function."""
    print("!! That's all folks !!")
    return (14)

print("Python version = {}".format(sys.version))

# We try to call hello_world(), but the decorator is called.
hello_world()
print("--------------------------------------------------------------")

my_decorator(hello_world)
print("--------------------------------------------------------------")

# Found this other way on the WEB, but does not work for me
my_hello  = my_decorator(hello_world)
my_hello()
print("--------------------------------------------------------------")

对于这段代码，输出对我来说很奇怪。也许这很愚蠢，但是......

Decorator is called with modified_function '<function hello_world at 0x0000011D5FDCDEA0>'
Python version = 3.6.2 (v3.6.2:5fd33b5, Jul  8 2017, 04:57:36) [MSC v.1900 64 bit (AMD64)]
--> before
!! That's all folks !!
<-- after=14
--------------------------------------------------------------
Decorator is called with modified_function '<function my_decorator.<locals>.modifying_function at 0x0000011D5FDCDF28>'
--------------------------------------------------------------
Decorator is called with modified_function '<function my_decorator.<locals>.modifying_function at 0x0000011D5FDCDF28>'
--> before
--> before
!! That's all folks !!
<-- after=14
<-- after=14
--------------------------------------------------------------

在装饰器跟踪之后打印python版本。
在第二次和第三次调用中，print（“Decorator被调用了modified_function ...”）给了我一些奇怪的函数值。至少，不是我的预期。
跟踪（“ - ＆gt; ...”）和（“＆lt; - ...”）加倍。

欢迎对新手进行任何澄清。

Answer 1

您的混淆与您手动使用装饰器的事实有关，但您还使用Python的特殊语法将装饰器应用于定义它们的函数： @my_decorator。你通常不想为同一个功能做这两件事。

试试这个例子，它可以帮助你更好地理解事情：

# after defining my_decorator as before...

def foo():          # define a function for testing with manual decorator application
    print("foo")
print("----")
foo()               # test unmodified function
print("----")
decorated_foo = my_decorator(foo)    # manually apply the decorator (assigning to a new name)
print("----")
decorated_foo()     # test decorated function
print("----")
foo()               # confirm that the original function is still the same
print("----")
foo = my_decorator(foo) # apply the decorator again, replacing the original name this time
print("----")
foo()               # see that the original function has been replaced
print("----")
@my_decorator   # this line applies the decorator for you (like the "foo = ..." line above)
def bar(): 
    print("bar")
print("----")
bar()               # note that the decorator has already been applied to bar
print("----")
double_decorated_bar = my_decorator(bar)   # apply the decorator again, just for fun
print("----")
double_decorated_bar()   # get doubled output from the doubled decorators

Answer 2

哦......好的。我看到光明来了：

double_decorated_bar = my_decorator(bar)   # apply the decorator again, just for fun

没注意@decorator在示例中不存在。再次澄清。

澄清要求装饰者

2 个答案: