装饰设计师：尽我所能理解它 [英] decorating decorators: try to get my head around understanding it

问题描述

我试图了解装饰装饰器，并想尝试以下方法：

I'm trying to understand decorating decorators, and wanted to try out the following:

假设我有两个装饰器并将它们应用于函数hello：

Let's say I have two decorators and apply them to the function hello:

def wrap(f):
    def wrapper():
        return " ".join(f())
    return wrapper


def upper(f):
    def uppercase(*args, **kargs):
        a,b = f(*args, **kargs)
        return a.upper(), b.upper()
    return uppercase

@wrap
@upper
def hello():
    return "hello","world"

print hello()

然后我必须开始为其他功能添加其他装饰器，
，但通常包装装饰器将包装所有装饰器

Then I have to start adding other decorators for other functions, but in general the wrap decorator will "wrap all of them"

def lower(f):
    def lowercase(*args, **kargs):
        a,b = f(*args, **kargs)
        return a.lower(), b.lower()
    return lowercase

@wrap
@lower
def byebye():
    return "bye", "bye"

现在我要如何用巫婆写一个装饰器，我可以装饰我的上下装饰器：

Now how do I write a decorator, with witch I can decorate my lower and upper decorators:

@wrap
def lower():
    ...

@wrap
def upper():
    ...

要实现通过执行以下操作获得与上述相同的结果：

To achieve the same result as above by only doing:

@upper
def hello():
    ...

@lower
def byebye():
    ...

推荐答案

这是一种使用装饰器装饰装饰器的通用（略为复杂）解决方案（是！）。

Here's a generic (and slightly convoluted) solution for decorating decorators with decorators (Yay!).

# A second-order decorator
def decdec(inner_dec):
    def ddmain(outer_dec):
        def decwrapper(f):
            wrapped = inner_dec(outer_dec(f))
            def fwrapper(*args, **kwargs):
               return wrapped(*args, **kwargs)
            return fwrapper
        return decwrapper
    return ddmain

def wrap(f):
    def wrapper():
        return " ".join(f())
    return wrapper


# Decorate upper (a decorator) with wrap (another decorator)
@decdec(wrap)
def upper(f):
    def uppercase(*args, **kargs):
        a,b = f(*args, **kargs)
        return a.upper(), b.upper()
    return uppercase

@upper
def hello():
    return "hello","world"

print hello()

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