装饰装饰:试着理解它

Question

我正在尝试了解装饰装饰器,并想尝试以下内容:

假设我有两个装饰器并将它们应用于函数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函数添加其他装饰器,但一般来说,wrap装饰器将"包装所有这些"

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"

现在我如何写一个装饰器,我可以装饰我的下装饰器和上装饰器:

@wrap
def lower():
    ...

@wrap
def upper():
    ...

通过以下方式实现与上述相同的结果:

@upper
def hello():
    ...

@lower
def byebye():
    ...

Answer 1

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

Python中的装饰器

 @foo
 def bar(...): ...

等于

 def bar(...): ...
 bar = foo(bar)

你想得到的效果

@wrap
@upper
def hello(): ....

即

hello = wrap(upper(hello))

所以wrap应该在返回值上调用upper:

def upper_with_wrap(f):
   def uppercase(...): ...
   return wrap(uppercase)

这也相当于在该函数上应用装饰器:

def upper_with_wrap(f):
   @wrap
   def uppercase(...): ...
   # ^ equivalent to 'uppercase = wrap(uppercase)'
   return uppercase

Answer 2

这是一个通用(并且有点复杂)的解决方案,用于装饰装饰器(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()