使用类同时作为装饰器和装饰工厂进行操作

Question

考虑下面的装饰函数，它返回一个修饰函数，或参数化的装饰函数<强>或< /强>函数：

from functools import wraps, partial, update_wrapper
from inspect import signature

def wrapit(func=None, *, verb='calling'):
    if func is None:  # return a decoratOR
        return partial(wrapit, verb=verb)
    else:  # return a decoratED
        @wraps(func)
        def _func(*args, **kwargs):
            print(f'{verb} {func.__name__} with {args} and {kwargs}')
            return func(*args, **kwargs)
        return _func

演示：

>>> f = lambda x, y=1: x + y
>>> ff = wrapit(verb='launching')(f)
>>> assert ff(10) == 11
launching <lambda> with (10,) and {}
>>> assert signature(ff) == signature(f)
>>>
>>> # but can also use it as a "decorator factory"
>>> @wrapit(verb='calling')
... def f(x, y=1):
...     return x + y
...
>>> assert ff(10) == 11
launching <lambda> with (10,) and {}
>>> assert signature(ff) == signature(f)

类表单可以如下所示：

class Wrapit:
    def __init__(self, func, verb='calling'):
        self.func, self.verb = func, verb
        update_wrapper(self, func)

    def __call__(self, *args, **kwargs):
        print(f'{self.verb} {self.func.__name__} with {args} and {kwargs}')
        return self.func(*args, **kwargs)

但是，我们如何使类能够在函数形式（由if func is None: return partial...实现）的“装饰器工厂”模式下运行呢 我们如何将这个技巧集成到decorator类中

Answer 1

正如评论中所建议的，您可以使用__new__方法执行此操作：

class Wrapit:
    def __new__(cls, func=None, *, verb='calling'):
        if func is None:
            return partial(cls,verb=verb)
        self = super().__new__(cls)
        self.func, self.verb = func, verb
        update_wrapper(self, func)
        return self

    def __call__(self, *args, **kwargs):
        print(f'{self.verb} {self.func.__name__} with {args} and {kwargs}')
        return self.func(*args, **kwargs)

每当您尝试实例化一个类时，就会调用__new__方法，并且该方法的返回值将用作尝试实例化的结果，即使它不是该类的实例

Answer 2

我接受了@pppery的回答，因为。。。这就是答案。我想通过展示如何通过在父类中编码逻辑来获得更多的重用来扩展这里的答案。这需要将@pppery的逻辑分为__new__和__init__方法

from functools import update_wrapper, partial

class Decorator:
    def __new__(cls, func=None, **kwargs):
        if func is None:
            self = partial(cls, **kwargs)
        else:
            self = super().__new__(cls)
        return update_wrapper(self, func)

    def __init__(self, func=None, **kwargs):
        self.func = func
        for attr_name, attr_val in kwargs.items():
            setattr(self, attr_name, attr_val)

    def __call__(self, *args, **kwargs):
        return self.func(*args, **kwargs)

class Wrapit(Decorator):
    def __new__(cls, func=None, *, verb='calling'):
        return super().__new__(cls, func, verb=verb)

    def __call__(self, *args, **kwargs):
        print(f'{self.verb} {self.func.__name__} with {args} and {kwargs}')
        return super().__call__(*args, **kwargs)

class AnotherOne(Decorator):
    def __new__(cls, func=None, *, postproc=lambda x: x):
        return super().__new__(cls, func, postproc=postproc)

    def __call__(self, *args, **kwargs):
        return self.postproc(super().__call__(*args, **kwargs))

演示：

>>> f = lambda x, y=1: x + y
>>> 
>>> ff = Wrapit(f, verb='launching')
>>> assert ff(10) == 11
launching <lambda> with (10,) and {}
>>> assert signature(ff)  == signature(f) 
>>> 
>>> fff = AnotherOne(postproc=str)(f)  # doing it the decorator factory way
>>> assert fff(10) == str(11)
>>> assert signature(fff)  == signature(f)