考虑以下装饰器函数,该装饰器函数将返回装饰器函数或参数化的decorat 或函数:
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)
类的形式可能看起来像这样:
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)
但是我们如何使该类能够在功能形式具有的“ decorator factory”模式下运行(由if func is None: return partial...
实现我们如何将这个技巧整合到装饰类中?
如注释中所建议,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(Wrapit,verb=verb)
self = object.__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)
__new__
方法在您尝试实例化一个类时都会被调用,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!