我上了课Op
:
class Pipeable(type):
def __get__(self, instance, owner):
def pipe_within(*args, **kwargs):
return self(*args, op=instance, **kwargs)
print('piping...')
return pipe_within
class Op(metaclass=Pipeable):
def __init__(self, op=None):
if op is not None:
print('piped!')
self.op = op
self.__dict__[type(self).__name__] = type(self)
我希望Op
类本身可以用作描述符,因为它的元类有__get__
方法,但是代码
op = Op().Op()
不会调用Op.__get__
。为什么呢?
答案 0 :(得分:1)
很难说出你真正想要的东西。但是,在每个新类中为自己添加属性的元类可能更适合您想要的任何内容。
就我能理解你的代码而言,旧的类不会被新的实例引用填充,因为你创建新实例(反过来,获取其他人的参考)。
但是,在第二个版本中,创建属性inisde __new__
似乎很苛刻 - 但您可以实现元类__getattr__
和__dir__
方法,以获得更少复杂的代码:
简单版本适用于类,但不适用于它们的实例 - 因为实例不会触发元类上的__getattr__
:
class Pipeable(type):
_classes = {}
def __new__(metacls, name, bases, namespace, **kwds):
cls = type.__new__(metacls, name, bases, namespace)
metacls._classes[name] = cls
return cls
def __getattr__(cls, attr):
classes = cls.__class__._classes
if attr not in classes:
raise AttributeError
def pipe_within(*args, **kwargs):
return cls(*args, op=classes[attr], **kwargs)
print('piping...')
return pipe_within
def __dir__(cls):
regular = super().__dir__()
return sorted(regular + list(cls.__class__._classes.keys()))
class Op(metaclass=Pipeable):
def __init__(self, op=None):
if op is not None:
print('piped!')
self.op = op
Op.Op()
(另请注意,随着时间的推移,我选择了这个参数命名约定用于元类 - 因为大多数方法都采用用它们创建的类来代替普通类中的“self”,我发现这个命名更容易遵循。虽然不是强制性的,但不一定是“正确的”
但是,我们可以通过直接在创建的类上创建__dir__
和__getattr__
来使其适用于实例。与此相关的是,您正在创建的类已经有__getattr__
或自定义__dir__
,即使在他们的超类中,也必须包含它们。然后,我们不想重新包装我们自己的__dir__
和__getattr__
,所以需要一些额外的关注:
class Pipeable(type):
_classes = {}
def __new__(metacls, name, bases, namespace, **kwds):
cls = type.__new__(metacls, name, bases, namespace)
metacls._classes[name] = cls
original__getattr__ = getattr(cls, "__getattr__", None)
if hasattr(original__getattr__, "_metapipping"):
# Do not wrap our own (metaclass) implementation of __getattr__
original__getattr__ = None
original__dir__ = getattr(cls, "__dir__") # Exists in "object", so it is always found.
# these two functions have to be nested so they can get the
# values for the originals "__getattr__" and "__dir__" from
# the closure. These values could be set on the class created, alternatively.
def __getattr__(self, attr):
if original__getattr__:
# If it is desired that normal attribute lookup have
# less precedence than these injected operators
# move this "if" block down.
try:
value = original__getattr__(self, attr)
except AttributeError:
pass
else:
return value
classes = self.__class__.__class__._classes
if attr not in classes:
raise AttributeError
def pipe_within(*args, **kwargs):
return cls(*args, op=classes[attr], **kwargs)
print('piping...')
return pipe_within
__getattr__._pipping = True
def __dir__(self):
regular = original__dir__(self)
return sorted(regular + list(self.__class__.__class__._classes.keys()))
__dir__.pipping = True
if not original__getattr__ or not hasattr(original__getattr__, "_pipping"):
cls.__getattr__ = __getattr__
if not hasattr(original__dir__, "_pipping"):
cls.__dir__ = __dir__
return cls
def __getattr__(cls, attr):
classes = cls.__class__._classes
if attr not in classes:
raise AttributeError
def pipe_within(*args, **kwargs):
return cls(*args, op=classes[attr], **kwargs)
print('piping...')
return pipe_within
__getattr__._metapipping = True
def __dir__(cls):
regular = super().__dir__()
return sorted(regular + list(cls.__class__._classes.keys()))
class Op(metaclass=Pipeable):
def __init__(self, op=None):
if op is not None:
print('piped!')
Op().Op()
因此,这最终会变得冗长 - 但是通过确保层次结构中的所有类和实例可以看到彼此,无论创建顺序如何,它都“做正确的事”。
此外,弥补复杂性的原因是在类层次结构中正确包装__getattr__
和__dir__
的其他可能的自定义项 - 如果您没有对其进行任何自定义,这可以是一个订单更简单:
class Pipeable(type):
_classes = {}
def __new__(metacls, name, bases, namespace, **kwds):
cls = type.__new__(metacls, name, bases, namespace)
metacls._classes[name] = cls
def __getattr__(self, attr):
classes = self.__class__.__class__._classes
if attr not in classes:
raise AttributeError
def pipe_within(*args, **kwargs):
return cls(*args, op=classes[attr], **kwargs)
print('piping...')
return pipe_within
def __dir__(self):
regular = original__dir__(self)
return sorted(regular + list(self.__class__.__class__._classes.keys()))
cls.__getattr__ = __getattr__
cls.__dir__ = __dir__
return cls
def __getattr__(cls, attr):
classes = cls.__class__._classes
if attr not in classes:
raise AttributeError
def pipe_within(*args, **kwargs):
return cls(*args, op=classes[attr], **kwargs)
print('piping...')
return pipe_within
def __dir__(cls):
regular = super().__dir__()
return sorted(regular + list(cls.__class__._classes.keys()))
答案 1 :(得分:0)
要开始工作,描述符必须是class属性,而不是实例。 这段代码完成了所需的工作。
class Pipeable(type):
_instances = {}
def __new__(cls, name, bases, namespace, **kwds):
namespace.update(cls._instances)
instance = type.__new__(cls, name, bases, namespace)
cls._instances[name] = instance
for inst in cls._instances:
setattr(inst, name, instance)
return instance
def __get__(self, instance, owner):
def pipe_within(*args, **kwargs):
return self(*args, op=instance, **kwargs)
print('piping...')
return pipe_within
class Op(metaclass=Pipeable):
def __init__(self, op=None):
if op is not None:
print('piped!')
self.op = op
Op().Op()