abstract_helpers.py

from typing import cast, Any, Callable, TypeVar
from abc import ABCMeta as NativeABCMeta
from abc import abstractmethod, abstractproperty

R = TypeVar('R')

class DummyAttribute:
    pass

def abstract_attribute(obj: Callable[[Any], R] | None = None) -> R:
    _obj = cast(Any, obj)
    if obj is None:
        _obj = DummyAttribute()
    _obj.__is_abstract_attribute__ = True
    return cast(R, _obj)

class ABCMeta(NativeABCMeta):

    def __call__(cls, *args : Any, **kwargs : Any) -> NativeABCMeta:
        instance : NativeABCMeta = NativeABCMeta.__call__(cls, *args, **kwargs)
        abstract_attributes = {
            name
            for name in dir(instance)
            if getattr(getattr(instance, name), '__is_abstract_attribute__', False)
        }
        if abstract_attributes:
            raise NotImplementedError(
                "Can't instantiate abstract class {} with"
                " abstract attributes: {}".format(
                    cls.__name__,
                    ', '.join(abstract_attributes)
                )
            )
        return instance
    
class ABC(metaclass=ABCMeta):
    """Helper class that provides a standard way to create an ABC using
    inheritance.
    """
    __slots__ = ()