README.md

plain-abc

Another ABC implementation without metaclass.

It is a little bit annoying to have metaclass conflict, especially when trying to use ABC along with other libraries.

plain-abc provides a simple ABC implementation without metaclass.

Installation

pip install plain-abc

Usage

But you can also use plain-abc to solve the problem:

from abc import abstractmethod

from plain_abc import PlainABC


class _SomeHiddenMetaclass(type):
    pass


class Base(metaclass=_SomeHiddenMetaclass):
    pass


class IFoo(PlainABC):
    @abstractmethod
    def foo(self): ...


class Foo(Base, IFoo):
    def foo(self): ...

To extend an abstract class as another abstract class, PlainABC is required to be one of the bases:

from abc import abstractmethod

from plain_abc import PlainABC


class IEntity(PlainABC):
    @abstractmethod
    def get_id(self) -> str: ...


class IProjectile(IEntity, PlainABC):
    @abstractmethod
    def get_speed(self) -> float: ...


class Arrow(IProjectile):
    def get_id(self) -> str: ...
    def get_speed(self) -> float: ...

To skip signature checking, you can add the member names in __abc_concrete_members__ of a subclass:

from abc import abstractmethod
from enum import Enum

from plain_abc import PlainABC


class IEnum(PlainABC):
    @property
    @abstractmethod
    def foo(self) -> str:
        ...


class Foo(IEnum, Enum):
    # for python 3.10 or lower
    __abc_concrete_members__ = ('foo',)
    foo = 'foo'


assert Foo.foo.value == 'foo'

To solve metaclass conflict without plain-abc

Here is an example of metaclass conflict and how to mix ABCMeta with other metaclasses.

from abc import ABC, ABCMeta, abstractmethod


class _SomeHiddenMetaclass(type):
    ...


class Base(metaclass=_SomeHiddenMetaclass):
    ...


class IFoo(ABC):
    @abstractmethod
    def foo(self): ...


# oh no, metaclass conflict!
# class Foo(Base, IFoo):
#     def foo(self): ...


# create a new metaclass to solve the conflict
class NewMetaclass(_SomeHiddenMetaclass, ABCMeta):
    ...


class Foo(Base, IFoo, metaclass=NewMetaclass):
    def foo(self): ...