Metaclass Protocol Registry

gistfile1.txt

class ProtocolEnum(type):

  registry: Dict[Type[Protocol], Set[Type[Protocol]] = defaultdict(set)

  def __new__(cls, name, bases, dct):
      for base in bases:
          if issubclass(base, Protocol) and not base is Protocol:
              registry[base].add(cls)
      return cls
      
  @classmethod
  def get_enum(cls, protocol: Type[Protocol]) -> Type[enum.Enum]:
      return enum.Enum(protocol.__name__, ((subprot.__name__: subprot.__name__) for subprot in registry[protocol]))

class MyFunProtocol(Protocol, meta=ProtocolEnum):

    def foo(...):
       pass


class MyThingy1(MyFunProtocol):
   def foo(...):
      print('yay')

class MyThingy2(MyFunProtocol):
   def foo(...):
      print('hooray')


>>>print(ProtocolEnum.get_enum(MyFunProtocol).__members__)
{'MyThingy1': 'MyThingy1', 'MyThingy2': 'MyThingy2'}

Obviously we'd want to use fully qualified names as values rather than just class names. (i.e. f'{subprot.__module__.__name__}.{subprot.__name__}')

Then retrieving the type object given an enum value is simple.