[Python] How to enforce that subclass of abstract class should define a particular inner class...

I have an abstract class from which subclasses will derive. The concrete implementations should include within them an Enum class which holds a set of named constants.

from enum import Enum

class AbstractClass:
def run(self)
print('the values are:')
for enum in ClassEnum:
print(enum.value)
self.speak()

def speak(self):
raise NotImplementedError


class ConcreteClassFirst(AbstractClass):
class ClassEnum(Enum):
RED = 0
GREEN = 1
BLUE = 2

def speak(self)
print('the colors are:')
for enum in ClassEnum:
print(enum.name)


class ConcreteClassSecond(AbstractClass):
class ClassEnum(Enum):
LION = 'scary'
ELEPHANT = 'big'
GIRAFFE = 'tall'

def speak(self)
print('the animals are:')
for enum in ClassEnum:
print(enum.name)


this code in fact gives the correct behaviour, however I would like there to be some sort of notation (similar to the NotImplementedError on the abstract speak() method) That indicates the author of the concrete class should define an inner Enum class called ClassEnum. It is needed in fact for the run() method.

Some ideas are to have something like

class AbstractClass:
class ClassEnum(Enum):
pass

def run(self):
...


but this won't raise an error if the subclass doesn't define its own version of ClassEnum. We could try

class AbstractClass:
class ClassEnum(Enum):
raise NotImplementedError

def run(self):
...


But this predictably raises an error as soon as the AbstractClass is defined

I could try

class AbstractClass:
@property
def ClassEnum(self):
raise NotImplementedError

def run(self):
...


But here it's not clear that in the subclass ClassEnum should in fact be a class. Perhpas this approach with some documentation could be appropriate..

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