Config Inheritance

[wackazong]

Mypy complains at ClassB about: "Definition of "Config" in base class "Model" is incompatible with definition in base class "BaseClass""

What is the problem here?

from pydantic import BaseModel


class BaseClass(BaseModel):
    class Config:
        ...


class Model:
    class Config:
        ...


class ClassA(BaseClass):
    ...


class ClassB(Model, ClassA):
    ...

[wackazong]

This is accepted by mypy, note that Model is now a subclass of BaseModel.

from pydantic import BaseModel


class BaseClass(BaseModel):
    class Config:
        ...


class Model(BaseModel, validate_assignment=True, allow_mutation=True):
    ...


class ClassA(BaseClass):
    ...


class ClassB(Model, ClassA):
    ...

My goals is to use ClassA like a value object (immutable, no business logic) and ClassB like a business model object (mutable, can contain business logic). I would like to inherit fields between the two types, therefore the inheritance of ClassA by ClassB. I would also like to change the pydantic config for ClassB to be mutable. That is why I want to set allow_mutation=False on ClassA and allow_mutation=True on ClassB.

[layday]

Mypy is correct, the two config classes are incompatible with each other, in the same way that you cannot assign an object of class A to a variable declared to be a B if one does not inherit from the other:

class A: ...
class B: ...

class Model:
    a: A

class Submodel(Model):
    a: B  # Invalid

The confusion arises here from the classes being synonymous.

[wackazong]

Ok, thanks for the explanation!