MVC: support business logic layer

[ego]

We have Model and View aka Node, but we lack a way to write code between them.

class PetBusinessLogic:
    def __init__(self, pet):
        self.pet = pet

    @property
    def name1(self):
        return self.pet.name + "!"

    @property
    def name2(self):
        return self.pet.name + "!"


class Pet(SQLAlchemyObjectType):
    class Meta:
        model = PetModel
        name = "Pet"
        interfaces = (relay.Node,)
        batching = True

    def resolve_name1(node, info):
        # write here application logic code for a large project is not good idea.
        # so we need some controller aka PetBusinessLogic
        return PetBusinessLogic(node).name1    # DRY and I would like to initialize it once

    def resolve_name2(node, info):
        return PetBusinessLogic(node).name2  # DRY and I would like to initialize it once

Any suggestions for this design problem?
*(put this PetBusinessLogic into model is also bad idea)

[ego]

@syrusakbary any thoughts?