Story methods should not understand data semantics.

[proofit404]

def a1s1(self, state):
    if self.user.last_login > timezone.now() - timedelta(days=30): # bad
        ...

def a1s1(self, state):
    if self.user.is_active(): # good
        ...

We should not couple shape of data and the way we interpret it to the story definition.

Keep that knowledge to the entities layer.

Entity classes should:

• Force private classes (via generics library).
• Force entities to use attrs frozen.
• Deny validators and converters (use state contract instead).

Suggest to try https://github.com/hchasestevens/bellybutton for this restrictions.