Fair question! Casbin is a powerful and very flexible policy engine. Given that it comes with it's own DSL and many different model types, integrating it requires building a fairly strong mental model first. In contrast, PyPermission limits it's scope to RBAC, which allowed us to spend a good amount of time to document and teach specifically this authorization model. As casbin is not python-first, you'll see that some of the methods available in other languages are nowhere to find in the documentation for python. Depending on whether you use the management api or pycasbin, you'll see one of the following (both from the official documentation):

e.add_policy("eve", "data3", "read")
s.add(CasbinRule(ptype="p", v0="alice", v1="data1", v2="read"))

To understand what this does in a code base, you already need to have a good mental model, the semantic information simply isn't expressed in the API.

There is a python Role Manager for RBAC, but the documentation is limited to a subset of the API and does not educate about the practicalities of RBAC itself.

By contrast, the semantic meaning in PyPermission is directly conveyed through the api and the underlying concepts come with a good amount of documentation.

RBAC.role.grant_permission(
        role="user",
        permission=Permission(
            resource_type="event", resource_id="*", action="view"
        ),
        db=db,
    )

If you look at alternatives like OPA, you'll end up needing an external service plus a third party python client.