Why does Field(exclude=True) make the attribute completely inaccessible?

[brian-farrell]

I have a model that I want to store some attributes in that I don't want exposed when the model is returned as an API Response in FastAPI. If I set Field(exclude=True) in the model or I add it to response_model_exclude in the FastAPI route decorator, it doesn't just get excluded from a dump of the model, it becomes completely inaccessible in my backend code.

Here is an example:

@router.get(
    "/profile/",
    response_model=SessionData,
    response_model_exclude={"key_id", "key_ttl"},
    response_model_exclude_none=True,
    name="profile",
    status_code=status.HTTP_200_OK
)
async def get_profile(state_data: dict = Depends(user_session((validator, [CT.SESSION])))):
    """
    User must be logged-in to see their profile
    """
    session_data = state_data.get('SessionData')

    return session_data

Here is the error that I'm seeing:

self = <class 'sesh.examples.models.session.SessionData'>, item = 'key_ttl'

    def __getattr__(self, item: str) -> Any:
        """This is necessary to keep attribute access working for class attribute access."""
        private_attributes = self.__dict__.get('__private_attributes__')
        if private_attributes and item in private_attributes:
            return private_attributes[item]
>       raise AttributeError(item)
E       AttributeError: key_ttl

../../.venv/sesh/lib/python3.12/site-packages/pydantic/_internal/_model_construction.py:237: AttributeError

As soon as I remove key_ttl from response_model_exclude, the attribute becomes accessible again, but then it gets dumped into the API Response, which is not wanted. I see the same behavior if I add Field(exclude=True) to the key_ttl attribute in my model and leave it out of response_model_exclude in the route decorator.

I don't want to make this attribute to completely disappear - I just don't want it dumped/serialized anywhere. What am I missing here?

[brian-farrell]

Apologies - I see the problem now in my code. Please disregard.