[Python] FastAPI state not isolated between concurrent users

I have a FastAPI app. In main.py:

@asynccontextmanager
async def lifespan(app: FastAPI):
# Setup
app.state.session_store = {}
yield


In another file, I have the following function:

def get_user_state(request: Request, response: Response) -> AppState:
logger.debug("Session state called")
session_store = request.app.state.session_store
logger.debug(f"Session store: {session_store}")
session_id = request.headers.get("user-id")
if session_id not in session_store:
session_store[session_id] = AppState()
return session_store[session_id]


It gets called with:

@router.post("/endpoint")
async def my_function(
body: MyRequest,
request: Request,
response: Response,
user_state: AppState = Depends(get_user_state)
):


If two instances are running with different user_id values, I can see that the session_store has two different AppState() objects. However, if I add a variable to one of them, it gets added to both. Why??

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