Use of generics in requests typing

Currently the requests typing makes heavy use of unions. For example the parameter type is:
https://github.com/python/typeshed/blob/f99e8b0615182bb0f17d9d126019d8d72c207ab3/stubs/requests/requests/sessions.pyi#L97-L103

The issue with this approach is that the type system can't keep track of which type has been chosen for a given field. For example, running pyright on this code:

from requests import Session

session = Session()
session.params = {}
reveal_type(session.params)

Shows us that the type system immediately "forgets" that our parameters are definitely in a dictionary:

test.py:5:13 - information: Type of "session.params" is "dict[str | bytes | int | float, str | bytes | int | float | Iterable[str | bytes | int | float] | None]"
0 errors, 0 warnings, 1 information

If we could make Session (as well as other classes such as Request) generic over the parameter type (as well as other fields), then we could keep track of this kind of state. For example, it might look like:

session: Session[dict] = Session()

Inizia con la sezione collegata di requests/requests/sessions.pyi intorno alle righe 97-103, quindi esamina come sono tipizzati Session e Request. Usa l’esempio pyright fornito per valutare se i tipi dei parametri generici rimangono specifici dopo un’assegnazione; il lavoro è completato quando il design generico proposto è definito in modo coerente per le classi interessate e conserva i tipi dei campi selezionati.