Pyright issues with NewType

[barraponto]

Despite what is mentioned in docs, I still see errors when adding a factory to the registry using NewType.

This is a sample file where I see the errors on Python 3.12 + svcs 25.1:

from collections.abc import Iterator
from contextlib import contextmanager
from typing import NewType

import svcs
from sqlmodel import Session, create_engine

ContactsDB = NewType("ContactsDB", Session)


@contextmanager
def create_contacts_db() -> Iterator[Session]:
    engine = create_engine("sqlite:///data/wa.db")
    with Session(engine) as session:
        yield session


registry = svcs.Registry()

registry.register_factory(ContactsDB, create_contacts_db)

This is the error I see:

registry.py
  registry.py:20:1 - warning: Type of "register_factory" is partially unknown
    Type of "register_factory" is "(svc_type: type, factory: (...) -> Unknown, *, enter: bool = True, ping: ((...) -> Unknown) | None = None, on_registry_close: ((...) -> Unknown) | Awaitable[Unknown] | None = None) -> None" (reportUnknownMemberType)
  registry.py:20:27 - error: Argument of type "type[ContactsDB]" cannot be assigned to parameter "svc_type" of type "type" in function "register_factory"
    "FunctionType" is not assignable to "type" (reportArgumentType)

[hynek]

Unfortunately, this has been broken by Pyright on purpose and unless I'm mistaken there won't be a good workaround that works across type checkers until PEP 747 is finalized 😔: microsoft/pyright#10596 (comment)

I've added a warning in fe85724 but I'm afraid there isn't anything else we can do from our side.

[barraponto]

I solved it in this specific case by subclassing from Session:

class ContactsDB(Session):
    pass


@contextmanager
def create_contacts_db() -> Iterator[Session]:
    engine = create_engine("sqlite:///data/wa.db")
    with ContactsDB(engine) as session:
        yield session

registry.register_factory(ContactsDB, create_contacts_db)

[hynek]

Yeah, I think that is the correct solution for now.

I will rewrite the docs segment to tell ppl using the subclassing-based approach. I suspect NewType works internally the same, because I couldn't define a NewType for a class that Mypy considered un-subclassable.

[hynek]

I have now adjusted the documentation to using subclassing in 058eeb4

[ctheune]

I'm sure you already have this on your radar, but maybe for future readers: this also happens for register_value() and it doesn't require the client code to use NewType. I can provoke this easily with simple cases:

class Foo:
    pass
f = Foo()
registry.register_value(Foo, f)

resulting in

error: Type of "register_value" is partially unknown
    Type of "register_value" is "(svc_type: type, value: object, *, enter: bool = False, ping: ((...) -> Unknown) | None = None, on_registry_close: ((...) -> Unknown) | Awaitable[Unknown] | None = None) -> None" (reportUnknownMemberType)

I'm not 100% sure it's the same issue, though.

[hynek]

huh, can you give a complete example please?

[ctheune]

Except from the missing instantiation of the registry, that was the full example ... ;)

[ctheune]

There's another issue somewhere around the corner, too. I've switched to using "enter=False" in a database session manager case and that just completely exploded in my face because it's now getting confused about getting the context manager and not the registered type ... but I guess it's still a separate issue ... ?

[hynek]

@ctheune I really need something that I can run. I've added your example to our typing tests and it's passing without any problems: 71ce838