uncalled-for

Async dependency injection for Python functions.

Declare what your function needs as parameter defaults. They show up resolved when the function runs. No ceremony, no container, no configuration.

from uncalled_for import Depends

async def get_db():
    db = await connect()
    try:
        yield db
    finally:
        await db.close()

async def handle_request(db: Connection = Depends(get_db)):
    await db.execute("SELECT 1")

Features

Zero dependencies — standard library only
Async-native — built on AsyncExitStack and ContextVar
Context manager lifecycle — sync and async generators get proper cleanup
Nested dependencies — dependencies can depend on other dependencies
Caching — each dependency resolves once per call, even if referenced multiple times
Call arguments — a factory can reference the arguments of the call it serves

Call arguments

A factory sometimes needs a value from the call itself, not from another dependency. CallArgument declares that reference:

from uncalled_for import CallArgument, Depends

def load_user(user_id: str = CallArgument()) -> User:
    return users[user_id]

async def handle_request(
    user_id: str,
    user: User = Depends(load_user),
):
    ...

The bare form takes the name of the parameter it is declared on. CallArgument("name") names a different parameter of the outer function. The reference sees the same value the outer function receives, whether the caller passed it or another dependency on the outer signature produced it. CallArgument(optional=True) yields None when the outer function has no such argument. References that form a cycle raise CycleError.

Bindings

Depends accepts keyword bindings, so you can wire up an ordinary function without changing it:

async def handle_request(
    user_id: str,
    user: User = Depends(load_user, user_id=CallArgument("user_id")),
):
    ...

A binding that is a Dependency, such as CallArgument(...) or another Depends(...), resolves first and the factory receives its value. Any other value passes through as it is. A binding replaces the factory parameter's own default, which is then never resolved. Two dependencies on the same factory share one cached result only when their bindings match.

Install

pip install uncalled-for

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