Asynccontextmanager provider does not return the instance of the class

[stefanocardarelli]

Hello,

I am trying to bind an interface to an async provider.

In the script I pasted below you will notice it is not strictly necessary to have an async provider, however I am trying to evaluate this library for a project that requires some async functions to instantiate connections, and I'm doing a sort of proof of concept.

I initially tried using inject.attr(IService) on the class attributes but an error suggested me to use autoparams instead off attr for async contexts:

So I switched to a custom constructor for the class to use autoparams on, but I get the following error

It seems the provider does not return the instance I need but the _AsyncGeneratorContextManager itself

This is the current script, it should run as is

import asyncio
from contextlib import asynccontextmanager
from typing import Protocol, Self, runtime_checkable

import inject
from inject import Binder
from pydantic import BaseModel


@runtime_checkable
class IService(Protocol):
    async def do_stuff(self) -> None: ...


class PrintService:
    async def do_stuff(self) -> None:
        print("PrintService is doing stuff")


class MyClass(BaseModel):
    service: IService

    model_config = {"arbitrary_types_allowed": True}

    async def execute(self) -> None:
        await self.service.do_stuff()

    @classmethod
    @inject.autoparams()
    def new(cls, service: IService) -> Self:
        return cls(service=service)


@asynccontextmanager
async def provide_print_service():
    yield PrintService()


def bootstrapper(binder: Binder):
    binder.bind_to_provider(IService, provide_print_service)


inject.configure(bootstrapper)


async def main():
    my_class = MyClass.new()
    await my_class.execute()


asyncio.run(main())

This is the list of the dependencies you need to run this script

• pydantic 2.10.4
• inject 5.2.1

Maybe I'm doing something wrong on my side, can you help me out?
If i need to provide more information please ask.

Thanks in advance!

[ivankorobkov]

Hi,

I think the problem is context managers require an execution scope after which they are destroyed.

Example:

@inject.autoparams()
def example(conn: MockConnection, file: MockFile):
    # Connection and file will be automatically destroyed on exit.
    pass

See, the connection is created on function start and destroyed on function exit.

So, you cannot use the service as an attribute, even if you pass it to constructor. It is destroyed after the constructor exits.

[stefanocardarelli]

Ok, I see, I modified the script above and this actually works as you say

# -- Rest of the code above --
@asynccontextmanager
async def provide_print_service():
    yield PrintService()

def bootstrapper(binder: Binder):
    binder.bind_to_provider(IService, provide_print_service)

inject.configure(bootstrapper)

@inject.autoparams()
async def my_function(service: IService):
    await service.do_stuff()

async def main():
    await my_function()

So what you say it is not possible, with the current state of the library, to bind an interface declared in class attributes to an async constructor (like an inject.attr_async(IInterface) or similar)?
In case, do you think this feature will be available in the future?

Thanks for the assistance