Allow Channel objects to be created outside of async contexts

[FHTMitchell]

Fixes #161

[FHTMitchell]

Is it expected that people will want to re-use channels? In that case this will cause errors if someone tries to re-use it. In that case we should use an ephemeral _loop in _create_connection rather than setting it as a field.

[vmagamedov]

Is it expected that people will want to re-use channels? In that case this will cause errors if someone tries to re-use it. In that case we should use an ephemeral _loop in _create_connection rather than setting it as a field.

I think that the whole point in removing loop argument in all public-facing APIs in asyncio and here in grpclib is to assume that we always use implicitly one global event-loop to greatly simplify API.

Only in tests I know that this is not true and now also in your example with IPython.

Your PR LGTM, only mypy has some concerns.

[vmagamedov]

I liked your previous version of setting self._loop property here

[FHTMitchell]

Hey, so I will do this, but be aware that this will mean that the following code in ipython will fail (and yes, this is absolutely something I want to do when debugging):

>>>	channel = Channel(...)
...
>>>	async with channel as ch:
...		  client = FooBase(ch)
...		  r1 = await client.bar(...)
...
>>>	async with channel as ch:
...		  client = FooBase(ch)
...		  r2 = await client.bar(...)  # this will fail because we still hold the previous loop
...

When you move to 0.5 you'll want to grab the loop explicitly at the callsite (using asyncio.get_running_loop or, even better, just use the asyncio global methods directly). This emulates doing that. By storing the loop, you're keeping a closed loop around which is not intended behaviour for asyncio.

I don't think there are any benefits in doing it the way we did it before except maybe slightly cleaner code.

Can you confirm this is what you want?

[vmagamedov]

Strange but I can't reproduce your error, even with stock grpclib with no changes.

Python 3.9.13 (main, May 24 2022, 21:28:31)
Type 'copyright', 'credits' or 'license' for more information
IPython 8.4.0 -- An enhanced Interactive Python. Type '?' for help.

In [1]: from grpclib.client import Channel

In [2]: from helloworld.helloworld_pb2 import HelloRequest

In [3]: from helloworld.helloworld_grpc import GreeterStub

In [4]: channel = Channel('127.0.0.1', 50051)

In [5]: async with channel as ch:
   ...:     client = GreeterStub(ch)
   ...:     r1 = await client.SayHello(HelloRequest(name="Dr. Strange"))
   ...:

In [6]: async with channel as ch:
   ...:     client = GreeterStub(ch)
   ...:     r2 = await client.SayHello(HelloRequest(name="Dr. Strange"))
   ...:

In [7]: r1
Out[7]: message: "Hello, Dr. Strange!"

In [8]: r2
Out[8]: message: "Hello, Dr. Strange!"

Which version of IPython do you have?

BTW, as I said before you don't have to use async with to use a channel, like this:

In [4]: channel = Channel('127.0.0.1', 50051)

In [5]: greeter = GreeterStub(channel)

In [6]: await greeter.SayHello(HelloRequest(name='Dr. Strange'))
Out[6]: message: "Hello, Dr. Strange!"

In [7]: await greeter.SayHello(HelloRequest(name='Dr. Strange'))
Out[7]: message: "Hello, Dr. Strange!"

This is fine for IPython sessions or if you want to close the channel manually.

[vmagamedov]

Placing assert self._loop is not None before using self._loop property will do the trick for mypy, this is probably the simplest way of telling to mypy that variable was initialised. If self._protocol is not None then also self._loop is not None.