Fix Process.communicate() return type

[Dreamsorcerer]

With mypyc I get:

Traceback (most recent call last):
  File "bluetooth_devices.py", line 216, in switch_to_master
    while await self.is_slave(device_address):
  File "bluetooth_devices.py", line 231, in is_slave
    stdout, stderr = await proc.communicate()
TypeError: tuple[bytes, bytes] object expected; got tuple[bytes, None]

From the docs:

to get anything other than None in the result tuple, the process has to be created with stdout=PIPE and/or stderr=PIPE arguments.

This could be more precise if the Process was Generic and the type depended on the arguments passed..

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

aiohttp-devtools (https://github.com/aio-libs/aiohttp-devtools)
+ tests/test_runserver_cleanup.py:40: error: Unsupported right operand type for in ("bytes | None")  [operator]
+ tests/test_runserver_cleanup.py:41: error: Item "None" of "bytes | None" has no attribute "decode"  [union-attr]

core (https://github.com/home-assistant/core)
+ homeassistant/util/package.py:186: error: Item "None" of "bytes | None" has no attribute "decode"  [union-attr]
+ homeassistant/components/command_line/utils.py:60: error: Item "None" of "bytes | None" has no attribute "strip"  [union-attr]
+ homeassistant/auth/providers/command_line.py:95: error: Item "None" of "bytes | None" has no attribute "splitlines"  [union-attr]

[Dreamsorcerer]

I can add assert is not None to the affected code, or look at making it Generic?

[Dreamsorcerer]

I started an attempt to make it generic in #13385, but I think it'll be fairly complex to get working.

[Dreamsorcerer]

Apparently, I can't even fix the runtime error with a cast...

Jan 13 17:51:17 bthidhub python3[3101]: Traceback (most recent call last):
Jan 13 17:51:17 bthidhub python3[3101]:   File "bluetooth_devices.py", line 216, in switch_to_master
Jan 13 17:51:17 bthidhub python3[3101]:     while await self.is_slave(device_address):
Jan 13 17:51:17 bthidhub python3[3101]:   File "bluetooth_devices.py", line 232, in is_slave
Jan 13 17:51:17 bthidhub python3[3101]:     stdout, _ = cast(tuple[bytes, None], await proc.communicate())
Jan 13 17:51:17 bthidhub python3[3101]: TypeError: tuple[bytes, bytes] object expected; got tuple[bytes, None]

[hauntsaninja]

if you need a workaround, I'd bet await cast(Any, proc).communicate() would do the trick

[Dreamsorcerer]

if you need a workaround, I'd bet await cast(Any, proc).communicate() would do the trick

Yeah, I got it working with await cast(Awaitable[tuple[bytes, None]], proc.communicate()) just now.

Does this PR seem like the right approach, or shall I spend more time getting the Generic PR working?