[FIXED] Exception ignored in message on program exit

Issue

I initially wanted to do async stream communication on windows.

from asyncio import *
from asyncio.subprocess import PIPE, STDOUT, DEVNULL
import sys

async def test(exe):
  inst = await create_subprocess_exec(exe, stdin=PIPE, stdout=PIPE, stderr=STDOUT)
  inst.stdin.close()
  inst.wait()

# for subprocess' pipes on Windows
def initialize_async():
  if sys.platform == 'win32':
    set_event_loop(ProactorEventLoop())
  return get_event_loop()

loop = initialize_async()
loop.run_until_complete(test('attrib.exe'))
loop.close()

The above code generates the following.

Exception ignored in: <bound method BaseSubprocessTransport.__del__ of <_WindowsSubprocessTransport closed pid=65088 running stdin=<_ProactorWritePipeTransport closed> stdout=<_ProactorReadPipeTransport closing fd=476 read=<_OverlappedFuture cancelled>>>>
Traceback (most recent call last):
  File "C:\Program Files\Python36\lib\asyncio\base_subprocess.py", line 132, in __del__
    self.close()
  File "C:\Program Files\Python36\lib\asyncio\base_subprocess.py", line 106, in close
    proto.pipe.close()
  File "C:\Program Files\Python36\lib\asyncio\proactor_events.py", line 84, in close
    self._loop.call_soon(self._call_connection_lost, None)
  File "C:\Program Files\Python36\lib\asyncio\base_events.py", line 573, in call_soon
    self._check_closed()
  File "C:\Program Files\Python36\lib\asyncio\base_events.py", line 357, in _check_closed
    raise RuntimeError('Event loop is closed')
RuntimeError: Event loop is closed
Exception ignored in: <object repr() failed>
Traceback (most recent call last):
  File "C:\Program Files\Python36\lib\asyncio\proactor_events.py", line 95, in __del__
    warnings.warn("unclosed transport %r" % self, ResourceWarning,
  File "C:\Program Files\Python36\lib\asyncio\proactor_events.py", line 54, in __repr__
    info.append('fd=%s' % self._sock.fileno())
  File "C:\Program Files\Python36\lib\asyncio\windows_utils.py", line 152, in fileno
    raise ValueError("I/O operatioon on closed pipe")
ValueError: I/O operatioon on closed pipe

How can I remove this error? stdin.close and wait seems not sufficient.

Solution

Note, that unlike in synchronous programming many asyncio functions are actually coroutines that should be awaited. See how wait() defined in documentation:

You should fix your code to await this coroutine:

async def test(exe):
  inst = await create_subprocess_exec(exe, stdin=PIPE, stdout=PIPE, stderr=STDOUT)

  data = await inst.stdout.readline()  # readline, for example, is also coroutine.
  print(data)

  await inst.wait()

You won't see any error now.

Answered By - Mikhail Gerasimov