[docs] bug in asyncio-subprocess documentation web pages

[Antonio Cacho]

Hi
There is a bug In these asyncio-subprocess web pages:
     https://docs.python.org/3.8/library/asyncio-subprocess.html
     https://docs.python.org/3.7/library/asyncio-subprocess.html
The bug occurs in the first example program. It lacks the conditional 
use of WindowsProactorEventLoopPolicy from the sys package.
The erroneous code and the tested working code are attached.
I couldn't find this bug in the documenting issue tracker, but I doubt 
no one has stumbled on it before, and I was in hurry.
Cheers,
     Antonio Jose Cacho






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-------------- next part --------------
import asyncio

async def run(cmd):
    proc = await asyncio.create_subprocess_shell(
        cmd,
        stdout=asyncio.subprocess.PIPE,
        stderr=asyncio.subprocess.PIPE)

    stdout, stderr = await proc.communicate()

    print(f'[{cmd!r} exited with {proc.returncode}]')
    if stdout:
        print(f'[stdout]\n{stdout.decode()}')
    if stderr:
        print(f'[stderr]\n{stderr.decode()}')

asyncio.run(run('ls /zzz'))
-------------- next part --------------

import asyncio
import sys

async def run(cmd):
    proc = await asyncio.create_subprocess_shell(
        cmd,
        stdout=asyncio.subprocess.PIPE,
        stderr=asyncio.subprocess.PIPE)

    stdout, stderr = await proc.communicate()

    print(f'[{cmd!r} exited with {proc.returncode}]')
    if stdout:
        print(f'[stdout]\n{stdout.decode()}')
    if stderr:
        print(f'[stderr]\n{stderr.decode()}')

if sys.platform == "win32":
    asyncio.set_event_loop_policy(
        asyncio.WindowsProactorEventLoopPolicy())

asyncio.run(run('dir ..'))