Why am I getting NotImplementedError with async and await on Windows?

Different event loops are implemented differently. Some of them have restrictions (sometimes OS-related). By default, Windows uses SelectorEventLoop and as you can see in doc:

SelectorEventLoop has the following limitations:

• SelectSelector is used to wait on socket events: it supports sockets and is limited to 512 sockets.
• loop.add_reader() and loop.add_writer() only accept socket handles (e.g. pipe file descriptors are not supported).
• Pipes are not supported, so the loop.connect_read_pipe() and loop.connect_write_pipe() methods are not implemented.
• Subprocesses are not supported, i.e. loop.subprocess_exec() and loop.subprocess_shell() methods are not implemented.

To run your code in Windows you can use alternative event loop available by default - ProactorEventLoop.

Replace line:

loop = asyncio.get_event_loop()

with this:

loop = asyncio.ProactorEventLoop()
asyncio.set_event_loop(loop)

Your code will work.

3.7.0 Python documentation handles this here: https://docs.python.org/3/library/asyncio-platforms.html#asyncio-windows-subprocess

Set the event loop policy if you are using Windows - then your code will work.

In your startup, change the unix-specific section:

cmds = [
    ['du', '-sh', '/Users/fredrik/Desktop'],
    ['du', '-sh', '/Users/fredrik'],
    ['du', '-sh', '/Users/fredrik/Pictures']
]

to handle Windows & Unix:

if 'win32' in sys.platform:
    # Windows specific event-loop policy & cmd
    asyncio.set_event_loop_policy(asyncio.WindowsProactorEventLoopPolicy())
    cmds = [['C:/Windows/system32/HOSTNAME.EXE']]
else:
    # Unix default event-loop policy & cmds
    cmds = [
        ['du', '-sh', '/Users/fredrik/Desktop'],
        ['du', '-sh', '/Users/fredrik'],
        ['du', '-sh', '/Users/fredrik/Pictures']
    ]