proof-of-concept async subprocess file tail

c.py

#!/usr/bin/python3

import asyncio
import aiofiles
import textwrap


consumer = textwrap.dedent(
    """
    for i in {1..5}; do
      echo line $i
      sleep 1
    done
    """)


async def main():
    async with aiofiles.open('p', 'w') as p:
        await p.write(consumer)

    async with aiofiles.open('o.txt', 'w') as o:
        print('Starting subprocess')
        proc = await asyncio.create_subprocess_exec('bash', './p', stdout=o)

        print('Tailing file')
        async with aiofiles.open('o.txt', 'r') as f:
            while proc.returncode is None:
                async for line in f:
                    print('Line: {}'.format(line))

        print('Awating subprocess')
        await proc.wait()


loop = asyncio.get_event_loop()
loop.run_until_complete(main())
print('Closing')
loop.close()