spinner_yield.py

#!/usr/bin/env python3

# spinner_yield.py

# credits: Example by Luciano Ramalho inspired by
# Michele Simionato's multiprocessing example in the python-list:
# https://mail.python.org/pipermail/python-list/2009-February/538048.html

import asyncio
import itertools


@asyncio.coroutine  # <1>
def spin(msg):
    for char in itertools.cycle('|/-\\'):
        status = char + ' ' + msg
        print('\r' + status, end='', flush=True)
        try:
            yield from asyncio.sleep(.1)  # <2>
        except asyncio.CancelledError:  # <3>
            break
    print('\r', end='')


@asyncio.coroutine  # <4>
def slow_function():
    # pretend waiting a long time for I/O
    yield from asyncio.sleep(3)  # <5>
    return 42


@asyncio.coroutine  # <6>
def supervisor(loop):
    spinner = loop.create_task(spin('thinking!'))  # <7>
    print('spinner object:', spinner)  # <8>
    result = yield from slow_function()  # <9>
    spinner.cancel()  # <10>
    return result


def main():
    loop = asyncio.get_event_loop()  # <11>
    result = loop.run_until_complete(supervisor(loop))  # <12>
    loop.close()
    print('Answer:', result)


if __name__ == '__main__':
    main()