asyncio.as_completed(fs, *, loop=None, timeout=None) 
Return an iterator whose values, when waited for, are Future instances.
Raises asyncio.TimeoutError if the timeout occurs before all Futures are done.
Example:
for f in as_completed(fs):
    result = yield from f  # The 'yield from' may raise
    # Use result
 Note The futures f are not necessarily members of fs.