Function gather

Lib/asyncio/tasks.py:768–908

Return a future aggregating results from the given coroutines/futures. Coroutines will be wrapped in a future and scheduled in the event loop. They will not necessarily be scheduled in the same order as passed in. All futures must share the same event loop. If all the tasks are

(*coros_or_futures, return_exceptions=False)

def gather(*coros_or_futures, return_exceptions=False):
    """Return a future aggregating results from the given coroutines/futures.

    Coroutines will be wrapped in a future and scheduled in the event
    loop. They will not necessarily be scheduled in the same order as
    passed in.

    All futures must share the same event loop.  If all the tasks are
    done successfully, the returned future's result is the list of
    results (in the order of the original sequence, not necessarily
    the order of results arrival).  If *return_exceptions* is True,
    exceptions in the tasks are treated the same as successful
    results, and gathered in the result list; otherwise, the first
    raised exception will be immediately propagated to the returned
    future.

    Cancellation: if the outer Future is cancelled, all children (that
    have not completed yet) are also cancelled.  If any child is
    cancelled, this is treated as if it raised CancelledError --
    the outer Future is *not* cancelled in this case.  (This is to
    prevent the cancellation of one child to cause other children to
    be cancelled.)

    If *return_exceptions* is False, cancelling gather() after it
    has been marked done won't cancel any submitted awaitables.
    For instance, gather can be marked done after propagating an
    exception to the caller, therefore, calling ``gather.cancel()``
    after catching an exception (raised by one of the awaitables) from
    gather won't cancel any other awaitables.
    """
    if not coros_or_futures:
        loop = events.get_event_loop()
        outer = loop.create_future()
        outer.set_result([])
        return outer

    loop = events._get_running_loop()
    if loop is not None:
        cur_task = current_task(loop)
    else:
        cur_task = None

    def _done_callback(fut, cur_task=cur_task):
        nonlocal nfinished
        nfinished += 1

        if cur_task is not None:
            futures.future_discard_from_awaited_by(fut, cur_task)

        if outer is None or outer.done():
            if not fut.cancelled():
                # Mark exception retrieved.
                fut.exception()
            return

        if not return_exceptions:
            if fut.cancelled():
                # Check if 'fut' is cancelled first, as