"""Support for running coroutines in parallel with staggered start times."""__all__='staggered_race',from .importlocksfrom .importtasksfrom .importtaskgroupsasyncdefstaggered_race(coro_fns,delay,*,loop=None):"""Run coroutines with staggered start times and take the first to finish.    This method takes an iterable of coroutine functions. The first one is    started immediately. From then on, whenever the immediately preceding one    fails (raises an exception), or when *delay* seconds has passed, the next    coroutine is started. This continues until one of the coroutines complete    successfully, in which case all others are cancelled, or until all    coroutines fail.    The coroutines provided should be well-behaved in the following way:    * They should only ``return`` if completed successfully.    * They should always raise an exception if they did not complete      successfully. In particular, if they handle cancellation, they should      probably reraise, like this::        try:            # do work        except asyncio.CancelledError:            # undo partially completed work            raise    Args:        coro_fns: an iterable of coroutine functions, i.e. callables that            return a coroutine object when called. Use ``functools.partial`` or            lambdas to pass arguments.        delay: amount of time, in seconds, between starting coroutines. If            ``None``, the coroutines will run sequentially.        loop: the event loop to use.    Returns:        tuple *(winner_result, winner_index, exceptions)* where        - *winner_result*: the result of the winning coroutine, or ``None``          if no coroutines won.        - *winner_index*: the index of the winning coroutine in          ``coro_fns``, or ``None`` if no coroutines won. If the winning          coroutine may return None on success, *winner_index* can be used          to definitively determine whether any coroutine won.        - *exceptions*: list of exceptions returned by the coroutines.          ``len(exceptions)`` is equal to the number of coroutines actually          started, and the order is the same as in ``coro_fns``. The winning          coroutine's entry is ``None``.    """# TODO: when we have aiter() and anext(), allow async iterables in coro_fns.winner_result=Nonewinner_index=Noneexceptions= []class_Done(Exception):passasyncdefrun_one_coro(this_index,coro_fn,this_failed):try:result=awaitcoro_fn()except (SystemExit,KeyboardInterrupt):raiseexceptBaseExceptionase:exceptions[this_index]=ethis_failed.set()# Kickstart the next coroutineelse:# Store winner's resultsnonlocalwinner_index,winner_result# There could be more than one winnerwinner_index=this_indexwinner_result=resultraise_Donetry:asyncwithtaskgroups.TaskGroup()astg:forthis_index,coro_fninenumerate(coro_fns):this_failed=locks.Event()exceptions.append(None)tg.create_task(run_one_coro(this_index,coro_fn,this_failed))try:awaittasks.wait_for(this_failed.wait(),delay)exceptTimeoutError:pass    except*_Done:passreturnwinner_result,winner_index,exceptions

cherry_picker de929f353c413459834a2a37b2d9b0240673d874 3.12