futures.py 文件源码

def __init__(self, *, loop=None):
        """Initialize the future.

        The optional event_loop argument allows to explicitly set the event
        loop object used by the future. If it's not provided, the future uses
        the default event loop.
        """
        if loop is None:
            self._loop = events.get_event_loop()      # ????
        else:
            self._loop = loop

        self._callbacks = []     # ??

        if self._loop.get_debug():
            self._source_traceback = traceback.extract_stack(sys._getframe(1))