gen.py 文件源码

def convert_yielded(yielded):
    """Convert a yielded object into a `.Future`.

    The default implementation accepts lists, dictionaries, and Futures.

    If the `~functools.singledispatch` library is available, this function
    may be extended to support additional types. For example::

        @convert_yielded.register(asyncio.Future)
        def _(asyncio_future):
            return tornado.platform.asyncio.to_tornado_future(asyncio_future)

    .. versionadded:: 4.1
    """
    # Lists and dicts containing YieldPoints were handled earlier.
    if isinstance(yielded, (list, dict)):
        return multi(yielded)
    elif is_future(yielded):
        return yielded
    elif isawaitable(yielded):
        return _wrap_awaitable(yielded)
    else:
        raise BadYieldError("yielded unknown object %r" % (yielded,))