如何在产量中扩展元组?

我试图在一个yield语句中展开一个元组,但我得到了一个 SyntaxError .这是可能的,还是 *

下面是一个示例:

class Inner(object):
    def __init__(self):
        self._vals = {'a': 1,
                      'b': 2,
                      'c': 3,
                      'd': 4}

    def __iter__(self):
        for key, val in self._vals.items():
            yield key, val

class Outer(object):
    def __init__(self):
        self._morevals = {"foo": Inner(),
                          "bar": Inner()}

    def __iter__(self):
        for key, moreval in self._morevals.items():
            for val in moreval:
                yield key, *val    # !!! <--- This is where the error is

object_under_test = Outer()

for outer_key, inner_key, inner_value in object_under_test:
    print("{} {} {}".format(outer_key, inner_key, inner_value))

    # Want:
    # foo a 1
    # foo b 2
    # foo c 3
    # foo d 4
    # bar a 1
    # bar b 2
    # bar c 3
    # bar d 4

相反,我得到了这个错误:

    yield key, *val
               ^
SyntaxError: invalid syntax