yield from

def has_yield_from_bug():
    class MyGen:
        def __init__(self):
            self.send_args = None
        def __iter__(self):
            return self
        def __next__(self):
            print('next')
            return 42
        def send(self, *what):
            print('send function')
            self.send_args = what
            return None
    def yield_from_gen(gen):
        print('before yield')
        yield from gen
        #_iter = iter(gen)
        #while True:
        # try:
        #        item = next(_iter)
        #        s = yield item
        # if s is not None and hasattr(gen, 'send'):
        #            gen.send(s)
        # except StopIteration:
        # break
        print('after yield')
    value = (1, 2, 3)
    gen = MyGen()

    coro = yield_from_gen(gen)
    print('before next')
    next(coro)
    print('after next , before send')
    coro.send(value)
    print('after send')
    return gen.send_args != (value,)
_YIELD_FROM_BUG = has_yield_from_bug()
print(_YIELD_FROM_BUG)

运行结果为：

[Cambox@laptop ~]$ python34 python-test/test.py
before next
before yield
next
after next , before send
send function
after send
False