mytid = yield GetTid() or mytid = (yield GetTid())

I am learning coroutine fromwww.dabeaz.com/coroutines/pyos5.py and read the following code:

class GetTid(SystemCall):
    def handle(self):
        self.task.sendval = self.task.tid
        self.sched.schedule(self.task)


def foo():
    mytid = yield GetTid()
    for i in range(10):
        print("I'm foo", mytid)
        yield

Reference to mytid = yield GetTid(),

I really confused about this,

is it mytid = (yield GetTid())?

The author use an instance as a variable to receive data. Is it a good pattern?

from mytid = yield GetTid() or mytid = (yield GetTid())