crorotine experiment implemented with yield

yield_coro.py

class Dispatcher:
    def __init__(self):
        self.tasks = []

    def reg_task(self, t):
        self.tasks.append(t)

    def run(self):
        while len(self.tasks):
            for t in self.tasks:
                try:
                    t.send(None)
                except StopIteration as e:
                    self.tasks.remove(t)
                    if not self.tasks:
                        break

    def switch(self):
        yield
    def stop(self):
        self.tasks.clear()


d = Dispatcher()


def th1():
    while True:
        print('step1')
        yield from d.switch()
        print('step2')


def th2_loop10():
    count = 5
    while count:
        count -= 1
        yield from d.switch()
    print('many ticks passed, time to go back')
    return 10


def th3():
    while True:
        print('thread3_step1')
        yield from d.switch()
        print('thread3_step2:  wait th2')
        r = yield from th2_loop10()
        print('thread3_step3: th2 returned ' + str(r))
        d.stop()


def stop_early(tick):
    while tick:
        tick -= 1
        yield from d.switch()
    print('task finished')

if __name__ == '__main__':
    d.reg_task(th1())
    d.reg_task(th3())
    d.reg_task(stop_early(3))
    d.run()