An Alternating Asynchronous Generator in Python

from asyncio import run, sleep



class AlternatingGenerator:

    def __init__(self, gen1, gen2):

        self.gen1 = gen1

        self.gen2 = gen2

        self.next = gen1



    def __aiter__(self):

        return self



    async def __anext__(self):



        # if we are done we both generators

        if not self.gen1 and not self.gen2:

            raise StopAsyncIteration



        try:

            # saving the current generator into a variable for later

            current = self.next



            # if the other genrerator is not null, alternating to it for the next iteration

            if self.next is self.gen1 and self.gen2:

                self.next = self.gen2

            elif self.next is self.gen2 and self.gen1:

                self.next = self.gen1



            # calling the generator of the current iteration and returning the next result

            return await anext(current)



        except StopAsyncIteration:



            # unsetting the generator that just finished

            if current is self.gen1:

                self.gen1 = None

            else:

                self.gen2 = None



            # recursive call, trying again with the other generator

            return await self.__anext__()







async def three():

    for i in range(3, 31, 10):

        await sleep(0.25)

        yield i





async def five():

    for i in range(5, 101, 10):

        await sleep(0.25)

        yield i



async def main():

    gen = AlternatingGenerator(three(), five())



    try:  # or just use "async for item in gen:"

        while True:

            print(await anext(gen))

    except StopAsyncIteration:

        pass



if __name__ == '__main__':

    run(main())

$ python alternating_generator.py 

3

5

13

15

23

25

35

45

55

65

75

85

95