roundrobin.py

def roundrobin(pending):
    remaining = set(pending)

    index = 0
    while remaining:
        for requester in list(remaining):
            try:
                if process_success(requester, pending[requester][index]):
                    del pending[requester][index]
            except IndexError:
                remaining.remove(requester)
            else:
                index += 1