Subpar

task.py

import heapq

class Task:
    def __init__(self, time):
        self.time = time

    def __lt__(self, other):
        return self.time < other.time

    def __repr__(self):
        return f'Task({self.time})'

    def spawned(self):
        '''Yield further tasks after run completes.'''
        if False:
            yield

    def run(self):
        '''Called at the scheduled time.'''
        return


class PrintTask(Task):
    def __init__(self, time, msg):
        self.time = time
        self.msg = msg

    def __repr__(self):
        return 'PrintTask({}, {})'.format(self.time, repr(self.msg))

    def run(self):
        print(self.msg)


class RecurrentTask(Task):
    def __repr__(self):
        return f'RecurrentTask({self.time})'

    def spawned(self):
        yield RecurrentTask(self.time + 1)

def run_tasks(tasks):
    pool = list(tasks)
    heapq.heapify(pool)
    while pool:
        task = heapq.heappop(pool)
        task.run()
        for new_task in task.spawned():
            heapq.heappush(pool, new_task)
        yield task

if __name__ == '__main__':
# Schedule some tasks
    tasks = [PrintTask(5, 'It is now time=5'),
            RecurrentTask(1),
            PrintTask(10, 'Final message'),
            ]
    print("Starting with tasks:")
    for task in tasks:
        print('\t' + str(task))
    print()
    for i, x in enumerate(run_tasks(tasks)):
        print("Ended:", x)
        if i > 20:
            print("... and so on")
            break