coroutine - 示例

 分享流畅的python一书, coroutine 章节中的出租车仿真的例子.

 from  collections import namedtuple
 import queue
 import random
 Event = namedtuple('Event', 'time process action')

 def taxi_simu(ident, trips, start_t = ):
     time = yield Event(start_t, ident, 'get out of garage')
     for i in range(trips):
         time = yield Event(time, ident, 'pick up passenger')
         time = yield Event(time, ident, 'passenger arrive destination')

     yield Event(time, ident, 'off duty, going home')

 class Emulator(object):

     def __init__(self, proc_mapping):
         self.events = queue.PriorityQueue()        #  保存排定事件的 PriorityQueue 对象，按时间正向排序。
         self.process = dict(proc_mapping)          #  获取的 procs_map 参数是一个字典（或其他映射），可是又从中构建一个字典，创建本地副本，
                                                    #  因为在仿真过程中，出租车回家后会从 self.procs 属性中移除，而我们不想修改用户传入的对象
     '''
     优先队列是离散事件仿真系统的基础构件：创建事件的顺序不定，放入这种队列之后，可以按照各个事件排定的时间顺序取出。
     '''

     def comupte_duration(self, previous_action):
         if 'get out of garage' in previous_action:
             return random.randint(,)
         elif 'pick up passenger' in previous_action:
             return random.randint(,)
         elif 'passenger arrive destination' in previous_action:
             return random.randint(,)
         else:
             return
     def run(self, end_time):
         for _, process in sorted(self.process.items()):    #  使用 sorted 函数获取 self.procs 中按键排序的元素；用不到键，因此赋值给 _。
             first_event = next(process)                    #  调用 next(proc) 预激各个协程，向前执行到第一个 yield 表达式，做好接收数据的准备。产出一个 Event 对象。
             self.events.put(first_event)                   #  把各个事件添加到 self.events 属性表示的 PriorityQueue 对象中。

         simu_time =                                       #  把 sim_time 变量（仿真钟）归零
         while simu_time < end_time:
             if self.events.empty():                        #  如果队列中没有未完成的事件，退出主循环
                 print('empty events queue, all events done')
                 break

             current_event = self.events.get()              #  获取优先队列中 time 属性最小的 Event 对象；这是当前事件（current_event）
             simu_time, process_id, previous_action = current_event       # 拆包 Event 对象中的数据。这一行代码会更新仿真钟 sim_time，对应于事件发生时的时间。
                                                                          # 这通常是离散事件仿真：每次循环时仿真钟不会以固定的量推进，而是根据各个事件持续的时间推进
             print('Taxi : ', process_id, process_id * ' ', current_event)   # 显示 Event 对象，指明是哪辆出租车，并根据出租车的编号缩进
             actived_process = self.process[process_id]                    # 从 self.procs 字典中获取表示当前活动的出租车的协程
             next_time = simu_time + self.comupte_duration(previous_action)
             try:
                 next_event = actived_process.send(next_time)      #  把计算得到的时间发给出租车协程。协程会产出下一个事件（next_event），或者抛出 StopIteration 异常（完成时）
             except StopIteration:
                 del self.process[process_id]                     # 如果抛出了 StopIteration 异常，从 self.procs 字典中删除那个协程
             else:
                 self.events.put(next_event)                      # 否则，把 next_event 放入队列中
         else:
             msg = '=== end of simulation time : {} events are pending ==='
             print(msg.format(self.events.qsize()))               #     如果循环由于仿真时间到了而退出，显示待完成的事件数量（有时可能碰巧是零, 如 endtime 足够大，就不有 event pending, 都会处理完)

 if __name__ == '__main__':
     taxi_num =
     DEPARTURE_INTERVAL =
     end_time =
     taxis = {i: taxi_simu(i, (i+)*, i*DEPARTURE_INTERVAL)
                     for i in range(taxi_num)}

     simu = Emulator(taxis)
     simu.run(end_time)

 '''
 OUTPUT,

     Taxi :    Event(time=, process=, action='get out of garage')
     Taxi :    Event(time=, process=, action='pick up passenger')
     Taxi :     Event(time=, process=, action='get out of garage')
     Taxi :     Event(time=, process=, action='pick up passenger')
     Taxi :      Event(time=, process=, action='get out of garage')
     Taxi :      Event(time=, process=, action='pick up passenger')
     Taxi :       Event(time=, process=, action='get out of garage')
     Taxi :       Event(time=, process=, action='pick up passenger')
     Taxi :     Event(time=, process=, action='passenger arrive destination')
     Taxi :        Event(time=, process=, action='get out of garage')
     Taxi :     Event(time=, process=, action='pick up passenger')
     Taxi :        Event(time=, process=, action='pick up passenger')
     Taxi :       Event(time=, process=, action='passenger arrive destination')
     Taxi :       Event(time=, process=, action='pick up passenger')
     Taxi :    Event(time=, process=, action='passenger arrive destination')
     Taxi :    Event(time=, process=, action='pick up passenger')
     Taxi :       Event(time=, process=, action='passenger arrive destination')
     Taxi :     Event(time=, process=, action='passenger arrive destination')
     Taxi :      Event(time=, process=, action='passenger arrive destination')
     Taxi :       Event(time=, process=, action='pick up passenger')
     Taxi :      Event(time=, process=, action='pick up passenger')
     Taxi :     Event(time=, process=, action='pick up passenger')
     Taxi :        Event(time=, process=, action='passenger arrive destination')
     Taxi :        Event(time=, process=, action='pick up passenger')
     Taxi :       Event(time=, process=, action='passenger arrive destination')
     Taxi :       Event(time=, process=, action='pick up passenger')
     Taxi :    Event(time=, process=, action='passenger arrive destination')
     Taxi :        Event(time=, process=, action='passenger arrive destination')
     Taxi :    Event(time=, process=, action='off duty, going home')
     Taxi :        Event(time=, process=, action='pick up passenger')
     Taxi :       Event(time=, process=, action='passenger arrive destination')
     Taxi :       Event(time=, process=, action='pick up passenger')
     Taxi :      Event(time=, process=, action='passenger arrive destination')
     Taxi :     Event(time=, process=, action='passenger arrive destination')
     Taxi :        Event(time=, process=, action='passenger arrive destination')
     Taxi :     Event(time=, process=, action='pick up passenger')
     Taxi :      Event(time=, process=, action='pick up passenger')
     Taxi :        Event(time=, process=, action='pick up passenger')
     Taxi :       Event(time=, process=, action='passenger arrive destination')
     Taxi :       Event(time=, process=, action='pick up passenger')
     Taxi :     Event(time=, process=, action='passenger arrive destination')
     Taxi :        Event(time=, process=, action='passenger arrive destination')
     Taxi :     Event(time=, process=, action='off duty, going home')
     Taxi :        Event(time=, process=, action='pick up passenger')
     Taxi :      Event(time=, process=, action='passenger arrive destination')
     Taxi :      Event(time=, process=, action='pick up passenger')
     Taxi :       Event(time=, process=, action='passenger arrive destination')
     Taxi :       Event(time=, process=, action='pick up passenger')
     Taxi :        Event(time=, process=, action='passenger arrive destination')
     Taxi :        Event(time=, process=, action='pick up passenger')
     Taxi :      Event(time=, process=, action='passenger arrive destination')
     Taxi :      Event(time=, process=, action='pick up passenger')
     Taxi :       Event(time=, process=, action='passenger arrive destination')
     Taxi :       Event(time=, process=, action='pick up passenger')
     Taxi :        Event(time=, process=, action='passenger arrive destination')
     Taxi :        Event(time=, process=, action='pick up passenger')
     Taxi :       Event(time=, process=, action='passenger arrive destination')
     Taxi :       Event(time=, process=, action='off duty, going home')
     Taxi :      Event(time=, process=, action='passenger arrive destination')
     Taxi :      Event(time=, process=, action='pick up passenger')
     Taxi :        Event(time=, process=, action='passenger arrive destination')
     Taxi :      Event(time=, process=, action='passenger arrive destination')
     Taxi :        Event(time=, process=, action='pick up passenger')
     Taxi :      Event(time=, process=, action='off duty, going home')
     Taxi :        Event(time=, process=, action='passenger arrive destination')
     Taxi :        Event(time=, process=, action='pick up passenger')
     Taxi :        Event(time=, process=, action='passenger arrive destination')
     Taxi :        Event(time=, process=, action='pick up passenger')
     Taxi :        Event(time=, process=, action='passenger arrive destination')
     Taxi :        Event(time=, process=, action='off duty, going home')
     empty events queue, all events done

 '''