text: 
  """
    Name     : c12_88_simpy_02.py
    Book     : Python for Finance (2nd ed.)
    Publisher: Packt Publishing Ltd. 
    Author   : Yuxing Yan
    Date     : 6/6/2017
    email    : yany@canisius.edu
               paulyxy@hotmail.com
  """
  
  import simpy
  def clock(env, name, tick):
       while True:
           print(name, env.now)
           yield env.timeout(tick)
  
  env = simpy.Environment()
  env.process(clock(env, 'fast', 0.5))
  env.process(clock(env, 'slow', 1))
  env.run(until=2)
  