new_contents: #!/usr/bin/python3
  
  import os
  import sys
  
  def rabbitNum(time, rate):
      ''' Calculate the number of rabbit pairs after some time periods
          at the reproduction rate.
          Assume 1 young pair at period 1 and rabbits live forever.'''
      assert time >= 1
      assert rate >= 1
  
      pre, cur = 0, 1
      for i in range(1, time):
          pre, cur = cur, pre * rate + cur
      return cur
  
  def printRabbit(time, rate):
      ''' Output number of rabbits to a format '''
      print("t={:3}\tr={:3}\tnum={}".format(time, rate, rabbitNum(time, rate)))
  
  if __name__ == "__main__":
      printRabbit(1, 100)
      printRabbit(5,3)
      printRabbit(5,1)
      printRabbit(33,2)
  
subject: Add counting rabbit