python设计一个计时器

from time import sleep
import os

class Clock(object):
  """计时器"""

  def __init__(self, hour=0, minute=0, second=0):
      self._hour = hour
      self._minute = minute
      self._second = second
  
  def run(self):
      self._second += 1
      if self._second == 60:
          self._second = 0
          self._minute += 1
          if self._minute == 60:
              self._minute = 0
              self._hour += 1
              if self._hour == 24:
                  self._hour = 0
  
  def show(self):
      return ('%02d:%02d:%02d' %(self._hour, self._minute, self._second))


def main():
  clock = Clock(23, 59, 59)
  while True:
      os.system('clear')
      print(clock.show())
      sleep(1)
      clock.run()

      
if __name__ == "__main__":
  try:
      main()
  except KeyboardInterrupt:
      exit()