python中 _、__、__xx__()区别及使用场景

class Test:
 def __init__(self, foo):
  self.__foo = foo  # 私有属性

 # 定义私有函数，外界不可以直接访问，但是可以通过【_类名__函数名】去调用私有函数
 def __bar(self):
  print(self.__foo)
  print('__bar')

def main():
 """
 test = Test('hello')
 # AttributeError: 'Test' object has no attribute '__bar'
 test.__bar()
 # AttributeError: 'Test' object has no attribute '__foo'
 print(test.__foo)
 """
 
 # 使用以下这种方式就可以在类的外部调用类的私有属性与方法
 test._Test__bar()
 print(test._Test__foo)

if __name__ == "__main__":
 main()

import time

class Clock(object):
 """数字时钟"""

 def __init__(self, hour=0, minute=0, second=0):
  """初始化方法

  :param hour: 时
  :param minute: 分
  :param second: 秒
  """
  self._hour = hour
  self._minute = minute
  self._second = second

 def run(self):
  """走字"""
  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 __str__(self):
  """显示时间"""
  return '%02d:%02d:%02d' %(self._hour, self._minute, self._second)


def main():
 clock = Clock(23, 59, 58)
 while True:
  print(clock)
  time.sleep(1)
  clock.run()

if __name__ == '__main__':
 main()