Python中怎么定义类和对象

# -*- coding:utf-8 -*-
#! python3
class dvd:
  def __init__(self,name,price,state):
    self.name=name;
    self.price=price
    self.state=state
  def __str__(self):
    stat='已借出';
    if self.state==1:
      stat='未借出'
    return '名称：《%s》 单价:%d 状态:%s'%(self.name,self.price,stat)
class DVDManager:
  #存储 多个dvds 每一个元素 都是一个DVD
  dvds=[]
  def init(self):
    self.dvds.append(dvd('光辉岁月',10,0));
    self.dvds.append(dvd('绅士', 5, 1));
    self.dvds.append(dvd('海阔天空', 11, 1));
  def Menu(self):
    self.init()
    while(True):
      print('1.查询所有DVD')
      print('2.增加DVD')
      print('3.借出DVD')
      print('4.归还DVD')
      print('5.退出')
      choose=int(input('请选择：'));
      if choose==1:
        self.showAllDVD();
      elif choose==2:
        self.insertDVD();
      elif choose==3:
        self.jiechuDVD();
      elif choose==4:
        self.rollBackDVD();
      elif choose==5:
        print('5.谢谢使用')
        break;
  def showAllDVD(self):
    for d in self.dvds:
      print(str(d))
  def jiechuDVD(self):
    name = input('请输入DVD的名称：')
    ret = self.checkDVD(name);
    if ret != None:
      if ret.state==0:
        print('dvd 已经借出去了')
        #return;
      else:
        days=int(input('请输入借出天数：'))
        ret.state = 0;
        print('借出 %d 天，应还利息%d '%(days,ret.price*days))
    else:
      print('DVD 不存在！')
  def rollBackDVD(self):
    name = input('请输入归还DVD的名称：')
    ret = self.checkDVD(name);
    if ret == None:
      print('DVD 不存在！')
    else:
      if ret.state == 1:
        print('dvd 未借出！')
      else:
        days= int(input('请输入借出去了多少天？'))
        y_money=ret.price * days
        print('借出 %d 天，应还利息%d ' % (days, y_money))
        money=0;
        while True:
          money= int(input('请输入金额:'))
          #带学生完成..
          if money<y_money:
            print('不够！')
          else:
            break;
        if money>=y_money:
          print('找零：%d'%(money-y_money));
        ret.state=1;
        print('归还成功！')
  def insertDVD(self):
    name = input('请输入DVD的名称：')
    ret= self.checkDVD(name);
    if ret != None:
      print('DVD 已经存在！')
    else:
      price=int(input('请输入价格：'))
      new_dvd=dvd(name,price,1);
      self.dvds.append(new_dvd)
      print('存放成功！')
  def checkDVD(self,name):
    for d in self.dvds:
      if d.name==name:
        return d;#返回当前对象-->内存地址
    else:
      return None;
manager= DVDManager();
manager.Menu();

# -*- coding:utf-8 -*-
#! python3
class pet:
  def kanbing(self):
    print('给宠物看病。。')
class Car(pet):
  def kanbing(self):
    print('给猫咪看病 吃药，吃小黄鱼..')
class Dog(pet):
  def kanbing(self):
    print('给狗狗看病 输液 吃骨头....')
class bird(pet):
  def kanbing(self):
    print('看小鸟看病 拔罐 吃虫子... ')
class pig(pet):
  def kanbing(self):
    print('给小猪看病 针灸 吃猪粮... ')
class ShouVet:
  def JiuZhen(self,pet):
    print('兽医出诊..给宠物看病...')
    pet.kanbing();
class person:
  def kanbing(self):
    print('给人类看病 望闻问切 多喝水..')
dingdang=Car();
kala=Dog();
huangli=bird();
peiqi=pig()
bianque=person()
syi=ShouVet();
syi.JiuZhen(dingdang);
syi.JiuZhen(kala);
syi.JiuZhen(huangli);
syi.JiuZhen(peiqi);
syi.JiuZhen(bianque)

# -*- coding:utf-8 -*-
#! python3
class Operation(object):
  '''
  四则运算的父类,接收用户输入的数值
  '''
  def __init__(self, number1=0, number2=0):
    self.num1 = number1
    self.num2 = number2
  def GetResult(self):
    pass
  pass
#加法运算类
class OperationAdd(Operation):
  def GetResult(self):
    return self.num1 + self.num2
#减法运算类
class OperationSub(Operation):
  def GetResult(self):
    return self.num1 - self.num2
#乘法运算类
class OperationMul(Operation):
  def GetResult(self):
    return self.num1 * self.num2
#除法运算类
class OperationDiv(Operation):
  def GetResult(self):
    if self.num2 == 0:
      return '除数不能为0 '
    return 1.0*self.num1 / self.num2
#其他操作符类
class OperationUndef(Operation):
  def GetResult(self):
    return '操作符错误'
#简单工厂类
class OperationFactory(object):
  def choose_oper(self,ch):
    if ch == '+':
      return OperationAdd()
    elif ch == '-':
      return OperationSub()
    elif ch == '*':
      return OperationMul()
    elif ch == '/':
      return OperationDiv()
    else:
      return OperationUndef()
if __name__ == "__main__":
  ch = ''
  while not ch == 'q':
    num1 = input('请输入第一个数值: ')
    oper = str(input('请输入一个四则运算符: '))
    num2 = input('请输入第二个数值: ')
    # Operation(num1,num2)
    OF = OperationFactory()
    oper_obj = OF.choose_oper(oper)
    oper_obj.num1 = num1
    oper_obj.num2 = num2
    print('运算结果为: ',oper_obj.GetResult())