<与孩子一起学编程>第十四章

对象

1、什么是对象？具有属性和方法（能够对对象做的操作）的某个实例可以称为对象。如，一个球，属性有球的颜色，球的大小，球的重量，方法有球的运动方向；

2、属性和方法。如1中所述，属性很好理解，就是能够描述对象特征的一些变量，方法可以理解为一些代码块，这些代码块可以对对象完成一些操作，和我们平时讲的函数有些相似；

3、什么是类？对象的描述（将要让这个对象做什么实现什么功能）或蓝图称为一个类；

4、创建类的一个实例。类的定义只是写了一个框架，将有什么样的属性，将要实现什么样的功能，都是空谈，只有使用类来建立一个真正的对象，类才会发挥真正的作用，该对象就称为这个类的实例。

5、特殊方法__init__()和__str__()。只要创建该类的一个新实例，就要运行__init__()方法，该方法可以向实例的属性传递自己希望的值，完成初始化。__str__()可以按照自己的想法打印类中 的内容，

如：def __str__(self):

          msg = "Hi,I'm a "+self.size+" "+self.color+" ball!"

          return msg

6、多态。同一个方法，不同的行为。同一个函数名的方法，用在不同的类中，实现的功能不同，称为多态。

7、继承。向父类学习。父类有的属性和方法子类也同样有，子类还可以新增自身的属性和方法，提高代码的复用率。

如：class GameObject:

          def __init__(self,name):

               self.name = name

          def pickUp(self,player):

              pass

     class Coin(GameObject):#继承GameObject类

         def __init__(self,value):

              GameObject.__init__(self,"coin")#继承初始化方法并添加新的属性

              self.value = value

         def spend(self,buyer,seller):#添加新的方法

               pass

8、Python中的关键字pass可以作为一个占位符，一时半会想不起来写什么内容的时候，先占位这，这样函数方法模块不会报错


动手试一试
1、为BankAccount建立一个类定义。它应该有一些属性，包括账户名（一个字符串）、账号（一个字符串或整数）和余额（一个浮点数），
另外还要有一些方法显示余额、存钱和取钱'''

class BankAccount:
    def __init__(self,account_name,account_number):
        self.account_name = account_name
        self.account_number = account_number
        self.account_overage = 0.0
       
    def ShowOverage(self):
        print "The account balance is ",self.account_overage
       
    def Save(self,money):
        self.account_overage = self.account_overage + money
        print "You save ",money
        print "The new overage is ",self.account_overage
       
    def Withdrawal(self,money):
        if self.account_overage >= money:
            self.account_overage = self.account_overage - money
            print "You withdrawal ",money
            print "The new overage is ",self.account_overage
        else:
            print "You tried to withdrawal",money
            print "Your balance is",self.account_overage
            print "No enough funds"
           
myAccount = BankAccount("muyu", 123456)
print "Account name", myAccount.account_name
print "Account number", myAccount.account_number
myAccount.ShowOverage()

myAccount.Save(100)
myAccount.Withdrawal(20.5)
myAccount.Withdrawal(50)

2、建立一个可以挣利息的类，名为InterestAccount。这应当是BankAccount的一个子类（所以会继承BankAccount的属性和方法）。InternetAccount还
应当有一个对应利息率的属性，另外有一个方法来增加利息。为了力求简单，假设每年会调用一次addInternet()方法计算利息并更新余额'''
class BankAccount:
    def __init__(self,account_name,account_number):
        self.account_name = account_name
        self.account_number = account_number
        self.account_overage = 0.0
       
    def ShowOverage(self):
        print "The account balance is ",self.account_overage
       
    def Save(self,money):
        self.account_overage = self.account_overage + money
        print "You save ",money
        print "The new overage is ",self.account_overage
       
    def Withdrawal(self,money):
        if self.account_overage >= money:
            self.account_overage = self.account_overage - money
            print "You withdrawal ",money
            print "The new overage is ",self.account_overage
        else:
            print "You tried to withdrawal",money
            print "Your balance is",self.account_overage
            print "No enough funds"
           
class InterestAccount(BankAccount):
    def __init__(self, interest_rate):
        BankAccount.__init__(self, "muyu", 123456)#继承BankAccount类
        self.interest_rate = interest_rate
       
    def addInterest(self):
        interest = self.account_overage * self.interest_rate
        print "Your interest is",interest
        print "Your overall funds is",interest+self.account_overage
       
myAccount = InterestAccount(0.2)
myAccount.Save(100)
myAccount.Withdrawal(20.5)
myAccount.Withdrawal(50)
myAccount.addInterest()