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Python类定义和类继承详解

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Jun 10, 2016 pm 03:13 PM

python class definition Class inheritance

一、类定义：

1 2	`class` `<类名>:` `<语句>`

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类实例化后，可以使用其属性，实际上，创建一个类之后，可以通过类名访问其属性
如果直接使用类名修改其属性，那么将直接影响到已经实例化的对象

类的私有属性：
__private_attrs 两个下划线开头，声明该属性为私有，不能在类地外部被使用或直接访问
在类内部的方法中使用时 self.__private_attrs

类的方法
在类地内部，使用def关键字可以为类定义一个方法，与一般函数定义不同，类方法必须包含参数self,且为第一个参数

私有的类方法
__private_method 两个下划线开头，声明该方法为私有方法，不能在类地外部调用
在类的内部调用slef.__private_methods
类的专有方法：
__init__ 构造函数，在生成对象时调用
__del__ 析构函数，释放对象时使用
__repr__ 打印，转换
__setitem__按照索引赋值
__getitem__按照索引获取值
__len__获得长度
__cmp__比较运算
__call__函数调用

__add__加运算
__sub__减运算
__mul__乘运算
__div__除运算
__mod__求余运算
__pow__称方
示例:

#类定义 
class people: 
  #定义基本属性 
  name = ''
  age = 0 
  #定义私有属性,私有属性在类外部无法直接进行访问 
  __weight = 0 
  #定义构造方法 
  def __init__(self,n,a,w): 
    self.name = n 
    self.age = a 
    self.__weight = w 
  def speak(self): 
    print("%s is speaking: I am %d years old" %(self.name,self.age)) 
  
  
p = people('tom',10,30) 
p.speak() 

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二、继承类定义：

1.单继承

class <类名>(父类名)
  <语句>
eg.
class childbook(book)
  age = 10

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2.类的多重继承

1 2	`class` `类名(父类1,父类2,....,父类n)` `<语句1>`

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需要注意圆括号中父类的顺序，若是父类中有相同的方法名，而在子类使用时未指定，python从左至右搜索,即方法在子类中未找到时，从左到右查找父类中是否包含方法

#另一个类，多重继承之前的准备 
class speaker(): 
  topic = ''
  name = ''
  def __init__(self,n,t): 
    self.name = n 
    self.topic = t 
  def speak(self): 
    print("I am %s,I am a speaker!My topic is %s"%(self.name,self.topic)) 
  
#多重继承 
class sample(speaker,student): 
  a =''
  def __init__(self,n,a,w,g,t): 
    student.__init__(self,n,a,w,g) 
    speaker.__init__(self,n,t) 
  
test = sample("Tim",25,80,4,"Python") 
test.speak()#方法名同，默认调用的是在括号中排前地父类的方法 

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类方法的覆写——子类覆盖掉父类的方法
def 方法名与父类一致
若是在方法中要使用到父类方法父类名.方法名

若是将类放到了模块中

使用时

1 2	`import A` `l = A.类()`

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以上三段程序的执行结果:

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