Use of inheritance
The methods of the subclass are more and more complete than the methods of the parent class, otherwise the inheritance will not have much effect
class Animals(object):
def __init__(self, name, age):
self.name = name
self.age = age
def sleep(self):
print(self.name + '正在睡觉')
class Dog(Animals):
def bark(self):
print(self.name + '正在叫')
class Pig(Animals):
def eat(self):
print(self.name + '吃东西')
# Dog()调用__new__方法，在调用__init__方法
# 如果Dog里没有__new__方法，会查看父类是否重写了__new__方法
# 父类里也没有重写__new__方法，会查看父类的父类，找到了object
# 调用__init__方法，Dog类没有实现，会自动找Animals父类
dog1 = Dog('大黄', 18)
print(dog1.name) # 父类定义的属性，子类可以直接调用
dog1.sleep() # 父类定义的方法，子类也可以直接使用
dog1.bark()
pig1 = Pig('佩奇', 11)
pig1.sleep()
pig1.eat()
Characteristics of multiple inheritance
class A(object):
def demo_a(self):
print('我是A类里的demo_a方法')
def foo(self):
print('我是A类里的foo方法')
class B(object):
def demo_b(self):
print('我是B类里的demo_b方法')
def foo(self):
print('我是B类里的foo方法')
class C(A, B):
pass
c = C()
c.foo()
c.demo_a()
c.demo_b()
'''
我是A类里的foo方法
我是A类里的demo_a方法
我是B类里的demo_b方法
'''
class X(object):
def foo(self):
print('我是X类里的foo方法')
class Y(object):
pass
class Z(X):
pass
class M(Y):
def foo(self):
print('我是M类里的foo方法')
class N(Z, M):
pass
n = N()
n.foo() # 深度优先
print(N.__mro__) # __mro__属性，可以列出累继承的查找顺序
'''
我是X类里的foo方法
(<class '__main__.N'>, <class '__main__.Z'>, <class '__main__.X'>, <class '__main__.M'>, <class '__main__.Y'>, <class 'object'>)
'''
Inheritance characteristics of private attributes
Private properties and private methods are not inherited
class Animals(object):
__type = '动物'
def __init__(self, name, age):
self.name = name
self.age = age
self.__money = 1000
def __text(self):
print('我是Animals类里的私有方法__text')
class Pig(Animals):
def __demo(self):
print('我是Pig类里的私有方法__demo方法')
ma = Pig('小马', 18)
ma._Pig__demo() # 自己类里定义的方法，对象名._类名__方法名
ma._Animals__text() # 可以通过 对象名._父类名__方法名 调用父类的私有方法
# 私有属性和方法，子类不会继承
print(ma._Animals__money)
# 下面两个都会报错
# print(ma._Pig__money)
# ma._Pig__text()
Implementation of polymorphism
- Polymorphism is based on inheritance, the method of rewriting the parent class through the subclass
- To reach different subclass objects call the same parent method, get different results
- Improve code flexibility
class Person(object):
def __init__(self, name, age):
self.name = name
self.age = age
def sleep(self):
print(self.name + '正在睡觉')
class Student(Person):
def __init__(self, name, age, school):
# 子类在父类的基础上又添加自己新的属性
# 调用父类的两种方法
# 1. 父类名.方法名(self,参数列表)
# Person.__init__(self,name,age)
# 2. 使用super方法直接调用父类的方法。推荐使用第二种方法
super(Student, self).__init__(name, age)
self.school = school
def sleep(self):
print(self.name + '在课间休息的时候睡觉')
s = Student('小花', 3, '幼稚园')
s.sleep()# 小花在课间休息的时候睡觉
print(Student.__mro__)
# (<class '__main__.Student'>, <class '__main__.Person'>, <class 'object'>)
Use of polymorphism
class Dog(object):
def work(self):
print('狗正在工作')
class Policedog(Dog):
def work(self):
print('警犬正在攻击敌人')
class Blinddog(Dog):
def work(self):
print('导盲犬正在领路')
class Drugdog(Dog):
def work(self):
print('缉毒犬正在搜毒')
class Person(object):
def __init__(self,name):
self.name=name
self.dog = None
def work_with_dog(self):
if self.dog is not None and isinstance(self.dog,Dog):
self.dog.work()
p = Person('张三')
ad = Policedog()
p.dog = ad
p.work_with_dog()
bd = Blinddog()
p.dog = bd
p.work_with_dog()
cd = Drugdog()
p.dog = cd
p.work_with_dog()
'''
警犬正在攻击敌人
导盲犬正在领路
缉毒犬正在搜毒
'''
Object-oriented related methods
class Person(object):
def __init__(self, name, age):
self.name = name
self.age = age
class School(object):
pass
class Student(Person, School):
pass
p1 = Person('张三', 18)
p2 = Person('张三', 18)
s = Student('jack', 18)
# is 的本质是获取两个的内存 id(p1)==id(p2)
print(p1 is p2) # 身份运算符，用来判断是否是同一个对象
print(type(p1) == Person) # 获取的就是类对象
# s 这个对象是否由Student类创建的？
print(type(s) == Student) # True
print(type(s) == Person) # False
# isinstance 用来判断一个对象是否由指定的类（或父类）实例化出来的
print(isinstance(s, (Student, School))) # True
print(isinstance(s, Person)) # True
# issubclass 用来判断一个类是否是另一个类的子类
print(issubclass(Student, Person)) # True