内容概要
- 面向对象的三大特征
- 继承的属性查找顺序
- super()和mro()列表
- 多态与多态性
内容详细
继承(重要)
1. 什么是继承？
# 继承就是新建类的一种方式，新建的类我们称为子类或者叫派生类，被继承的类我们称为父类或者基类
# 子类可以使用父类中的属性或者方法
2. 为什么要用继承？
类解决了对象与对象之间的代码冗余问题
继承解决的是类与类之间的代码冗余问题
3. 如何使用继承？
新式类：继承了object类的子子孙孙类都是新式类
经典类：没有继承了object类的子子孙孙类都是经典类
# 新式类和经典类只有在python2中区分
类的继承
# 以学生选课系统为例
# 父类，公共类
class People():
school = 'SH'
def __init__(self, name, age, gender):
self.name = name
self.age = age
self.gender = gender
# 学生类
class Student(People):
def __init__(self, name, age, gender, course=None):
if course is None:
course = []
People.__init__(self, name, age, gender)
self.courses = course
def choose_course(self, course):
self.courses.append(course)
print('%s 选课成功 %s' % (self.name, self.courses))
stu = Student('ly', 19, 'male')
# teacher类
class Teacher(People):
def __init__(self, name, age, gender, level):
self.level = level
People.__init__(self, name, age, gender)
def score(self, stu_obj, score):
stu_obj.score = score # 给学生打分
print('%s给%s打了%s分' % (self.name, stu_obj.name, score))
tea = Teacher('ly', 19, 'male', 10)
print(tea.name)
print(tea.level)
单继承下属性查找
class Foo:
def f1(self):
print('Foo.f1')
def f2(self):
#
print('Foo.f2')
self.f1()
class Bar(Foo):
def f1(self):
print('Bar.f1')
obj = Bar() # {}
obj.f2()
# 练习
class Foo:
def __f1(self): # _Foo__f1()
print('Foo.f1')
def f2(self):
#
print('Foo.f2')
self.__f1() # _Foo__f1()
class Bar(Foo):
def __f1(self): # # _Bar__f1()
print('Bar.f1')
obj = Bar() # {}
obj.f2()
多继承下的属性查找
# 新式类：按照广度优先查询
# 经典类：按照深度优先查询
class A(object):
def test(self):
print('from A')
class B(A):
# def test(self):
# print('from B')
pass
class C(A):
# def test(self):
# print('from C')
pass
class D(B):
# def test(self):
# print('from D')
pass
class E(C):
# def test(self):
# print('from E')
pass
class F(D, E):
# def test(self):
# print('from F')
pass
f1 = F()
f1.test()
super()和mro列表
class People():
school = 'SH'
def __init__(self, name, age, gender):
self.name = name
self.age = age
self.gender = gender
class Teacher(People):
def __init__(self, name, age, gender, level):
self.level = level
super().__init__(name, age, gender) # super的使用
# mro列表练习1
class A:
def test(self):
print('from A.test')
super().test()
class B:
def test(self):
print('from B')
class C(A, B):
pass
c = C()
c.test()
# mro列表练习2
class B:
def test(self):
print('B---->test')
def aaa(self):
print('B---->aaa')
class A:
def test(self):
print('A---->test')
super().aaa()
class C(A, B):
def aaa(self):
print('C----->aaa')
c = A()
# c.test() # 打印结果:
print(A.mro())
多态与多态性
1. 什么是多态
水：液态水，固态水，气态水
动物：人，猪，狗，猫 ...
# 抽象类： 抽象类只能被继承，不能被实例化
class Animal(metaclass=abc.ABCMeta):
@abc.abstractmethod # 该方法已经是抽象方法了
def speak(self): pass
@abc.abstractmethod
def login(self):pass
class People(Animal):
def speak(self):
# print('嗷嗷嗷')
pass
def login(self):
pass
class Pig(Animal):
def speak(self):
print('哼哼哼')
class Dog(Animal):
def speak(self):
print('汪汪汪')
obj = People()
obj.speak()
# 多态练习
class Pig():
def speak(self):
print('哼哼哼')
class Dog():
def speak(self):
print('汪汪汪')
class Txt():
def speak(self):
print('Txt')
obj = People()
obj1 = Pig()
obj2 = Dog()
obj3 = Txt()
# 多态带来的特性：在不用考虑对象数据类型的情况下，直接调用对应的函数
def animal(animal):
return animal.speak()
animal(obj)
animal(obj1)
animal(obj2)
animal(obj3)
# 父类限制子类的行为
class Animal():
def speak(self):
raise Exception("必须实现speak方法")