面向对象2

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（了解）

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")