ParisGabriel：Python全栈工程师（0基础到精通）教程 第二十七课（类变量、方法、继承、覆盖）

# -*- coding:utf-8 -*-

# 类变量


class Human:
    total_count = 0  # 类变量

    def __init__(self, name):
        print(name, ‘对象被创建‘)


print(Human.total_count)  # 0
h1 = Human("zhang")
print(h1.total_count)  # 0　用此类实例访问类变量
h1.total_count = 100  # 为对象添加实例变量
print(h1.total_count)  # 100　　优先访问实例变量
print(Human.total_count)  # 0　访问类变量


class Human:
    total_count = 0  # 类变量

    def __init__(self, name):
        print(name, ‘对象被创建‘)


h1 = Human("zhang")
print(Human.total_count)  # 0
h1.__class__.total_count = 100  # 为类添加修改实例变量
print(h1.total_count)  # 100　　间接访问类变量
print(Human.total_count)  # 100　访问类变量


# 类变量的应用　　用类变量记录实例个数


class Human:
    total_count = 0  # 类变量

    def __init__(self, name):
        print(name, ‘对象被创建‘)
        self.__class__.total_count += 1  # 每次创建对象调用__init__　类变量加1

    def __del__(self):
        self.__class__.total_count += 1  # 每次析构对象后类变量减1


h1 = Human("zhang")
print("此时Human对象的个数是", Human.total_count)  # 1
L = []
L.append(Human("li"))
L.append(Human("zhao"))
print("此时Human对象的个数是", Human.total_count)  # 3
del h1
L.pop()
print("此时Human对象的个数是", Human.total_count)  # 1

>>> class Dog:
...     ‘‘‘这是小动物‘‘‘
... 
>>> help(Dog)

>>> Dog.__doc__
‘这是小动物‘
>>> 

class Human:
    # 以下列表限制此类对象只能有这两个属性　防止出错
    __slots__ = ["name", "age"]

    def __init__(self, name, age):
        self.name, self.age = name, age


h1 = Human("Ta", 15)
print(h1.age)  # 15
h1.Age = 18  # 区分大小写　出错　没有Age属性，也不允许有
print(h1.age)  # 15

# 类方法的使用

class A:
    v = 0

    @classmethod
    def get_v(cls):  # cls 用来绑定调用此方法的类
        return cls.v  # 访问类变量

    @classmethod
    def set_v(cls, value):
        cls.v = value


print(A.get_v())  # 0
A.set_v(100)
print(A.get_v())  # 100
a1 = A()  # 创建实例
print("a1.get_v=", a1.get_v)  # 100
a1.set_v(200)
print("a1.get_v=", a1.get_v)  # 200
print("A.get_v=", A.get_v)  # 200

# 静态方法

class A:
    @staticmethod
    def myadd(a, b):
        return a + b


print(A.myadd(100, 200))  # 300
a = A()  # 创建实例
print(a.myadd(300, 400))  # 700


# def myadd(a, b):  # 和静态方法结果一样
#     return a + b


# class A:
#     pass


# print(A.myadd(100, 200))  # 300
# a = A()  # 创建实例
# print(a.myadd(300, 400))  # 700

# 单继承用法


class Human:  # 人类的共性
    def say(srlf, what):
        print("说：", what)

    def walk(self, distance):  # 走路
        print("走了", distance, "公里")


class Student(Human):  # 继承
    # def say(srlf, what):
    #     print("说：", what)

    # def walk(self, distance):  # 走路
    #     print("走了", distance, "公里")

    def study(self, subject):  # 派生
        print("学习", subject)


class Teacher(Student):
    def teach(self, subject):  # 派生
        print("教", subject)


h1 = Human()
h1.say("哈哈")
h1.walk(500)


s1 = Student()
s1.walk(4)
s1.say("666")
s1.study("python")


T1 = Teacher()
T1.walk(4)
T1.say("666")
T1.teach("python")
T1.study("Java")

# 覆盖 override


class A:
    def works(self):
        print("A.works被调用")


class B(A):
    ‘‘‘B继承A类‘‘‘
    def works(self):
        print("B.works被调用")


b = B()
b.works()  # B.works被调用
# B.works　覆盖　A.works　优先调用子类　
# A派生B  B继承A

# 子类对象显示调用基类（被覆盖）方法的方式：
#   基类.方法名（实例， 实际调用参数）

A.works(b)  # 用类名显示调用，　A.works被调用

# 用super函数返回的对象调用父类的覆盖方法

class A:
    def works(self):
        print("A.works被调用")


class B(A):
    ‘‘‘B继承A类‘‘‘
    def works(self):
        print("B.works被调用")

    def super_works(self):
        self.works()  # B.works被调用
        super(B, self).works()  # A.works被调用
        super().works()  # A.works被调用

b = B()
b.works()  # B.works被调用
super(B, b).works()  # A.works被调用


b = B()
b.super_works()  # B.works被调用

# 用super函数调用父类的覆盖__init__初始化方法


class Human:
    def __init__(self, n, a):
        self. name, self.age = n, a
        print("Human类的 __init__　方法被调用")

    def infos(self):
        print("name:", self.name)
        print("age:", self.age)


class Student(Human):
    def __init__(self, n, a, s=0):
        super().__init__(n, a)  # 用siper　调用父类的__init__方法
        self.score = s  # 添加成绩属性
        print("Student类的 __init__　方法被调用")

    def info(self):
        super().infos()  # 调用父类的方法
        print("name:", self.name)
        print("age:", self.age)
        print("score:", self.score)  # 不调用父类的方法也不会出错　但是尽量不要用


s1 = Student("小张", 20)
s1.infos()