python学习之路---类

• 一、创建和使用类
• • • 创建类
    • 根据类创建实例
• 二、使用类和实例
• • 1.给属性指定默认值
  • 2.修改属性的值
• 三、继承
• 总结

class dog:
    def __init__(self,name,age):
        self.name = name
        self.age = age
    def sit(self):
        print(f"{self.name} is sitting now")
    def roll_over(self):
        print(f"{self.name} rolled over!")

my_dog = dog('willie',6)
print(f"my dog's name is {my_dog.name}")
print(f"my dog's is {my_dog.age} years old")

修改实例的属性：
1、直接修改；
2、编写方法修改实例。

class Car:
    def __init__(self,make,model,year):
        self.make = make
        self.model = model
        self.year = year

    def get_descriptive_name(self):
        long_name = f"{self.year} {self.make} {self.model}"
        return long_name.title()

my_new_car = Car('audi','a4',2019)
print(my_new_car.get_descriptive_name())

创建实例时，有些属性不需要通过形参来定义，可以在_init_（）方法中指定默认值

class Car:
    def __init__(self, make, model, year):
        self.make = make
        self.model = model
        self.year = year
        self.odometer_reading = 0

    def get_descriptive_name(self):
        long_name = f"{self.year} {self.make} {self.model}"
        return long_name.title()

    def read_odometer(self):
        print(f"this car has {self.odometer_reading} miles on it")

my_new_car = Car('audi', 'a4', 2019)
print(my_new_car.get_descriptive_name())
my_new_car.read_odometer()

1：直接修改属性的值

my_new_car.odometer_reading = 23
my_new_car.read_odometer()

2：通过方法修改属性的值
在该类中添加此方法，通过方法修改属性的值。

    def update_odometer(self,mileage):
        self.odometer_reading = mileage

python中继承没有关键字，通过子类中的括号添加父类即可。

class ElectricCar(Car):
    def __init__(self,make,model,year):
        super().__init__(make,model,year)
        # 添加新的属性
        self.battery = Battery()

my_tesla = ElectricCar('tesla','model s',2019)
print(my_tesla.get_descriptive_name())
my_tesla.battery.describe_battery()
my_tesla.battery.get_range()

class Battery:
    def __init__(self,battery_size=75):
        self.battery_size = battery_size

    def describe_battery(self):
        print(f"this car has a {self.battery_size}-kwh battery")

    def get_range(self):
        if self.battery_size == 75:
            range = 260
        elif self.battery_size == 100:
            range = 315

        print(f"this car can go about {range} miles on a full charge.")

python类