9.3.6 模拟实物
模拟较复杂的物件(如电动汽车)时,需要解决一些有趣的问题。续航里程是电瓶的属性还是汽车的属性呢?如果我们只需描述一辆汽车,那么将方法get_range() 放在Battery 类中也许是合适的;但如果要描述一家汽车制造商的整个产品线,也许应该将方法get_range() 移到ElectricCar 类中。在这种情况下,get_range() 依然根据电瓶容量来确定续航里程,但报告的是一款汽车的续航里程。我们也可以这样做:将方法get_range() 还留在Battery 类中,但向它传递一个参数,如car_model ;在这种情况下,方法get_range() 将根据电瓶容量和汽车型号报告续航里程。
该怎么写呢?
class Car():
def __init__(self,make,model,year):
self.make = make
self.model = model
self.year = year
self.odometer_reading = 100
def describe(self):
long_name = str(self.year) + ' ' + self.make + ' ' + self.model
return long_name.title()
def read_odometer(self):
print("this car has " + str(self.odometer_reading) + " miles on it.")
def update_odometer(self,mileage):
if mileage >=self.odometer_reading:
self.odometer_reading = mileage
else:
print("you can't roll back an odometer!")
def increment(self,miles):
self.odometer_reading = self.odometer_reading + miles
my_new_car = Car('audi','a4','2016')
print(my_new_car.describe())
#电动车类
class Battery():
def __init__(self,battery_size=70):
self.battery_size = battery_size
def describe_battery(self):
print("this car has a " + str(self.battery_size) + "-kwh battery")
def get_range(self):
if self.battery_size == 70:
range = 240
message = "this car can go approximately " + str(range)
message += " miles on a full charge."
print(message)
class ElectricCar(Car):
def __init__(self,make,model,year):
super(ElectricCar, self).__init__(make,model,year)
self.battery = Battery()
my_tesla = ElectricCar('tesla','model s',2016)
print(my_tesla.describe())
my_tesla.battery.describe_battery()
my_tesla.battery.get_range()