请教，关于《Python从入门到实践》第九章 类 中的例子 electric_car一段代码的问题

照着书写了这段代码，出现了如下错误：

书上代码：

代码如下：
def get_range(self):
if self.battery_size == 70:
range = 240
elif self.battery_size == 85:
range = 270

    message = "This car can go approximately " + str(range)
    message += " miles on full charge."
    print(message)

请问书上这段是不是错了？

我自己对这方法进行了修改，加了个名为range的形参并赋值后，程序就可以运行了，不知道这样做是否是原书的本意？
def get_range(self, range=240):
if self.battery_size == 70:
range = 240
elif self.battery_size == 85:
range = 270

    message = "This car can go approximately " + str(range)
    message += " miles on full charge."
    print(message)

还一种修改的方法就是用else，代码如下：
def get_range(self):
if self.battery_size == 70:
range = 240
elif self.battery_size == 80:
range = 280
else:
range = 200
message = "This car can go approximately " + str(range)
message += " miles on full charge."
print(message)
这样也可运行

原因的话，自己猜测是通过赋值或者else完全定义了range，也不知道想得对不对，请各位坛友指教。

书上的写法完全没问题，你检查一下你自己的代码，下面是书上的

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 = 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 cant roll back an odometer!')
    def increment_odometer(self,miles):
        self.odometer_reading += miles
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
        elif self.battery_size == 85:
            range = 270

        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().__init__(make,model,year)
        self.battery = Battery()

from car import ElectricCar

my_tesla = ElectricCar('tesla','model s',2016)
print(my_tesla.get_descriptive_name())
my_tesla.battery.describe_battery()
my_tesla.battery.get_range()

2016 Tesla Model S
This car has a 70-kWh battery.
This car can go approximately 240 miles on a full charge

首先range是根据if条件进行创建变量。但是在built-in里面有一个range类，那么也就是说，不管你有没有定义range，这个执行都是对的。
只是执行的结果不同而已。最好是贴完整代码好看一些。