UnboundLocalError: local variable 'range' referenced before assignment

Posted 2021-05-23 乘风破浪会有时，直挂云帆济沧海

1. 报错信息

UnboundLocalError: local variable \'range\' referenced before assignment

2. 代码

class Car():
    """一次模拟汽车的简单尝试"""
    def __init__(self, make, model, year):
        """初始化描述汽车的属性"""
        self.make = make
        self.model = model
        self.year = year
        self.odometer_reading = 0

    def get_descriptive_name(self):
        """返回整洁的描述性信息"""
        long_name = str(self.year) + \' \' + self.make + \' \' + self.model
        return long_name.title()

    def read_odometer(self):
        """打印一条指出汽车里程的消息"""
        print("This car has " + str(self.odometer_reading) + " miles on it.")

    def update_odometer(self, mileage):
        """将里程表读数设置为指定值"""
        self.odometer_reading = mileage
        """
        将里程表读数设置为指定的值，
        禁止将里程表读数往回调
        """
        if mileage >= self.odometer_reading:
            self.odometer_reading = mileage
        else:
            print("You can\'t roll back an odometer!")

    def increment_odometer(self, miles):
        """将里程表读数增加指定的量"""
        self.odometer_reading += miles

# my_used_car = Car(\'subaru\', \'outback\', 2013)
# print(my_used_car.get_descriptive_name())
#
# my_used_car.update_odometer(23500)
# my_used_car.read_odometer()
#
# my_used_car.increment_odometer(100)
# my_used_car.read_odometer()

# my_new_car = Car(\'audi\', \'a4\', 2016)
# print(my_new_car.get_descriptive_name())
# my_new_car.update_odometer(23)
# # my_new_car.odometer_reading = 23
# my_new_car.read_odometer()

class Battery():
    """一次模拟电动汽车的属性"""
    def __init__(self, battery_size = 60):
        """初始化电瓶属性"""
        self.battery_size = battery_size


    def describle_battery(self):
        """打印一天描述电瓶容量的消息"""
        print("This car has a " + str(self.battery_size) + " -kWh battery.")

    def get_range(self):
        """打印一条描述电瓶续航里程的消息"""
        # range = 200
        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):
    """模拟电动汽车的独特之处"""
    def __init__(self, make, model, year):
        """初始化父类的属性，在初始化电动汽车特有属性"""
        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.describle_battery()
my_tesla.battery.get_range( )

　　

3. 解决方法

在get_range()方法中先定义一个range变量，然后进行逻辑运算

    def get_range(self):
        """打印一条描述电瓶续航里程的消息"""
        range = 200 # 先定义变量，后进行运算
        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)

　　

4. 执行结果

D:\\python编程：从入门到实践\\venv\\Scripts\\python.exe D:/python编程：从入门到实践/my_electric_car.py
2016 Tesla Model S
This car has a 60 -kWh battery.
This car can go approximately 200 miles on a full charge.

Process finished with exit code 0