使用方法创建类

Question

我写了一个名为car的类,其中包含属性model,year和speed.它还有3种方法,加速,制动,honk_horn.每次加速调用时我都试图增加5,但我无法让它工作.我在这做错了什么？

class Car:
    """Defines the Car class.
       Data attributes: model of type str
                        year of type int
                        speed of type float
    """

    def __init__(self, model, year, speed=0):
        """Creates new Car object with specified model, year, and speed"""
        self.model = model
        self.year = year
        self.speed = speed

    def accelerate(self):
        self.speed + 5 #everytime it is called

    def brake(self):
        if self.speed != 0: #If speed already zero don't minus 5
            self.speed - 5
        else:
            self.speed

    def honk_horn(self):
        print("{} goes 'beep beep'".format(self.model))

使用下面的测试我应该得到35,但我只得到30:

my_car = Car("Zastava", 2001, 30)
my_car.accelerate()
my_car.accelerate()
my_car.brake()
print(my_car.speed)

Answer 1

您没有为其分配值self.speed.您只需在不使用结果的情况下执行数学运算.

变更声明如下:

self.speed + 5 #everytime it is called

对此:

self.speed = self.speed + 5 #everytime it is called

或这个:

self.speed += 5 #everytime it is called