用方法創建一個類

Question

我寫了一個名爲car的類，其屬性模型，年份和速度。它也有3種加速，制動，honk_horn的方法。每次調用加速時，我都會嘗試添加5，但我無法使其工作。我在這裏做錯了什麼？

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)) 

我應該使用下面的測試進行測試時得到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

你不self.speed分配一個值。你只是在不使用結果的情況下進行數學運算。

變化如下聲明：

self.speed + 5 #everytime it is called 

這樣：

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

或本：

self.speed += 5 #everytime it is called 

Answer 2

 self.speed + 5 #everytime it is called 

應該

 self.speed += 5 #everytime it is called 

當我加入的只是+

另外一個+ =而是你brake功能失常以類似的方式

Answer 3

變化self.speed + 5到self.speed = self.speed + 5 變化self.speed - 5到self.speed = self.speed - 5 應該工作