Question

我在更广泛的python脚本中使用operator方法时遇到问题。为了缩小问题范围，我创建了以下示例代码。

class Car:
   def __init__(self, Name, Speed):
      self.Name = Name
      self.Speed = Speed
      self.PrintText()

   def PrintText(self):
      print("My %s runs %s km/h." % (self.Name, self.Speed))

   def GetName(self):
      return self.Name

   def GetSpeed(self):
      return self.Speed

   def __sub__(self, other):
      try: # Try with assumption that we have to deal with an instance of AnotherClass
         a = self.GetSpeed()
      except: # If it doesn't work let's assume we have to deal with a float
         a = self

      try: # Try with assumption that we have to deal with an instance of AnotherClass
         b = other.GetSpeed()
      except: # If it doesn't work let's assume we have to deal with a float
         b = other

      return a - b

Car1 = Car("VW", 200.0)
Car2 = Car("Trabant", 120.0)
print("")

Difference = Car1 - Car2
print("The speed difference is %g km/h." % Difference)
print("")

Difference = Car2 - 6.0
print("My %s is %g km/h faster than a pedestrian." % (Car2.GetName(), Difference))
print("")

Difference = 250.0 - Car1
print("I wish I had a car that is %g km/h faster than the %s." % (Difference, Car1.GetName()))

输出是：

My VW runs 200.0 km/h.
My Trabant runs 120.0 km/h.

The speed difference is 80 km/h.

My Trabant is 114 km/h faster than a pedestrian.

Traceback (most recent call last):
  File "test.py", line 41, in <module>
    Difference = 250.0 - Car1
TypeError: unsupported operand type(s) for -: 'float' and 'instance'

如何解决第一个对象是浮点数时出现的问题？

Answer 1

您需要使用反向操作数定义减法（代码本身已修复//您的问题，但可能需要更多清理）：

My VW runs 200.0 km/h.
My Trabant runs 120.0 km/h.

The speed difference is 80 km/h.

My Trabant is 114 km/h faster than a pedestrian.

I wish I had a car that is 50 km/h faster than the VW.

现在你的输出：

const Button& GetObjectBelowMouse(int xMousePos, int yMousePos) // This would be equavalent to your Connect type
{
    // all buttons would be your container of buttons / GUI objects.
    for( const auto& button : allButtons)
    {
        // top,bottom,left,right would be the bounding rectangle that encapsulates the coordinates of the object
        if( (xMousePos > button.left && xMousePos < button.right ) && (yMousePos > button.bottom && yMousePos < buttom.top))
        {
            return button;
        }
    }
    // in this case we have a different constructor that creates a "empty" button that has no function
    return Button(NO_OBJECT);
}

// the usage would be something like

int main()
{
    /* 
        .. create button, set it's possition, etc
    */

    // Option 1
    if(GetObjectBelowMouse(mouse.x, mouse.y).type != NO_OBJECT)
    {
        // Do whatever you want, you know that the user has clicked a valid object
        button.Foo();
    }

    // Option 2
    GetObjectBelowMouse(mouse.x, mouse.y).Foo(); // You know that every button has a foo object, and that NO_OBJECT has a foo that does nothing, so you don't need to compare if it is NO_OBJECT or not.
}

Answer 2

对于您的具体问题并不是真正的答案，但将实际的速度减去速度，而不是汽车会更简单，更简洁>到速度。只需car1.Speed() - car2.Speed()或car2.Speed() - 6.0即可。否则你会创建自己的问题。

作为附注，我还建议您遵循Python样式指南https://www.python.org/dev/peps/pep-0008/

尝试在Python中使用运算符方法时出现类型错误

2 个答案: