Question

我刚写了这堂课：

class PhysicsObject:
    "An object that is physically simulated. Has velocity, position, and orientation."

    def __init__(self):
        self.velocity=Vector(0,0)
        self.position=Vector(0,0)
        self.heading=0
        #This gives a direction vector that represents the direction the physics object is facing
        self.forward=property(fget=lambda self: Vector(1,0).rotate(self.heading))
        #This gives an integer that represents how fast the object is moving in the direction it's facing
        self.fwdspeed=property(fget=lambda self: self.velocity.dot(self.forward))
        self.mass=1

为了测试它，我写了一些代码：

myphysobj=PhysicsObject()
myphysobj.velocity=Vector(15,5)
print("Position:",myphysobj.position,"Facing:",myphysobj.forward,"Forward Speed:",myphysobj.fwdspeed)

我希望结果可以是这样的：

Position: (0,0) Facing: (0,0) Forward Speed: 5

然而，我反而得到了

Position: (0,0) Facing: <property object at 0x02AB2150> Forward Speed: <property object at 0x02AB2180>

据我了解，将属性设置为property(fget=myfunc)的结果应该在访问该属性时给出myfunc()的结果。相反，它似乎给了我属性对象本身。我误解了property()是如何使用的，还是我犯了一个更微妙的错误？

Answer 1

property是descriptor，描述符应该直接在类上定义，而不是在实例上定义。

class PhysicsObject:
  forward = property(fget=lambda self: Vector(1,0).rotate(self.heading))
  fwdspeed = property(fget=lambda self: self.velocity.dot(self.forward))

  def __init__(...):
     ...

Python属性访问会导致属性对象本身

1 个答案: