Check if variable is defined in the superclass or subclass

Question

This is just academic. Consider the following example:

class Shape():
    def __init__(self, x, y):
        self.x = x
        self.y = y
    
    def position(self):
        return self.x, self.y


class Rectangle(Shape):
    def __init__(self, x, y, height, width):
        #super().__init__(x, y)  # OK
        self.x = x  # not OK!
        self.y = y  # not OK!
        self.height = height
        self.width = width

r1 = Rectangle(1, 2, 3, 4)

If I asked someone to implement the class Rectangle, and they implemented with the "not OK" statements (instead of the with the "OK" statement as they should), then r1.x would be an attribute of Rectangle instead of Shape. Is there a way I can check if r1.x is a member of the Rectangle class or of the Shape class? Essentially, I want to make sure the initialization of the super class is being run, and no unnecessary new attributes are being created.