Python: AttributeError: 'Point' object has no attribute 'x'

Question

Traceback (most recent call last):
line 56, in <module>
    distanceToOne = point1.Distance(pointUser)
line 22, in Distance
    distance = math.sqrt((self.__x - toPoint.x)**2 +(self.__y - toPoint.y)**2 +(self.__z - toPoint.z)**2)
AttributeError: 'Point' object has no attribute 'x'

For some reason I keep getting the above error message whenever I get to: distanceToOne = point1.Distance(pointUser) after grabbing my three points to calculate the distance from.

Here is a better view if needed: http://pastie.org/private/vige6oaphkwestdemr5uw

Thanks in advance for your help!

import math
class Point(object):
    def __init__(self, x = 0, y = 0, z = 0, description = 'TBD'):
        self.__x = x
        self.__y = y
        self.__z = z
        self.__description = description

    def SetPoint(self, coords):
        self.__x = coords[0]
        self.__y = coords[1]
        self.__z = coords[2]

    def GetPoint(self):
        return [self.__x, self.__y, self.__z]
    PointCoords = property(GetPoint, SetPoint)

    def Distance(self, toPoint):
        toPoint.PointCoords[0]
        toPoint.PointCoords[1]
        toPoint.PointCoords[2]
        return math.sqrt(
            (self.__x - toPoint.x)**2 +
            (self.__y - toPoint.y)**2 +
            (self.__z - toPoint.z)**2)

    def SetDescription(self, description):
        self.__description = description

    def GetDescription(self):
        return self.__description
    PointDescription = property(GetDescription, SetDescription)

if __name__ == "__main__":
    print "Program 9: Demonstrate how to define a class"

    point2 = Point()
    point1 = Point(10, 54, 788, 'Ploto')
    point2.PointCoords = 77, 2, 205
    point2.PointDescription = 'Mars'
    doAnother = "y"
    while(doAnother == "y"):
        pointX = raw_input("Enter a X Number: ")
        pointY = raw_input("Enter a Y Number: ")
        pointZ = raw_input("Enter a Z Number: ")

        # Constructor - Represent the user's location
        pointUser = Point(pointX, pointY, pointZ, 'Sun')

        distanceToOne = point1.Distance(pointUser)
        distanceToTwo = point2.Distance(pointUser)

        # Comparing the two distances between the two to see which one is the closest
        if (distanceToOne > distanceToTwo):
            closest = point2
        else:
            closest = point1
            print ('You are closest to',closest.PointDescription(), 'which is located at ',closest.PointCoords())
        doAnother = raw_input("Do another (y/n)? ").lower()
    print ('Good Bye!')

Answer 1

The actual error is due to accessing toPoint.x, which doesn't exist because you have never defined it.

On a related note, prepending attributes with double underscores activates pythons name mangling feature. The actual attributes will still be publicly accessible at my_point._Point__x, my_point._Point__y, etc from outside the class.

As a matter of style, there does not seem to be any reason to use name mangling in this case. The intended use-case of this feature is to avoid clashes with inherited classes, it's not really about trying to make "private" variables (for that, the convention is to use a single underscore to indicate when an attribute is implementation detail).

In your case, I think you should just name (and access) the attributes normally x, y, etc. In python we don't normally write getters and setters for class members unless there is a special requirement to do so, because Python is not Java.