Implementing Tuples and Lists in the isinstance Function in Python 2.7

Question

I am trying to accept tuple and list as object types in an __add__ method in Python. Please see the following code:

class Point(object):
'''A point on a grid at location x, y'''
    def __init__(self, x, y):
        self.X = x
        self.Y = y

    def __str__(self):
        return "X=" + str(self.X) + "Y=" + str(self.Y)

    def __add__(self, other):
        if not isinstance(other, (Point, list, tuple)):
            raise TypeError("Must be of type Point, list, or tuple")
        x = self.X + other.X
        y = self.Y + other.Y
        return Point(x, y)

p1 = Point(5, 10)

print p1 + [3.5, 6]

The error I get when running it in the Python interpreter is:

AttributeError: 'list' object has no attribute 'X'

I simply cannot figure our why this isn't working. This is homework for a college course and I have very little experience with Python. I know that the isinstance function in Python can accept a tuple of type objects, so I am not sure what element I am missing for tuple and list objects to be accepted. I feel like this is something really simple I am just not picking up on.

Answer 1

If you want to be able to add lists or tuples, change your __add__ method:

def __add__(self, other):
    if not isinstance(other, (Point, list, tuple)):
        raise TypeError("Must be of type Point, list, or tuple")
    if isinstance(other, (list, tuple)):
        other = Point(other[0], other[1])
    x = self.X + other.X
    y = self.Y + other.Y
    return Point(x, y)

Otherwise, you'd have to add another Point object, not a list. In that case, just tweak your last line:

print p1 + Point(3.5, 6)

Answer 2

As simple as error you got says: the list object in python (or probably in any language does not have x or y attributes). You must handle list (and tuple also) case separately