point class help

[r]

I am hacking up a point class but having problems with how to properly
overload some methods. in the __add__, __sub__, __iadd__, __isub__, I
want to have the option of passing an instance or a container(list,
tuple) like

>>> p1 = Point2d(10,10)
>>> p1 += (10,10)
>>> p1
Point2d(20,20)
>>>
>>> p2 = Point2d(10,10)
>>> p2 += p1
>>> p2
Point2d(30,30)


here is what i have, it would seem stupid to use a conditional in each
method like this...

def method(self, other):
    if isinstance(other, Point2d):
        x, y = origin.x, origin.y
    else:
        x, y = origin[0], origin[1]
    #modify self.x & self.y with x&y

there must be a way to get the x, y with reusable code, i am not about
to have this conditional under every method call, What am i missing
here?


class Point2d():
    def __init__(self, x, y=None):
        if type(x) == tuple:
            self.x = x[0]
            self.y = x[1]
        else:
            self.x = x
            self.y = y

    def __str__(self):
        return 'Point2d(%f, %f)' %(self.x, self.y)

    def __add__(self, other):
        if isinstance(other, Point2d):
            x, y = origin.x, origin.y
        else:
            x, y = origin[0], origin[1]
        return (self.x+x, self.y+y)

    def __sub__(self, other):
        pass

    def __iadd__(self, other): #+=
        pass

    def __isub__(self, other): #-=
        pass

any ideas?