Wayne Werner wrote:
> class Point2D(PointND):
> def __init__(self, x = 0, y = 0):
> super(Point2D, self).__init__([x,y])
> self.x = 0
> self.y = 0
>
> though you wouldn't be able to directly modify the values, or you'll
> lose the distance function. You'd have to create setter functions, and as
> such should rename x and y to _x and _y, to indicate that sure you *can*
> touch
> these, but really you shouldn't.
>
> For the 3d, you'd just add a z param, although to really generalize your
> ND class you could do this instead:
>
> class PointND(object):
> def __init__(self, x=0, y=0, z=0, a_list=None):
> if a_list is not None:
> self.a_list = a_list[:]
> self.x = x
> self.y = y
> self.z = z
>
> def coords(self):
> return [self.x, self.y, self.z] + self.a_list
> ...
>
> Then your subclass takes less effort:
>
> class Point2D(PointND):
> def __init__(self, x=0, y=0):
> super(Point2D, self).__init__(x,y)
>
> and this allows you to access point.x, point.y, and point.z directly.
>
> Of course you could also subclass list with ND and just use descriptors
> for self[0], self[1], and self[2]:
> http://users.rcn.com/python/download/Descriptor.htm
Thanks all for good suggestions. I'm intrigued by the idea of subclassing list
(suggested by both Bob and Wayne) and using x, y and z as descriptors to the
elements in the list. Obviously, it's important that the descriptors (x,y,z)
stay in sync with the list itself so that:
>>> p = PointND(1,2,3)
>>> p.x = 10
>>> p
[10,2,3]
>From what I understood of the link Wayne sent, I should be able to use __set__
>to create this relationship between the labels and the list, but I'm totally
>lost on how to do this. It seems like x,y,z need to be instances of
>descriptor objects who have values that are associated with the list.
In the mean time, I've overridden __setattr__ to enforce this, but it looks a
bit crufty. Any further suggestions are most welcome.
class PointND(list):
def __init__(self, *a_list):
super(PointND, self).__init__(a_list)
if len(self) <= 3:
self.x = self[0]
if len(self) >= 2 and len(self) <= 3:
self.y = self[1]
if len(self) == 3:
self.z = self[2]
def __setattr__(self, attr, value):
if attr in ('x', 'y', 'z'):
self.__dict__[attr] = value
if attr == 'x':
self[0] = value
elif attr == 'y':
self[1] = value
else:
self[2] = value
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