[Tutor] design of Point class

[Steven D'Aprano]

On Thu, 26 Aug 2010 07:29:42 am Gregory, Matthew wrote:

> I hope you'll suffer me one more question on this thread.  In
> thinking about creating other distance methods (as you suggest), how
> best to create a generic enough interface, so that ANY distance
> metric could be used.  It seems like coding the Point class with
> multiple distance methods is not very flexible, especially if you
> wanted to iterate over those methods for any two points, e.g.
>
> class Point(tuple):
>     def euclidean_distance(self, other):
>         ...
>     def manhattan_distance(self, other):
>         ...
>     def any_other_distance(self, other):
>         ...
>
> Would this be a place for a generic get_distance with a
> DistanceMetric subclass as a parameter, e.g.
>
> class DistanceMetric(object):
>     def distance(self, p1, p2):
>         assert 0, 'Must be defined in subclasses'
>
> class EuclideanDistMetric(DistanceMetric):
>     def distance(self, p1, p2):
>         ...
>
> class Point(tuple):
>     def get_distance(self, other, metric):
>         distance = metric.distance(self, other)
>         return distance


That could work, but it seems like a terribly heavyweight solution for a 
lightweight problem to me.

It doesn't save you any work -- you still have to code the distance 
method, but instead of creating a single method, you have to create an 
entire class. So it's more work.

I believe the simplest solution is to use the bound methods as first 
class functions:

pt = Point(23, 42)
# choose a distance 
if today == "Tuesday":
    dist = pt.manhattan_distance
else:
    dist = pt.euclidean_distance
for other in list_of_other_points:
    print(dist(other))



-- 
Steven D'Aprano