On Sat, 09 Feb 2008 13:51:34 -0800, Magdoll wrote:
> Is there a cleaner way to do this example:
>
> d = {('a','b'): 10, ('a','c'): 20, ('b','c'): 30}
>
> The key is always a pair (x,y), but d[(x,y)] should have the same result
> as d[(y,x)]. So either I would have to store both d[(x,y)] and d[(y,x)]
> (unncessary extra space?)
Worse than the extra space is the near certainty of d[(x,y)] and d[(y,x)]
getting out of sync.
> or write something like:
>
> if x <= y: return d[(x,y)]
> else: return d[(y,x)]
Arggh, scattering all those tests throughout your code is too much like
hard work!
> I'm not familiar with python enough, so I want to know whether these are
> my only choices....
Oh no. Here's a good one:
class PairDict(dict):
def __getitem__(self, key):
if key[1] < key[0]: key = (key[1], key[0])
return super(PairDict, self).__getitem__(key)
and here it is in use:
>>> d = PairDict([((1,2), 5), ((3,4), 10)])
>>> d[(1,2)]
5
>>> d[(2,1)]
5
--
Steven
--
http://mail.python.org/mailman/listinfo/python-list
