On Fri, 08 Apr 2005 10:33:53 -0600, Matthew Thorley wrote: > I must say I am *very* suprised that python does not have a way to look > up what key is pointing to a given object--without scanning the whole > list that is.
Assuming fairly optimal data structures, nothing is free. Python chooses not to have bi-directional dicts built in. A good reason for this is that it is easy to build a two-way dict out of two one-way dicts, and there's no obvious way to build a "built-in" two-way dict that is any more efficient than that. Python chooses to allow all objects potentially to be dict keys, which has overhead vs. an implementation such as that in Perl that only allows strings. Either of those is tolerable ultimately, though I do prefer Python's approach as I key things on objects all the time. It's all a matter of tradeoffs. Building all the dicts as two-way in memory consumes twice the memory and twice the processor power for a lot of situations where the second direction isn't used, so *on average* that's not a good tradeoff. Even though Python doesn't have a built-in way, it is easy to write your own class that interoperates transparently, and there are many ones you can grab off the 'net, even given to you in this thread :-) -- http://mail.python.org/mailman/listinfo/python-list
