On Nov 19, 7:05 pm, Steven D'Aprano <st...@remove-this-
cybersource.com.au> wrote:
> If I want a mapping a <-> b, I generally just create a dict {a:b, b:a}.
> What is the advantages or disadvantages of your code over the simplicity
> of the dict approach?Well for one, you don't have to manually update the mapping from b -> a if ever the mapping from a -> b changes. With your method you have to write something like "d[a] = c; d[c] = a; del d[b]" instead of just "d[a] = c", "del d[d.pop(a)]" instead of just "del d[a]", etc. More significantly, your approach doesn't actually model a bijection since there's no distinction between keys (the domain) and values (the range). In other words, you lose information about which way is the forward mapping and which is the inverse mapping. Worse, d.keys() and d.values() would each give you the combination of your keys and values, neither of which would be right, and d.items() would also return twice as many elements as you expect with no way to distinguish which side of the mapping a given pair comes from. -- http://mail.python.org/mailman/listinfo/python-list
