[Edu-sig] Reversing dictionaries, closures, permutations etc.

[Terry Hancock]

On Friday 23 January 2004 01:56 pm, Kirby Urner wrote:
> How to reverse a dictionary?  The dict class has no .reverse() method, which
> makes sense, as keys must be immutable so there's no guarantee the reverse
> is even valid (throwing an exception would be the way to go in this case).
>a straightforward way to do it in code would be:

Be aware also that the reverse (or inverse) may also be degenerate, unless
you have a strict 1:1 correspondence between keys and values.  There are
cases of use of course, and bear in mind that the inverse of the inverse of
dictionary is *guaranteed* to be 1:1.  I use something like this when I need
to have such a guarantee and want a reversible mapping.

Cheers,
Terry

--
Terry Hancock ( hancock at anansispaceworks.com )
Anansi Spaceworks  http://www.anansispaceworks.com