Doing set operation on non-hashable objects

[5lvqbwl02 at sneakemail.com]

Hi,

I'm writing an application which is structured roughly as follows:

"db" is a dict, where the values are also dicts.
A function searches through db and returns a list of values, each of
which is a dict as described above.
I need to perform set operations on these lists (intersection and
union)
However the objects themselves are not hashable, and therefore can't
be in a set, because they are dicts.
I'm not sure how large each set will be, but the point is I'm trying
to avoid anything looking like an O(n^2) algorithm, so I can't just
use naive double-looping to check for intersection/union on a pair of
lists.

The only way I can think of to do this right is to hash the dicts by
freezing them, turning them all into tuples, which can then be
hashed.  But this is a problem because more dicts might be nested
inside.  At any rate, I'd need to thaw them out when I'm done and turn
them back into dicts, which seems complicated and annoying, and all
this leads me to believe there is a better way.

What I really need is a set of pointers, so at the end of the
operation I have the actual objects pointed to.  Can I somehow use the
object IDs as set elements, then recreate a list with the actual
objects they point to?

How do you get the object back from an ID in python?

thanks
Michael