dict: retrieve the original key by key

[Christoph Groth]

Dear python experts,

I use a huge python dictionary where the values are lists of that
dictionary's keys (yes, a graph).  Each key is thus referenced several
times.

As the keys are rather large objects, I would like to save memory by
re-using key objects wherever possible, instead of having several equal
objects in memory.

There does not seem to be a way to retrieve the original key from a
python dictionary.  Is there a technical reason for this?  (Other than
that such functionality was not considered to be useful enough.)

What I will probably do now is store (key, real_value) as values in my
dictionary.  Is there a better solution?

thanks,
Christoph