Martin,

Sorry, I don't follow. I realise that the refcounts will be different;
but pickling an object should surely be independent of the refcount as
there is no need to include the refcount in the output?

What other way (using pickle or not) can I convert a generic immutable
Python object to a string to use as a key in external storage?

Currently the documentation points out that the output may be different
between pickle and cPickle which implies that the output will be
consistent for a single module.

If pickle is not required to produce consistent output for the same
input (and refcount isn't really part of the input in this case; it is 
a side issue) than can this be documented?