Btw, regarding compatibility:  The docs say " The pickle serialization format is guaranteed to be backwards compatible across Python releases."

I take this to mean the serialization format itself.  I don't think there is a broader guarantee that pickles generated by one version can be read by another, since objects can change their internal representation, types can even disappear or change.

In that sense, pickles made by 2.7 can be read by 3.2, in the sense that they will correctly return an error when they can't construct a 'str' object.

If I misunderstand things, then at least I think that the pickle documentation should be made clearer, that not only is the protocol supposed to be read, but also that entire pickles should always be readable _and_ instantiatable, by future versions