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Some additional thoughts for anyone else that comes across this issue.
Consider the case of a weakref proxy (the only proxy type in the stdlib): for that, you never want to serialise the proxy, you want to serialise the original object.
To correctly serialise a proxy object, you have to somehow ensure:
- the proxy gets serialised
- the target gets serialised
- the two get hooked up again at the far end
Now consider what happens if you have *two* proxies both pointing at the same target: how do you ensure that, when deserialised, both proxies still share a target?
In the general case, you can't - so pickle doesn't even try. Instead, serialising a proxy serialises the original object - if you want to do something else, you need to decide for yourself how to recreate the cross-references correctly on deserialisation.