[Python-Dev] The memo of pickle

[Tim Peters]

[Tim]
> The object's id() (address) is the key.  Else only hashable objects
> could be pickled.

[Greg Ewing]
> Hmmm, I see.
>
> It occurs to me that what you really want here is a special
> kind of dictionary that uses "is" instead of "==" to compare
> key values.

Possibly.  The *effect* of that could be gotten via a wrapper object, like

class KeyViaId:
    def __init__(self, obj):
        self.obj = obj
    def __hash__(self):
        return hash(id(self.obj))
    def __eq__(self, other):
        return self.obj is other.obj

but if Martin is worried about two-tuple sizes, he's not going to fall in
love with that.

> Or is that what was meant by an "identity dictionary"?

Guido asked, but if Martin answered that question I haven't seen it yet.