I have a situation where an object in the ORM performs some calculations 
and other assorted checks.  One of these situations is checking to see the 
difference between the original value of an attribute and the current value 
-- in particular, some of the validation going on should prohibit a change 
that causes a particular check to fail, but only if that check wasn't 
already failing (e.g. some legacy)

I see that I can use inspect() to get the history of attributes, but that 
quickly gets unwieldy when working with a large number of attributes.  What 
I'd love to be able to do is something like:

def do_something(self):
    orig = get_original_version(self)
    delta = self.value - orig.value
    # ....

Is there a simple way to accomplish this?  Right now I'm doing something 
like:

orig_value, = inspect(self).attrs.value.history.non_added or 
(default_value, )

which seems messy and only works for scalar values.

-- Daniel

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