Ethan Furman added the comment:
When I implemented pickle support I did not have a complete understanding of
the pickle protocols nor how to best use them. As a result, I picked
__getnewargs__ and only supported protocols 2 and 3 (4 didn't exist yet).
Serhiy came along and explained a bunch of it to me, so now I know that
__reduce_ex__ is the best choice [1] as it supports all the protocol levels,
and is always used. The patch removes __getnewargs__ and makes __reduce_ex__
The One Obvious Way, but if it does not go in to 3.4.0 then I won't be able to
remove it because of backwards compatibility.
[1] Due to what I consider a bug in pickle (still need to create an issue for
it, I think) if:
class BaseClass:
def __reduce_ex__(self, proto):
return some_tuple
class SubClass(BaseClass):
def __reduce__(self):
return a_different_tuple
huh = SubClass()
pickle.dumps(huh)
the dumps call will use BaseClass.__reduce_ex__ and not SubClass.__reduce__.
For this reason Enum uses __reduce_ex__.
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