[Python-Dev] PEP 435: pickling enums created with the functional API (original) (raw)

Eli Bendersky eliben at gmail.com
Wed May 8 03:55:24 CEST 2013

On Tue, May 7, 2013 at 6:00 PM, Steven D'Aprano <steve at pearwood.info> wrote:

On 07/05/13 23:34, Eli Bendersky wrote:

One of the contended issues with PEP 435 on which Guido pronounced was the functional API, that allows created enumerations dynamically in a manner similar to namedtuple:

Color = Enum('Color', 'red blue green') The biggest complaint reported against this API is interaction with pickle. As promised, I want to discuss here how we're going to address this concern.

Does this issue really need to be solved before 435 is accepted? As the Zen says: Now is better than never. Although never is often better than right now. Solving the pickle issue is a hard problem, but not a critical issue. namedtuple has had the same issue since its inception, only worse because there is no class syntax for namedtuple. This has not been a barrier to the success of namedtuple. Agreed

Or rather, the issue is not with Enum, or namedtuple, but pickle. Any dynamically-created type will have this issue:

import pickle

def example(name):

... return type(name, (object,), {}) ... instance = example("Foo")() pickle.dumps(instance) Traceback (most recent call last): File "", line 1, in pickle.PicklingError: Can't pickle <class '_main_.Foo'>: attribute lookup main.Foo failed I don't think it is unreasonable to chalk it up to a limitation of pickle, and say that unless you can meet certain conditions, you won't be able to pickle your instance. Either way, approval of PEP 435 should not be dependent on fixing the pickle issue.

Just to be clear- it was not my intention to delay PEP 435 because of this issue. I don't see it as a blocker to pronouncement and from a private correspondence with Guido, he doesn't either.

I merely wanted to start a separate thread because I didn't want this discussion to overwhelm the pronouncement thread.

Eli -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.python.org/pipermail/python-dev/attachments/20130507/b4223e39/attachment.html>

More information about the Python-Dev mailing list