[Python-Dev] Choosing an official stance towards module deprecation in Python 3

[Guido van Rossum]

#2 sounds fine to me.

On Tue, Sep 8, 2015 at 9:59 AM, Brett Cannon <bcannon at gmail.com> wrote:

> There are two discussions going on in the issue tracker about deprecating
> some modules and it has led to the inevitable discussion of Python 2/3
> compatibility (I'm not even going to bother mentioning the issue #s as this
> thread is not about the modules specifically but module deprecation in
> general). Because I'm tired of rehashing the same discussion every time a
> module deprecation comes up I would like to make an official decision that
> we can follow any time we decide to deprecate a module.
>
> The approaches to module deprecation I have seen are:
> 1. Nothing changes to the deprecation process; you deprecate a module and
> remove it in one to two releases
> 2. Deprecate the module but with no plans for removal until Python 2.7
> reaches its EOL (I have been calling this Python 4)
> 3. Document the deprecation but no actual code deprecation
>
> I'm personally in the #2 camp. I want users to be fully aware that the
> module in question is not being updated and possibly not even getting
> non-critical bugfixes, but it's still there in Python 3 in order to make
> sure that you can have code which straddles Python 2 & 3 more easily.
>
> I don't like #1 because when the module exists in python 2.7 as it makes
> transitioning from Python 2 a bit harder. Leaving code in the stdlib as
> deprecated isn't going to kill us, especially if we make it clear the code
> only exists for transitioning purposes and you very well may have to work
> around any bugs you come across (and yes, this means changing my stance for
> the formatter module's deprecation).
>
> I don't like #3 because if you have an API memorized or you copied some
> code you found online you very well may not realize a module is deprecated.
> It's not difficult to silence a deprecation warning and you can make it so
> that even if you use -Werror your deprecated module imports continue to
> work without throwing an exception while all other deprecations do throw an
> exception.
>
> Whatever decision we come to I will update PEP 4 and then personally go
> through the various deprecated modules in Python 3.6 and tweak them as
> necessary to follow whatever policy we come up with.
>
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-- 
--Guido van Rossum (python.org/~guido)
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