[Python-Dev] Proposal: go back to enabling DeprecationWarning by default

[Nick Coghlan]

On 6 November 2017 at 14:14, Barry Warsaw <barry at python.org> wrote:
> On Nov 5, 2017, at 18:05, Nick Coghlan <ncoghlan at gmail.com> wrote:
>
>> So my proposal is simple (and not really new): let's revert back to
>> the way things were in 2.6 and earlier, with DeprecationWarning being
>> visible by default
>
> +1
>
>> As part of this though, I'd suggest amending the documentation for
>> DeprecationWarning [1] to specifically cover how to turn it off
>> programmatically (`warnings.simplefilter("ignore",
>> DeprecationWarning)`), at the command line (`python -W
>> ignore::DeprecationWarning ...`), and via the environment
>> (`PYTHONWARNINGS=ignore::DeprecationWarning`).
>
> +1
>
> I’d also consider adding convenient shortcuts for each of these.  I think DeprecationWarning is special enough to warrant it.  Possibly:
>
> warnings.silence_deprecations()
> python -X silence-deprecations
> PYTHONSILENCEDEPRECATIONS=x

It could be interesting to combine this with Tim's suggestion of
putting an upper version limit on the silencing, so the above may look
like:

    warnings.ignore_deprecations((3, 7))
    python -X ignore-deprecations=3.7
    PYTHONIGNOREDEPRECATIONS=3.7

(Using "ignore" to match the existing action name so the intent is a
bit more self-explanatory)

The ignore_deprecations function would then look like:

    def ignore_deprecations(max_version):
        """Ignore DeprecationWarning on Python versions up to &
including the given one

        *max_version* is an iterable suitable for ordered comparison
against sys.version_info
        """
        if sys.version_info <= max_version:
            warnings.simplefilter('ignore', DeprecationWarning)

So the conventional usage would be that if you were regularly updating
your application, by the time Python 3.8 actually existed, the check
would have been bumped to say 3.8. But if you stopped updating (or the
publisher stopped releasing updates), you'd eventually start getting
deprecation warnings again as the underlying Python version changed.

I could definitely see that working well for the community Linux
distro use case, where there isn't necessarily anyone closely
monitoring old packages to ensure they're actively tracking upstream
releases (and attempting to institute more ruthless pruning processes
can lead to potentially undesirable community dynamics)

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia