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

[Yury Selivanov]

Big +1 from me.  The whole point of DeprecationWarnings is to be
visible so that they are resolved faster.  The current behaviour
allows them to go unnoticed for the majority of Python users.

Yury

On Sun, Nov 5, 2017 at 9:05 PM, Nick Coghlan <ncoghlan at gmail.com> wrote:
> On the 12-weeks-to-3.7-feature-freeze thread, Jose Bueno & I both
> mistakenly though the async/await deprecation warnings were missing
> from 3.6.
>
> They weren't missing, we'd just both forgotten those warnings were off
> by default (7 years after the change to the default settings in 2.7 &
> 3.2).
>
> 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, and app devs having to silence it explicitly
> during application startup (before they start importing third party
> modules) if they don't want their users seeing it when running on the
> latest Python version (e.g. this would be suitable for open source
> apps that get integrated into Linux distros and use the system Python
> there).
>
> This will also restore the previously clear semantic and behavioural
> different between PendingDeprecationWarning (hidden by default) and
> DeprecationWarning (visible by default).
>
> 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`).
>
> (Structurally, I'd probably put that at the end of the warnings
> listing as a short introduction to warnings management, with links out
> to the relevant sections of the documentation, and just use
> DeprecationWarning as the specific example)
>
> Cheers,
> Nick.
>
> [1] https://docs.python.org/3/library/exceptions.html#DeprecationWarning
>
> --
> Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
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