[Python-Dev] Removing PendingDeprecationWarning

[Steve Dower]

On 27Mar2019 0324, Inada Naoki wrote:
> On Mon, Mar 25, 2019 at 10:11 PM Inada Naoki <songofacandy at gmail.com> wrote:
>>
>> C, Rust, Java, Ruby, PHP, don't have PendingDeprecation.
>> Programmers only need Deprecation.  Why programmers need PendingDeprecation
>> only in Python?
>>
> 
> Any comments about this?
> 
> I want to document PendingDeprecationWarning is deprecated [1].
> May I merge the PR?  Should I start poll on discuss.python.org?
> 
> [1]: https://github.com/python/cpython/pull/12505/files

There are two questions here:

1. Are we going to stop using it in CPython and the standard library?
2. Do we want everyone else to stop using it for their own purposes?

I think the first one is easy for us to answer (and personally, I don't 
care which way we go with it). However, deciding to stop using it 
ourselves is not the same as deprecating the class. So in this case, we 
would document that it is no longer used in CPython but is still 
available for other projects.

The second question is harder to answer, and in the absence of input 
from those who are already using it (or the absence of evidence that 
nobody else is using it), the best we can do is evaluate how much of a 
maintenance burden the class is.

In my opinion, it is a very low maintenance burden, and a very low 
cognitive burden on users, and so the cost of deprecating it on 
third-parties who are using it vastly outweighs the cost of leaving it 
alone.

If someone can show that either no third-parties are using it, or all 
those that do will probably never explicitly support Python 3.8 or 
later, or all those that do would prefer to stop using it, then I'll 
happily change my mind here. But right now, it seems like deprecating it 
will cause an unknown amount of churn for minimal benefit.

At most, I'd document it as "this will probably not survive to the next 
major change release, even though we aren't planning to do one yet" 
(much like the Py_UNICODE APIs). Ironically, PendingDeprecationWarning 
seems a pretty accurate way of indicating this state.

Cheers,
Steve