Python 3.x version support / dropping 3.5 and 3.6

[Raphaël Gomès]

On 2/27/22 22:19, Gregory Szorc wrote:
> 6.1 will be the last release to support Python 2.7. That means 6.2 
> will be Python 3 only.
>
> Currently our Python 3 support is for 3.5-3.10.
>
> Python 3.5 dropped out of support in September 2020 and Python 3.6 in 
> December 2021 (https://endoflife.date/python).
>
> Do we have any interest in dropping support for 3.5 or 3.6 in the 6.2 
> release?
>
> Features of interest in 3.6:
>
> * Variable type annotations. (Annotating on <3.6 requires special 
> syntax in comments)
> * Stabilization of async (unsure how much we'll adopt async though)
> * PEP 519 path protocol. This might enable us to clean up path 
> handling throughout the codebase by adopting richly typed path objects 
> with nice path-like primitives.
> * Enhancements to typing module to make it more useful.
>
> Features of interest in 3.7:
>
> * Postponed evaluation of type annotations (this is likely huge for 
> managing startup time)
> * importlib.resources (allows us to clean up non-module file loading)
> * @dataclass and data classes
>
> I think the only in-support major distro still supporting 3.5 is 
> Debian 9 Stretch, which goes out of support on 2022-06-30.
>
> 3.6 is more complicated. CentOS/RHEL 7 and Ubuntu 18.04 ship Python 
> 3.6. Although the former is already out of support. Ubuntu 18.04 is 
> still in main support until 2023-04-03 and has security support for 
> another few years.
>
> My pulse on the larger Python ecosystem is that 3.5 is mostly dead and 
> 3.6 is starting to wilt but not quite dead. Tons of projects dropped 
> 3.5 in the past year.
>
> **So I'd like to propose dropping support for Python 3.5 in 6.2.** 
> That would mean 6.1 is our last release with both Python 2.7 and 3.5 
> support.
>
Agreed, I think this is cautious enough.
> I don't think I can in good faith recommend dropping 3.6 support at 
> this time since it is still in wide use. But I do like the allure of 
> the above highlighted features in 3.7 and think they could lead to a 
> higher quality Mercurial and cleaner code base. If anyone else wants 
> to make the case for dropping 3.6 despite its apparent use in 
> supported distros, I'd love to hear it.
>
+1
>
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