build on Python 2.6 broken and strongly suggested minimum version

[Fred Wright]

On Thu, 8 Dec 2022, James Browning via devel wrote:

> Selsky broke the build[1] back in May 2020 when switching the
> python_scripts variable in /wscript to a set when Python 2.6
> does not support sets. Given the lack of complaints, I suspect
> no one uses 2.6 anymore, which can be dropped.

Python 2.6 supports sets just fine; it just doesn't support the 
brace-style initializer.  The traditional set initializer works just fine.

I just submitted MR !1293 to fix it.

> I also think that we should drop all Python versions before
> 3.7 from first-tier support and only continue supporting them
> if it is not inconvenient or there is sufficient proven
> demand.

IMO, one should never drop support for something unless there's a good 
technical reason for it, not just being "too old".  Saving five characters 
isn't a "good technical reason".

The bar is set at 2.6 because supporting both Python 2 and Python 3 gets 
significantly more difficult without the 2.6 features.

It's even more important to support the widest possible range of Python 
versions as a *target*, since it exports Python modules for use by users, 
and any constraints on the version become constraints on the users' own 
Python code.

Fred Wright