Re: Minimum supported version of Python?

On Sat, 2014-03-15 at 20:55 -0400, Tom Lane wrote:
> Our documentation claims that the minimum Python version for plpython
> is 2.3. However, an attempt to build with that on an old Mac yielded
> a bunch of failures in the plpython_types regression test,

It has frequently been the case that the last supported version does not
fully pass the regression test, because of the overhead of maintaining
variant files. The last supported version is the one that compiles and
works. You will note that 2.2 no longer compiles. (It also failed the
regression tests for a while before it started not compiling.)
Typically, versions fall out of support because we add new functionality
that the old Python versions cannot support anymore.

> all of the form
>
> ! ERROR: could not import a module for Decimal constructor
> ! DETAIL: ImportError: No module named decimal

You can make this work by manually installing the decimal module
(because it was not part of the core in Python 2.3). Otherwise, this
test result legitimately alerts you that some feature is not fully
working and that you need to adjust your installation.

> A quick trawl through the buildfarm revealed no evidence that we're
> actually testing anything older than Python 2.5, which is why this
> wasn't evident awhile ago.

It was known when the decimal feature was committed. I regularly test
all supported Python versions.

> It looks like the failing test cases date back to PG 9.0.

This feature is new in 9.4, so that can't be quite right.

We have added and dropped supported Python versions in most major
releases over time, so there will likely be different results and
different considerations in each major release.

Certainly, all Python versions listed as supported in each major PG
release actually worked at the time of release.

> Personally I have no desire to put any effort into fixing this, and
> thus suggest that we just change the documentation to specify that 2.5
> is the minimum Python version since 9.0. Does anybody else want to
> work harder on it, and if so what would you propose doing exactly?

It is debatable whether 2.3 should still be considered supported in 9.4.
If we do drop it, then the supported version should be 2.4. Personally,
I think everything is fine as it is.