VOTable serialization is not setting version configuration reliably

Description

Trying to write a VOTable using BINARY2 format breaks with:

Traceback (most recent call last):
  File "/Users/timj/work/lsstsw/build/dax_obscore/x.py", line 8, in <module>
    votable.set_all_tables_format("binary2")
  File "/Users/timj/work/lsstsw/miniconda/envs/lsst-scipipe-10.0.0/lib/python3.12/site-packages/astropy/io/votable/tree.py", line 4648, in set_all_tables_format
    table.format = format
    ^^^^^^^^^^^^
  File "/Users/timj/work/lsstsw/miniconda/envs/lsst-scipipe-10.0.0/lib/python3.12/site-packages/astropy/io/votable/tree.py", line 2602, in format
    if not self._config["version_1_3_or_later"]:
           ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^
KeyError: 'version_1_3_or_later'

This is because the _config property is not reliably set in some contexts. The code doesn't always crash because in some parts of the code the check is if not self._config.get("version_x_or_later") which returns False every time and assumes no new features are usable.

In one place in tree.py the code is doing the correct thing:

        if config is None:
            if hasattr(votable, "_get_version_checks"):
                config = votable._get_version_checks()
            else:
                config = {}
        self._config = config

but in every other place in tree.py it's doing:

        if config is None:
            config = {}
        self._config = config

and that seems to guarantee the crash.

I can do a PR to use that logic in all the places needed (and not sure if you also want the .get versus a direct access unified).

Expected behavior

BINARY2 output.

How to Reproduce

import astropy.io.votable.tree

votable = astropy.io.votable.tree.VOTableFile()
resource = astropy.io.votable.tree.Resource()
votable.resources.append(resource)
table0 = astropy.io.votable.tree.TableElement(votable)
resource.tables.append(table0)
votable.set_all_tables_format("binary2")

Versions

import astropy
astropy.system_info()

platform
--------
platform.platform() = 'macOS-15.5-arm64-arm-64bit'
platform.version() = 'Darwin Kernel Version 24.5.0: Tue Apr 22 19:54:49 PDT 2025; root:xnu-11417.121.6~2/RELEASE_ARM64_T6000'
platform.python_version() = '3.12.10'

packages
--------
astropy              7.1.0
numpy                2.0.2
scipy                1.13.1
matplotlib           3.10.1
pandas               2.2.3
pyerfa               2.0.1.5

I should add that adding the _get_version_checks call into the TableElement constructor fixes the problem and the BINARY2 output is written correctly.

Also I have just learned:

>>> from astropy.io.votable.tree import TimeSys
>>> TimeSys(ID="sys", timeorigin="MJD-origin", timescale="UTC")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/timj/work/lsstsw/miniconda/envs/lsst-scipipe-10.0.0/lib/python3.12/site-packages/astropy/io/votable/tree.py", line 2057, in __init__
    if not config["version_1_4_or_later"]:
           ~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^
KeyError: 'version_1_4_or_later'

which can be fixed by passing in a config parameter but where does one obtain that config using public APIs? All I can work out is:

>>> votable = VOTableFile(version="1.5")
>>> votable._get_version_checks()
{'version_1_1_or_later': True, 'version_1_2_or_later': True, 'version_1_3_or_later': True, 'version_1_4_or_later': True, 'version_1_5_or_later': True}

but that is the private API and even if I were to use votable._config to get it it's not filled in.

@tomdonaldson

cc @tomdonaldson @Deen-dot ?

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VOTable serialization is not setting version configuration reliably #18356

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VOTable serialization is not setting version configuration reliably #18356

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timj commented on Jun 26, 2025

timj commented on Jun 27, 2025

pllim commented on Jun 27, 2025

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