Append conda tzdata location instead of overriding

[isuruf]

This matches the behaviour of the zoneinfo module in python 3.9

[mbargull]

conda-forge::python=3.9 builds only use conda-forge::tzdata:

$ python -c 'import sys, sysconfig; print(sys.version, sysconfig.get_config_var("TZPATH"), sep="\n")'
3.9.0 | packaged by conda-forge | (default, Oct 14 2020, 22:59:50) 
[GCC 7.5.0]
/opt/conda/envs/tmp/share/zoneinfo:/opt/conda/envs/tmp/share/tzinfo

[isuruf]

That isn't intended.

[mbargull]

The duplication is because we have https://github.com/conda-forge/python-feedstock/blob/master/recipe/build_base.sh#L239 as well as https://github.com/conda-forge/python-feedstock/blob/master/recipe/build_base.sh#L444.

[isuruf]

Yep, see conda-forge/python-feedstock#403

[mbargull]

From what you wrote, I assume you don't want https://github.com/conda-forge/python-feedstock/blob/master/recipe/build_base.sh#L239 but only https://github.com/conda-forge/python-feedstock/blob/master/recipe/build_base.sh#L444 ?
However, what is the advantage to have ours looked last? We probably have more up to date information than the system.

[ocefpaf]

We probably have more up to date information than the system.

Yep. My ubuntu only offers 2020a, we are shipping 2020d.

[dhirschfeld]

I think it would be surprising for a user to install the latest tzdata but have Python use an older system version in preference to what the user installed.

I was thinking of refactoring the logic to be:

def reset_tzpath(to=None):
    global TZPATH

    tzpaths = to
    if tzpaths is not None:
        if isinstance(tzpaths, (str, bytes)):
            raise TypeError(
                f"tzpaths must be a list or tuple, "
                + f"not {type(tzpaths)}: {tzpaths!r}"
            )

        if not all(map(os.path.isabs, tzpaths)):
            raise ValueError(_get_invalid_paths_message(tzpaths))
        base_tzpath = tzpaths
    else:
        env_var = os.environ.get("PYTHONTZPATH", None)
        if env_var is not None:
            base_tzpath = _parse_python_tzpath(env_var)
        else:
            base_tzpath = [os.path.join(sys.base_prefix, "share", "zoneinfo")]
            if sys.platform != "win32":
                extra_tzpath = [
                    "/usr/share/zoneinfo",
                    "/usr/lib/zoneinfo",
                    "/usr/share/lib/zoneinfo",
                    "/etc/zoneinfo",
                ]
                extra_tzpath = extra_tzpath.sort(
                    key=lambda x: not os.path.exists(x)
                )
                base_tzpath += extra_tzpath

    TZPATH = tuple(base_tzpath)

    if TZPATH_CALLBACKS:
        for callback in TZPATH_CALLBACKS:
            callback(TZPATH)

Thoughts?

[dhirschfeld]

...but as @ocefpaf mentioned, since tzdata is a dependency none of the others would then ever be chosen because the first entry would always be present.