check-py-ver

#!/usr/bin/env bash
#
#   check-py-ver - confirm Python seems right for the tox environment
#
#   Bad/missing `base_python` settings can cause tox to quietly use tox's
#   Python version rather than one matching the py* factor in the
#   environment name. For example, if in `[testenv]` you specify
#   `base_python = py3.8: ...`, that leaves `base_python` unset for a tox
#   environment with factor `py3.9`. This will cause tox to create or even
#   change the py3.9 environment to use e.g. Python 3.11 (if that's what
#   tox itself is using) instead of 3.9 and carry on as if everything is ok.
#
#   Calling this script at the start of `commands = ...` allows us to
#   ensure that, even with possibly subtle configuration errors, we really
#   are using the Python version matching the py* factor in the environment
#   name.
#

pyver=py$(python -c '
import sys
vi = sys.version_info
print("{}.{}".format(vi.major, vi.minor))
')

[[ ${TOX_ENV_NAME%%-*} == $pyver ]] || {
    echo 1>&2 "check-py-ver:" \
        "Python version $pyver does not match environment ${TOX_ENV_NAME}"
    exit 5
}