- jedi#init_python is used to init the Python environment.
- jedi#setup_py_version is the single point where PythonJedi is
defined, and will configure `PythonJedi` to output an error in case
initialization failed.
- jedi#force_py_version_switch will throw an error when
g:jedi#force_py_version is not handled (e.g. invalid or "auto" and
unresolved).
- When g:jedi#force_py_version is provided, it will be used always.
- Use WarningMsg highlight for errors, which are centralized and
handled through exceptions.