def METHOD_NAME(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)
        elif sys.platform != "win32":
            base_tzpath = [
                "/usr/share/zoneinfo",
                "/usr/lib/zoneinfo",
                "/usr/share/lib/zoneinfo",
                "/etc/zoneinfo",
            ]
            base_tzpath.sort(key=lambda x: not os.path.exists(x))
        else:
            base_tzpath = ()
    TZPATH = tuple(base_tzpath)
    if TZPATH_CALLBACKS:
        for callback in TZPATH_CALLBACKS:
            callback(TZPATH)