<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:

def _normalize_basedir(basedir=None):
    '''
    Takes a basedir argument as a string or a list. If the string or list is
    empty, then look up the default from the 'reposdir' option in the yum
    config.

    Returns a list of directories.
    '''
    # if we are passed a string (for backward compatibility), convert to a list
    if isinstance(basedir, six.string_types):
        basedir = [x.strip() for x in basedir.split(',')]

    if basedir is None:
        basedir = []

    # nothing specified, so use the reposdir option as the default
    if not basedir:
        basedir = _get_yum_config_value('reposdir')

    if not isinstance(basedir, list) or not basedir:
        raise SaltInvocationError('Could not determine any repo directories')

    return basedir