'Helper to validate passed path directory and append any subsequent
filename arguments.
Arguments:
path (str): Initial filesystem path.  Should expand to a valid
directory.
*args (list, optional): Any filename or path suffices to append to path
for returning.
Returns:
(list, str): path prepended list of files from args, or path alone if
no args specified.
Raises:
ValueError: if path is not a valid directory on this filesystem.'

@staticmethod
def _valid_path_append(path, *args):

    full_path = os.path.expanduser(path)
    res = []
    if (not os.path.exists(full_path)):
        os.makedirs(full_path)
    if (not os.path.isdir(full_path)):
        raise ValueError('path:    {0}    is    not    a    valid    directory'.format(path))
    for suffix_path in args:
        res.append(os.path.join(full_path, suffix_path))
    if (len(res) == 0):
        return path
    elif (len(res) == 1):
        return res[0]
    else:
        return res
