def splitarg_or_varargs(*args):
    """Construct a list of strings either from a single space-separated
string or from a variable number of string arguments.

    >>> splitarg_or_varargs('x y z')
    ['x', 'y', 'z']
    >>> splitarg_or_varargs('x', 'y', 'z')
    ['x', 'y', 'z']

    """
    if len(args) == 1:
        return args[0].split()
    else:
        return list(args)