def _validate_indices(self, indices=None):
if indices is None:<EOL><INDENT>indices = self.default_indices<EOL><DEDENT>if isinstance(indices, six.string_types):<EOL><INDENT>indices = [indices]<EOL><DEDENT>return indices<EOL>
Return a valid list of indices.

        `indices` may be a string or a list of strings.
        If `indices` is not supplied, returns the default_indices.