Check that tokens and embedding are in the format for __setitem__.

def _check_vector_update(self, tokens, new_embedding):
        """Check that tokens and embedding are in the format for __setitem__."""
        assert self._idx_to_vec is not None, '`idx_to_vec` has not been initialized.'

        if not isinstance(tokens, (list, tuple)) or len(tokens) == 1:
            assert isinstance(new_embedding, nd.NDArray) and len(new_embedding.shape) in [1, 2], \
                '`new_embedding` must be a 1-D or 2-D NDArray if `tokens` is a single token.'
            if not isinstance(tokens, (list, tuple)):
                tokens = [tokens]
            if len(new_embedding.shape) == 1:
                new_embedding = new_embedding.expand_dims(0)

        else:
            assert isinstance(new_embedding, nd.NDArray) and len(new_embedding.shape) == 2, \
                '`new_embedding` must be a 2-D NDArray if `tokens` is a list of multiple strings.'
        if self._idx_to_vec is not None:
            assert new_embedding.shape == (len(tokens), self._idx_to_vec.shape[1]), \
                'The length of `new_embedding` must be equal to the number ' \
                'of tokens and the width of new_embedding must be equal ' \
                'to the dimension of embedding of the glossary.'
        else:
            assert new_embedding.shape[0] == len(tokens), \
                'The length of `new_embedding` must be equal to the number of tokens'
        return tokens