def add_vertices(self, vertices, vid_field=None):
        """
        Add vertices to the SGraph. Vertices should be input as a list of
        :class:`~turicreate.Vertex` objects, an :class:`~turicreate.SFrame`, or a
        pandas DataFrame. If vertices are specified by SFrame or DataFrame,
        ``vid_field`` specifies which column contains the vertex ID. Remaining
        columns are assumed to hold additional vertex attributes. If these
        attributes are not already present in the graph's vertex data, they are
        added, with existing vertices acquiring the value ``None``.

        Parameters
        ----------
        vertices : Vertex | list [Vertex] | pandas.DataFrame | SFrame
            Vertex data. If the vertices are in an SFrame or DataFrame, then
            ``vid_field`` specifies the column containing the vertex IDs.
            Additional columns are treated as vertex attributes.

        vid_field : string, optional
            Column in the DataFrame or SFrame to use as vertex ID. Required if
            vertices is an SFrame. If ``vertices`` is a DataFrame and
            ``vid_field`` is not specified, the row index is used as vertex ID.

        Returns
        -------
        out : SGraph
            A new SGraph with vertices added.

        See Also
        --------
        vertices, SFrame, add_edges

        Notes
        -----
        - If vertices are added with indices that already exist in the graph,
          they are overwritten completely. All attributes for these vertices
          will conform to the specification in this method.

        Examples
        --------
        >>> from turicreate import SGraph, Vertex, SFrame
        >>> g = SGraph()

        Add a single vertex.

        >>> g = g.add_vertices(Vertex(0, attr={'breed': 'labrador'}))

        Add a list of vertices.

        >>> verts = [Vertex(0, attr={'breed': 'labrador'}),
                     Vertex(1, attr={'breed': 'labrador'}),
                     Vertex(2, attr={'breed': 'vizsla'})]
        >>> g = g.add_vertices(verts)

        Add vertices from an SFrame.

        >>> sf_vert = SFrame({'id': [0, 1, 2], 'breed':['lab', 'lab', 'vizsla']})
        >>> g = g.add_vertices(sf_vert, vid_field='id')
        """

        sf = _vertex_data_to_sframe(vertices, vid_field)

        with cython_context():
            proxy = self.__proxy__.add_vertices(sf.__proxy__, _VID_COLUMN)
            return SGraph(_proxy=proxy)