Convert the Json Tree to SGraph

def _SGraphFromJsonTree(json_str):
    """
    Convert the Json Tree to SGraph
    """
    g = json.loads(json_str)
    vertices = [_Vertex(x['id'],
                dict([(str(k), v) for k, v in _six.iteritems(x) if k != 'id']))
                                                      for x in g['vertices']]
    edges = [_Edge(x['src'], x['dst'],
             dict([(str(k), v) for k, v in _six.iteritems(x) if k != 'src' and k != 'dst']))
                                                      for x in g['edges']]
    sg = _SGraph().add_vertices(vertices)
    if len(edges) > 0:
        sg = sg.add_edges(edges)
    return sg