[graph-tool] Vertex position in property map

Hi all, I'm trying to story vertex positions in a property map. Why doesn't it work the way I try? from graph_tool.all import * import numpy as np g = Graph() pos = g.new_vertex_property('object') for i in range(1, 3): v = g.add_vertex() pos[v] = np.array([i, i]) graph_draw(g, pos=pos) Thanks Haiko