I can't figure out how I am doing this wrong: ``` from graph_tool.all import * graph = collection.data['polbooks'] a = graph.vp['value'] print a a.get_2d_array([0]) ``` I get this trace: ``` <PropertyMap object with key type 'Vertex' and value type 'string', for Graph 0x7fd6f9440f90, at 0x7fd6f37322d0> --------------------------------------------------------------------------- IndexError Traceback (most recent call last) <ipython-input-122-19dc354c8941> in <module>() 2 a = graph.vp['value'] 3 print a ----> 4 a.get_2d_array([0]) /home/joelmo/.nix-profile/lib/python2.7/site-packages/graph_tool/__init__.pyc in get_2d_array(self, pos) 663 for v in iters: 664 for i in range(len(p)): --> 665 a[i][int(v)] = p[i][v] 666 if len(a) == 1: 667 a = a[0] IndexError: list assignment index out of range ```