There is a bug in PolygonInteractor -- the non-existent 'verts' is reference. Note, there is a verts attribute in some of the inherited Polygon classes, but not in the Polygon class itself. This is easy to fix. Just remove the unnecessary line: self.poly.verts = list(self.poly.verts) and change all references of poly.verts to poly.xy. This works fine for me. I found this while creating an interactive polygon creator, attached for those interested. Feel free to use this routine however you wish.