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.