code: def get_plotable3d(self):
          
          polyhedra = sum([polyhedron.get_plotable3d() 
                           for polyhedron in self.polyhedra], [])
          return polyhedra + self.surface.get_plotable3d()
docs: :returns: matplotlib Poly3DCollection
          :rtype: list of mpl_toolkits.mplot3d