code: def vertices(self):
          
  
          if self._faces is None:
              if self._vertices is None:
                  return None
              self.triangulate()
          return self._vertices
docs: Return an array (Nf, 3) of vertices.
  
          If only faces exist, the function computes the vertices and
          returns them.
          If no vertices or faces are specified, the function returns None.