code: def faces_sparse(self):
          
          sparse = geometry.index_sparse(
              column_count=len(self.vertices),
              indices=self.faces)
          return sparse
docs: A sparse matrix representation of the faces.
  
          Returns
          ----------
          sparse : scipy.sparse.coo_matrix
            Has properties:
            dtype : bool
            shape : (len(self.vertices), len(self.faces))