code: def vertex_defects(mesh):
      
      angle_sum = np.asarray(mesh.face_angles_sparse.sum(axis=1)).flatten()
      defect = (2 * np.pi) - angle_sum
      return defect
docs: Return the vertex defects, or (2*pi) minus the sum of the angles
      of every face that includes that vertex.
  
      If a vertex is only included by coplanar triangles, this
      will be zero. For convex regions this is positive, and
      concave negative.
  
      Returns
      --------
      vertex_defect : (len(self.vertices), ) float
                       Vertex defect at the every vertex