code: def _group_centroid(mol, ilabels, group_atoms):
          
          c1x, c1y, c1z = 0.0, 0.0, 0.0
          for i in group_atoms:
              orig_idx = ilabels[i-1]
              oa1 = mol.GetAtom(orig_idx)
              c1x += float(oa1.x())
              c1y += float(oa1.y())
              c1z += float(oa1.z())
          num_atoms = len(group_atoms)
          c1x /= num_atoms
          c1y /= num_atoms
          c1z /= num_atoms
          return c1x, c1y, c1z
docs: Calculate the centroids of a group atoms indexed by the labels of inchi
  
          Args:
              mol: The molecule. OpenBabel OBMol object
              ilabel: inchi label map
  
          Returns:
              Centroid. Tuple (x, y, z)