code: def from_molecule(cls, molecule, labels=None):
          
          if labels is None:
              labels = molecule.numbers
          return cls(molecule.distance_matrix, labels)
docs: Initialize a similarity descriptor
  
             Arguments:
               molecule  --  a Molecules object
               labels  --  a list with integer labels used to identify atoms of
                           the same type. When not given, the atom numbers from
                           the molecule are used.