code: def from_molecular_graph(cls, molecular_graph, labels=None):
          
          if labels is None:
              labels = molecular_graph.numbers.astype(int)
          return cls(molecular_graph.distances, labels)
docs: Initialize a similarity descriptor
  
             Arguments:
               molecular_graphs  --  A MolecularGraphs object
               labels  --  a list with integer labels used to identify atoms of
                           the same type. When not given, the atom numbers from
                           the molecular graph are used.