code: def distance(self, i, j):
          # TODO: check docstring
          
  
          a, b = i, j
  
          if a.name() > b.name():
              a, b = b, a
          
          return self._matrix[self._nodes[a.name()]][self._nodes[b.name()]]
docs: Returns the distance between node i and node j
          
          Parameters
          ----------
          i : type
              Descr
          j : type
              Desc
              
          Returns
          -------
          float
              Distance between node i and node j.