code: def get_distance(self, i, j, jimage=None):
          
          return self[i].distance(self[j], jimage)
docs: Get distance between site i and j assuming periodic boundary
          conditions. If the index jimage of two sites atom j is not specified it
          selects the jimage nearest to the i atom and returns the distance and
          jimage indices in terms of lattice vector translations if the index
          jimage of atom j is specified it returns the distance between the i
          atom and the specified jimage atom.
  
          Args:
              i (int): Index of first site
              j (int): Index of second site
              jimage: Number of lattice translations in each lattice direction.
                  Default is None for nearest image.
  
          Returns:
              distance