code: def is_equal(self, other):
          
          if not isinstance(other, DictCell):
              return False
          for (this, that) in itertools.izip_longest(self, other):
              if this[0] != that[0]:
                  # compare key names
                  return False
              if not this[1].is_equal(that[1]):
                  # compare cells
                  return False
          return True
docs: Two DictCells are equal when they share ALL Keys,  and all of their 
          is_equal() methods return True.  This ensures substructure equality.