docs: def _deepcopy(self, x, memo=None):
          """Deepcopy helper for the data dictionary or list.
  
          Regular expressions cannot be deep copied but as they are immutable we
          don't have to copy them when cloning.
          """
          if not hasattr(x, 'items'):
              y, is_list, iterator = [], True, enumerate(x)
          else:
              y, is_list, iterator = {}, False, iteritems(x)
  
          if memo is None:
              memo = {}
          val_id = id(x)
          if val_id in memo:
              return memo.get(val_id)
          memo[val_id] = y
  
          for key, value in iterator:
              if isinstance(value, (dict, list)) and not isinstance(value, SON):
                  value = self._deepcopy(value, memo)
              elif not isinstance(value, RE_TYPE):
                  value = copy.deepcopy(value, memo)
  
              if is_list:
                  y.append(value)
              else:
                  if not isinstance(key, RE_TYPE):
                      key = copy.deepcopy(key, memo)
                  y[key] = value
          return y