code: def _sync_code(self):
          
          new_code = []
          for line in self.lines:
              if isinstance(line, CodeAnswer):
                  new_code.append(line.dump())
              else:
                  new_code.append(line)
          self.code = '\n'.join(new_code)
docs: Syncs the current state of self.lines with self.code, the
          serializable string representing the set of code.