code: def add_key(self, key, first=False):
          
          if first:
              self.keys = [key] + self.keys
          else:
              self.keys.append(key)
          if isinstance(key, VSpaceKey):
              self.space = key
docs: Adds the given key to this row.
  
          :param key: Key to be added to this row.
          :param first: BOolean flag that indicates if key is added at the beginning or at the end.