docs: def setitem_without_overwrite(d, key, value):
      """
      @param d: An instance of dict, that is: isinstance(d, dict)
      @param key: a key
      @param value: a value to associate with the key
  
      @return: None
  
      @raise: OverwriteError if the key is already present in d.
      """
      if key in d:
          raise OverwriteError(key, value, d[key])
      else:
          dict.__setitem__(d, key, value)