docs: def unicode2bytes(x, encoding='utf-8', errors='strict'):
      """
      Convert a unicode string to C{bytes}.
  
      @param x: a unicode string, of type C{unicode} on Python 2,
                or C{str} on Python 3.
      @param encoding: an optional codec, default: 'utf-8'
      @param errors: error handling scheme, default 'strict'
      @return: a string of type C{bytes}
      """
      if isinstance(x, text_type):
          x = x.encode(encoding, errors)
      return x