code: def to_bytes(s, encoding=None, errors='strict'):
      
      encoding = encoding or 'utf-8'
      if isinstance(s, bytes):
          if encoding != 'utf-8':
              return s.decode('utf-8', errors).encode(encoding, errors)
          else:
              return s
      if not is_string(s):
          s = string_type(s)
      return s.encode(encoding, errors)
docs: Returns a bytestring version of 's',
  encoded as specified in 'encoding'.