return encoded representation

def binary(self):
        """
        return encoded representation
        """
        if isinstance(self.value, list):
            length = len(self.value)
            if length == 0:
                return b_chr(_TAG_NIL_EXT)
            elif length > 4294967295:
                raise OutputException('uint32 overflow')
            elif self.improper:
                return (
                    b_chr(_TAG_LIST_EXT) +
                    struct.pack(b'>I', length - 1) +
                    b''.join([_term_to_binary(element)
                              for element in self.value])
                )
            else:
                return (
                    b_chr(_TAG_LIST_EXT) +
                    struct.pack(b'>I', length) +
                    b''.join([_term_to_binary(element)
                              for element in self.value]) +
                    b_chr(_TAG_NIL_EXT)
                )
        else:
            raise OutputException('unknown list type')