code: def needle_positions_to_bytes(self, needle_positions):
          
          bit = self.needle_positions
          assert len(bit) == 2
          max_length = len(needle_positions)
          assert max_length == self.number_of_needles
          result = []
          for byte_index in range(0, max_length, 8):
              byte = 0
              for bit_index in range(8):
                  index = byte_index + bit_index
                  if index >= max_length:
                      break
                  needle_position = needle_positions[index]
                  if bit.index(needle_position) == 1:
                      byte |= 1 << bit_index
              result.append(byte)
              if byte_index >= max_length:
                  break
          result.extend(b"\x00" * (25 - len(result)))
          return bytes(result)
docs: Convert the needle positions to the wire format.
  
          This conversion is used for :ref:`cnfline`.
  
          :param needle_positions: an iterable over :attr:`needle_positions` of
            length :attr:`number_of_needles`
          :rtype: bytes