code: def huffman_conv2str(cls, bit_str, bit_len):
          # type: (int, int) -> str
          
          assert(bit_str >= 0)
          assert(bit_len >= 0)
  
          byte_len = bit_len // 8
          rem_bit = bit_len % 8
          if rem_bit != 0:
              bit_str <<= 8 - rem_bit
              byte_len += 1
  
          # As usual the list/join tricks is a performance trick to build
          # efficiently a Python string
          s = []  # type: List[str]
          i = 0
          while i < byte_len:
              s.insert(0, chb((bit_str >> (i * 8)) & 0xFF))
              i += 1
          return b''.join(s)
docs: huffman_conv2str converts a bitstring of bit_len bitlength into a
          binary string. It DOES NOT compress/decompress the bitstring!
  
          @param int bit_str: the bitstring to convert.
          @param int bit_len: the bitlength of bit_str.
          @return str: the converted bitstring as a bytestring.
          @raise AssertionError