code: def bits_to_bytes(bits):
      
      if len(bits) % 8 != 0:
          raise Exception("num bits must be multiple of 8")
  
      res = ""
  
      for x in six.moves.range(0, len(bits), 8):
          byte_bits = bits[x:x+8]
          byte_val = int(''.join(map(str, byte_bits)), 2)
          res += chr(byte_val)
  
      return utils.binary(res)
docs: Convert the bit list into bytes. (Assumes bits is a list
      whose length is a multiple of 8)