code: def calc_checksum(self, data):
          
  
          output = 0
          length = len(data)
          for value in data:
              output += int(value, 16)
  
          output += length
          checksum = hex(output & int('0x007F', 16)).lstrip("0x")
          data.append(checksum)
          data.append('F7')
          return data
docs: Calculate the checksum we need