code: def _checksum(self):
          
          for line in [self._line1, self._line2]:
              check = 0
              for char in line[:-1]:
                  if char.isdigit():
                      check += int(char)
                  if char == "-":
                      check += 1
  
              if (check % 10) != int(line[-1]):
                  raise ChecksumError(self._platform + " " + line)
docs: Performs the checksum for the current TLE.