code: def nvalues(self):
          
          if self._nvalues is None:
              self._nvalues = 0
              for val in self.values:
                  if type(val) == type(int):
                      self._nvalues += val
                  else:
                      self._nvalues = -1
                      break
  
          return self._nvalues
docs: Returns the number of values recorded on this single line. If the
          number is variable, it returns -1.