code: def write(self, *data):
          
          for l in data:
              ## print("XXX write: '%s'" % l)
              for i in str(l):
                  if i == '\n':
                      self.current_line_number += 1
                      pass
                  pass
              pass
          return super(LineMapWalker, self).write(*data)
docs: Augment write routine to keep track of current line