code: def update(self, old_line, new_line, once=False):
          
          nb = 0
          for block in self.blocks:
              nb += block.update(old_line, new_line, once=once)
              if nb and once:
                  return nb
          return nb
docs: Replace all lines matching `old_line` with `new_line`.
  
          If ``once`` is set to True, remove only the first instance.