code: def _autoscroll(sbar, first, last):
      
      first, last = float(first), float(last)
      if first <= 0 and last >= 1:
          sbar.grid_remove()
      else:
          sbar.grid()
      sbar.set(first, last)
docs: Hide and show scrollbar as needed.
      Code from Joe English (JE) at http://wiki.tcl.tk/950