class ClearWindow:
  menudefs = [
    ('options', [None,
           ('Clear Shell Window', '<<clear-window'),
           ]), ]
 
  def __init__(self, editwin):
    self.editwin = editwin
    self.text = self.editwin.text
    self.text.bind("<<clear-window", self.clear_window2)
 
    self.text.bind("<<undo", self.undo_event) # add="+" doesn't work
 
  def undo_event(self, event):
    text = self.text
 
    text.mark_set("iomark2", "iomark")
    text.mark_set("insert2", "insert")
    self.editwin.undo.undo_event(event)
 
    # fix iomark and insert
    text.mark_set("iomark", "iomark2")
    text.mark_set("insert", "insert2")
    text.mark_unset("iomark2")
    text.mark_unset("insert2")
 
  def clear_window2(self, event): # Alternative method
    # work around the ModifiedUndoDelegator
    text = self.text
    text.undo_block_start()
    text.mark_set("iomark2", "iomark")
    text.mark_set("iomark", 1.0)
    text.delete(1.0, "iomark2 linestart")
    text.mark_set("iomark", "iomark2")
    text.mark_unset("iomark2")
    text.undo_block_stop()
    if self.text.compare('insert', '<', 'iomark'):
      self.text.mark_set('insert', 'end-1c')
    self.editwin.set_line_and_column()
 
  def clear_window(self, event):
    # remove undo delegator
    undo = self.editwin.undo
    self.editwin.per.removefilter(undo)
 
    # clear the window, but preserve current command
    self.text.delete(1.0, "iomark linestart")
    if self.text.compare('insert', '<', 'iomark'):
      self.text.mark_set('insert', 'end-1c')
    self.editwin.set_line_and_column()
 
    # restore undo delegator
    self.editwin.per.insertfilter(undo)

[ClearWindow]
enable=1
enable_editor=0
enable_shell=1
[ClearWindow_cfgBindings]
clear-window=<Control-Key-w>