undo and redo ?

Diez B. Roggisch deets_noospaam at web.de
Fri Jan 2 14:53:42 CET 2004

> I'm coding with Tkinter and i wonder whether we could get current OS'
> clipboard available, and event more, anyone can inspires me how we can
> achieve undo and redo function ?

When working with a MVC-approach, the actions you the user can invoke on the
model could be created as objects that know how to undo/invert their
effects. Then you store a list of these actions and performing undo takes
the last action and apply its inverted action to your model. Right from my

class InsertAction:
  def __init__(_, index, needle):
    _.index = index
    _.needle = needle

  def do(_, haystack):
    haystack[index:index] = _.needle
  def undo(_, haystack):
    del haystack[_.index : _.index + len(_.needle)]

Hope this gives you an idea. You can also have to types of actions -
primitive and complex. Performing undo will then undo all primitve actions
until the action queue is empty or a complex actions is reached. This
allows e.g. in a text-editor to perform undo subsequently inserted
characters at once.



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