Undo and Redo in an Tkinter Entry widget?

Question

Is there a way to add undo and redo capabilities in Tkinter Entry widgets or must I use single line Text widgets for this type of functionality?

If the latter, are there any tips I should follow when configuring a Text widget to act as an Entry widget?

Some features that might need tweaking include trapping the Return KeyPress, converting tab keypresses into a request to change focus, and removing newlines from text being pasted from the clipboard.

Answer 1

Disclaimer: these are just thoughts that come into my mind on how to implement it.

class History(object):

    def __init__(self):
        self.l = ['']
        self.i = 0

    def next(self):
        if self.i == len(self.l):
            return None
        self.i += 1
        return self.l[self.i]

    def prev(self):
        if self.i == 0:
            return None
        self.i -= 1
        return self.l[self.i]

    def add(self, s):
        del self.l[self.i+1:]
        self.l.append(s)
        self.i += 1

    def current(self):
        return self.l[self.i]

Run a thread that every X seconds (0.5?) save the state of the entry:

history = History()
...
history.add(stringval.get())

You can also set up events that save the Entry's status too, such as the pressure of Return.

prev = history.prev()
if prev is not None:
    stringvar.set(prev)

or

next = history.next()
if next is not None:
    stringvar.set(next)

Beware to set locks as needed.