Python tkinter text modified callback

Question

In python 2.7, I am trying to get a callback every time something is changed in the Tkinter Text widget.

The program uses multiple frames based on code found here:

Answer 1

I integrated the above <<TextModified>> example in my code and it worked quite well, except that it was interfering with some edit_modified() commands.

Fortunately, the tkinter Text window has a poorly documented feature which is as good and is fully compatible with the edit_modified() get or set commands: the predefined <<Modified>> tag. You don't even have to create it, it works out-of-the-box.

Here are the relevant parts of my code:

The "self" prefixes were removed, some adjustments may be needed

Put that in your Text gadget code:

title = set_title(fname, numbr)

text.bind("<<Modified>>", lambda dummy: save_indicator(title))

Make sure these functions are visible:

def set_title(fname, numbr):  
    "Creates a window title showing the save indicator,"  
    "the file name and a window number"  
    fname = strip_path(fname)  
    if not fname:  
        fname = "(New Document)"  
    return "+ {} - Window no.{}".format(fname, numbr)  

def strip_path(fname):  
    return os.path.split(fname)[-1]

def save_indicator(title, event=None):  
    "Update the window title"  
    titre = toggle_star(title)  
    text.winfo_toplevel().title(title)  

def toggle_star(title):  
    "Change the first character of the title"  
    chr='+'; chr0='x'  
    if text.edit_modified():  
        title = chr0 + title[1:]  
    else:  
        title = chr + title[1:]  
    return title  

Here is a complete working example with the predefined <<Modified>> tag:

def toggle_star(title):  
    "Change the color of the star in the title bar"  
    chr='+'; chr0='x'  
    if text.edit_modified():  
            title = chr0 + title[1:]  
    else:  
            title = chr + title[1:]  
    return title  

def set_title(fname, winno):  
    "Put save indicator, file name and window number in the title"  
    if not fname:  
            fname = "(New Document)"  
    return "+ {} - Window no.{}".format(fname, winno)  

def mockSave(title, event=None):  
    title = toggle_star(title)  
    root.winfo_toplevel().title(title)  
    text.edit_modified(0)  

def read_ed_mod():  
    print("text.edit_modified()=", text.edit_modified())  

def onModification(title, event=None):  
    title = toggle_star(title)  
    root.winfo_toplevel().title(title)  

from tkinter import *  

fname = 'blabla.txt'  
winno = 1 ;  

root = Tk()  
label = Label(root, anchor="w")  
text = Text(root, width=40, height=4)  
label.pack(side="bottom", fill="x")  
text.pack(side="top", fill="both", expand=True)  
Button(root, text='Mock Save', command= lambda: mockSave(title)).pack(side=LEFT)  
Button(root, text='Read ed_mod', command= lambda: read_ed_mod()).pack(side=RIGHT)  
text.bind('<<Modified>>', lambda event: onModification(title))  

title = set_title(fname, winno)  
root.winfo_toplevel().title(title)  
text.edit_modified(0)  

root.mainloop()  

Answer 2

I suggest a simpler approach. You can set up a proxy for the widget, and within that proxy you can detect whenever anything was inserted or deleted. You can use that information to generate a virtual event, which can be bound to like any other event.

Let's start by creating a custom text widget class, which you will use like any other text widget:

import Tkinter as tk

class CustomText(tk.Text):
    def __init__(self, *args, **kwargs):
        """A text widget that report on internal widget commands"""
        tk.Text.__init__(self, *args, **kwargs)

        # create a proxy for the underlying widget
        self._orig = self._w + "_orig"
        self.tk.call("rename", self._w, self._orig)
        self.tk.createcommand(self._w, self._proxy)

    def _proxy(self, command, *args):
        cmd = (self._orig, command) + args
        result = self.tk.call(cmd)

        if command in ("insert", "delete", "replace"):
            self.event_generate("<<TextModified>>")

        return result

The proxy in this example does three things:

1. First it calls the actual widget command, passing in all of the arguments it received.
2. Next it generates an event for every insert and every delete
3. Then it then generates a virtual event
4. And finally it returns the results of the actual widget command

You can use this widget exactly like any other Text widget, with the added benefit that you can bind to <<TextModified>>.

For example, if you wanted to display the number of characters in the text widget you could do something like this:

root = tk.Tk()
label = tk.Label(root, anchor="w")
text = CustomText(root, width=40, height=4)

label.pack(side="bottom", fill="x")
text.pack(side="top", fill="both", expand=True)

def onModification(event):
    chars = len(event.widget.get("1.0", "end-1c"))
    label.configure(text="%s chars" % chars)

text.bind("<<TextModified>>", onModification)

root.mainloop()