How can you execute custom code after text updates in Tkinter\'s Text widget?

How Do Bindings Function in the Tkinter Text Widget?

In Tkinter, when you interact with a text widget, your keystrokes trigger bindings associated with the widget. These bindings determine how the text is updated as you type. However, there are instances when you may want to execute your own code after text updates have occurred through built-in class bindings.

Behind the Scenes: Bind Tags and Event Handling

Tkinter utilizes bind tags to handle events. Each widget has a bind tag with the same name as the widget, and other bind tags include the widget's class, the root window's path, and the general "all" tag. Widgets are assigned bind tags that process events in sequence, starting with the most specific (widget) and ending with the least specific (all).

Resolving the Binding Order Issue

To bind self-defined events after class bindings, you have two options: reordering bind tags or introducing a new bind tag.

Option 1: Rearranging Bind Tags

By adjusting the sequence of bind tags, you can prioritize event processing for your custom bindings over class bindings. For instance, if you have a bind tag representing the widget ("entry1" in the code below), move it below the class bind tag ("Entry") in the list of bind tags:

<code class="python">entry1.bindtags(('Entry', '.entry1', '.', 'all'))</code>

Option 2: Introducing a New Bind Tag

Alternatively, you can create an extra bind tag that follows the class bind tag. Your bindings will then be attached to this new tag:

<code class="python">entry3.bindtags(('.entry3','Entry','post-class-bindings', '.', 'all'))

# Custom bindings are attached to the 'post-class-bindings' tag
entry3.bind_class("post-class-bindings", "<keypress>", OnKeyPress)</keypress></code>

Code Example

The following code illustrates the use of these techniques:

<code class="python">import Tkinter

def OnKeyPress(event):
    value = event.widget.get()
    string="value of %s is '%s'" % (event.widget._name, value)
    status.configure(text=string)

root = Tkinter.Tk()

entry1 = Tkinter.Entry(root, name="entry1")
entry2 = Tkinter.Entry(root, name="entry2")
entry3 = Tkinter.Entry(root, name="entry3")

entry1.bindtags(('.entry1', 'Entry', '.', 'all'))
entry2.bindtags(('Entry', '.entry2', '.', 'all'))
entry3.bindtags(('.entry3','Entry','post-class-bindings', '.', 'all'))

# Custom bindings are attached to the default tags
entry1.bind("<keypress>", OnKeyPress)

# Custom bindings are attached to the reordered tags
entry2.bind("<keypress>", OnKeyPress)

# Custom bindings are attached to the new 'post-class-bindings' tag
entry3.bind_class("post-class-bindings", "<keypress>", OnKeyPress)

root.mainloop()</keypress></keypress></keypress></code>

By running this code and pressing keys in the three entry widgets, you'll notice that the bindings for the first entry widget seem to trail behind by one character due to the default binding order. However, the bindings for the second and third entry widgets update the text correctly as you type.

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