How to Control Binding Order in Tkinter Text Widgets?

Event Binding Order in Tkinter Text Widget

When binding events to a Tkinter Text widget, it's important to consider the order in which bindings are processed. By default, the widget's bindings are processed first, followed by the class bindings.

Problem: Binding Occurs Before Content Change

The problem described in the question arises when the self binding is called before the Text widget's binding. In this case, the widget's binding changes the text content, which triggers the self binding too early.

Solution: Changing Binding Order

There are several ways to adjust the binding order to resolve this issue.

1. Rearrange Bindtags:
   Each widget has a set of bindtags. You can modify the order of these tags to ensure that the class binding is processed before the widget binding.
2. Introduce Additional Bindtag:
   Create a new bindtag and assign it to your self binding. This bindtag should be placed after the class bindtag in the widget's tags.

Consequences of Binding Order Changes

Rearranging Bindtags:

• Affects all bindings on that widget.
• May break existing bindings that rely on the current order.

Introducing Additional Bindtag:

• Allows you to control which bindings happen before and after class bindings.
• Provides greater flexibility and avoids breaking existing bindings.

Example Code

The code below demonstrates the two approaches to adjusting the binding order:

<code class="python">import tkinter as tk

def on_keypress(event):
    txt = event.widget.get('1.0', 'end')
    status['text'] = f"The value in the text widget is {txt}."

root = tk.Tk()

# Widget with default bindtags
text1 = tk.Text(root, height=5, width=30)
text1.pack()

# Widget with reversed bindtags
text2 = tk.Text(root, height=5, width=30)
text2.bindtags(('Text', '.text2', '.', 'all'))
text2.pack()

# Widget with additional bindtag
text3 = tk.Text(root, height=5, width=30)
text3.bindtags(('.text3', 'Text', 'post-class-bindings', '.', 'all'))
text3.pack()

# Label showing the value in the text widgets
status = tk.Label(root, justify="left")
status.pack()

# Bind to <KeyPress> event
text1.bind('<KeyPress>', on_keypress)
text2.bind('<KeyPress>', on_keypress)
text3.bind_class('post-class-bindings', '<KeyPress>', on_keypress)

root.mainloop()</code>

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