Re-binding “select all” in Text widget

Question

I\'m working with the Text widget and I have an issue about old-school shortcuts that Tk uses.

Ie:

Select all: Ctrl + / vs Ctrl + a

Answer 1

Feel free to use the following code or at least check out how the select_all methods are implemented in the DiacriticalEntry and DiacriticalText classes. If you choose to use the classes as they are in place of whatever widget you are currently using, you will also gain that advantange that users will be able to easily type in certain characters that would otherwise be more difficult to enter.

## {{{ http://code.activestate.com/recipes/576950/ (r3)
from tkinter import *
from tkinter.scrolledtext import ScrolledText
from unicodedata import lookup
import os

class Diacritical:
    """Mix-in class that adds keyboard bindings for accented characters, plus
    other common functionality.

    An inheriting class must define a select_all method that will respond
    to Ctrl-A."""

    accents = (('acute', "'"), ('grave', '`'), ('circumflex', '^'),
               ('tilde', '='), ('diaeresis', '"'), ('cedilla', ','),
               ('stroke', '/'), ('ring above', ';'))

    def __init__(self):
        # Fix some key bindings
        self.bind("<Control-Key-a>", self.select_all)
        # We will need Ctrl-/ for the "stroke", but it cannot be unbound, so
        # let's prevent it from being passed to the standard handler
        self.bind("<Control-Key-/>", lambda event: "break")
        # Diacritical bindings
        for a, k in self.accents:
            # Little-known feature of Tk, it allows to bind an event to
            # multiple keystrokes
            self.bind("<Control-Key-%s><Key>" % k,
                      lambda event, a=a: self.insert_accented(event.char, a))

    def insert_accented(self, c, accent):
        if c.isalpha():
            if c.isupper():
                cap = 'capital'
            else:
                cap = 'small'
            try:
                c = lookup("latin %s letter %c with %s" % (cap, c, accent))
                self.insert(INSERT, c)
                # Prevent plain letter from being inserted too, tell Tk to
                # stop handling this event
                return "break"
            except KeyError as e:
                pass

class DiacriticalEntry(Entry, Diacritical):
    """Tkinter Entry widget with some extra key bindings for
    entering typical Unicode characters - with umlauts, accents, etc."""

    def __init__(self, master=None, **kwargs):
        Entry.__init__(self, master, **kwargs)
        Diacritical.__init__(self)

    def select_all(self, event=None):
        self.selection_range(0, END)
        return "break"

class DiacriticalText(ScrolledText, Diacritical):
    """Tkinter ScrolledText widget with some extra key bindings for
    entering typical Unicode characters - with umlauts, accents, etc."""

    def __init__(self, master=None, **kwargs):
        ScrolledText.__init__(self, master, **kwargs)
        Diacritical.__init__(self)

    def select_all(self, event=None):
        self.tag_add(SEL, "1.0", "end-1c")
        self.mark_set(INSERT, "1.0")
        self.see(INSERT)
        return "break"


def test():
    frame = Frame()
    frame.pack(fill=BOTH, expand=YES)
    if os.name == "nt":
        # Set default font for all widgets; use Windows typical default
        frame.option_add("*font", "Tahoma 8")
    # The editors
    entry = DiacriticalEntry(frame)
    entry.pack(fill=BOTH, expand=YES)
    text = DiacriticalText(frame, width=76, height=25, wrap=WORD)
    if os.name == "nt":
        # But this looks better than the default set above
        text.config(font="Arial 10")
    text.pack(fill=BOTH, expand=YES)
    text.focus()
    frame.master.title("Diacritical Editor")
    frame.mainloop()

if __name__ == "__main__":
    test()
## end of http://code.activestate.com/recipes/576950/ }}}

Answer 2

The default bindings are applied to the widget class. When you do a bind, it affects a specific widget and that binding happens before the class binding. So what is happening is that your binding is happening and then the class binding is happening, which makes it seem as if your binding isn't working.

There are two ways to solve this. One, your ctext_selectall can return the string "break" which will prevent the class binding from firing. That should be good enough to solve your immediate problem.

The second solution involves changing the class binding so that your preferred binding applies to all text widgets. You would do this using the bind_class method.

Here's an example of rebinding the class:

def __init__(...):
    self.root.bind_class("Text","<Control-a>", self.selectall)

def selectall(self, event):
    event.widget.tag_add("sel","1.0","end")

effbot.org has a pretty decent writeup titled Events and Bindings. It goes into a little more detail about class and widget bindings and the order in which they occur.

Tk's binding mechanism is about the best of any GUI toolkit there is. Once you understand how it works (and it's remarkably simple) you'll find it's easy to augment or replace any or all of the default bindings.