from tkinter import *

class WidgetRedirector:

"""Support for redirecting arbitrary widget subcommands.

Some Tk operations don't normally pass through Tkinter. For example, if a
character is inserted into a Text widget by pressing a key, a default Tk
binding to the widget's 'insert' operation is activated, and the Tk library
processes the insert without calling back into Tkinter.

Although a binding to <Key> could be made via Tkinter, what we really want
to do is to hook the Tk 'insert' operation itself.

When a widget is instantiated, a Tcl command is created whose name is the
same as the pathname widget._w. This command is used to invoke the various
widget operations, e.g. insert (for a Text widget). We are going to hook
this command and provide a facility ('register') to intercept the widget
operation.

In IDLE, the function being registered provides access to the top of a
Percolator chain. At the bottom of the chain is a call to the original
Tk widget operation.

"""
def __init__(self, widget):
self._operations = {}
self.widget = widget # widget instance
self.tk = tk = widget.tk # widget's root
w = widget._w # widget's (full) Tk pathname
self.orig = w + "_orig"
# Rename the Tcl command within Tcl:
tk.call("rename", w, self.orig)
# Create a new Tcl command whose name is the widget's pathname, and
# whose action is to dispatch on the operation passed to the widget:
tk.createcommand(w, self.dispatch)

def __repr__(self):
return "WidgetRedirector(%s<%s>)" % (self.widget.__class__.__name__,
self.widget._w)

def close(self):
for operation in list(self._operations):
self.unregister(operation)
widget = self.widget; del self.widget
orig = self.orig; del self.orig
tk = widget.tk
w = widget._w
tk.deletecommand(w)
# restore the original widget Tcl command:
tk.call("rename", orig, w)

def register(self, operation, function):
self._operations[operation] = function
setattr(self.widget, operation, function)
return OriginalCommand(self, operation)

def unregister(self, operation):
if operation in self._operations:
function = self._operations[operation]
del self._operations[operation]
if hasattr(self.widget, operation):
delattr(self.widget, operation)
return function
else:
return None

def dispatch(self, operation, *args):
'''Callback from Tcl which runs when the widget is referenced.

If an operation has been registered in self._operations, apply the
associated function to the args passed into Tcl. Otherwise, pass the
operation through to Tk via the original Tcl function.

Note that if a registered function is called, the operation is not
passed through to Tk. Apply the function returned by self.register()
to *args to accomplish that. For an example, see ColorDelegator.py.

'''
m = self._operations.get(operation)
try:
if m:
return m(*args)
else:
return self.tk.call((self.orig, operation) + args)
except TclError:
return ""


class OriginalCommand:

def __init__(self, redir, operation):
self.redir = redir
self.operation = operation
self.tk = redir.tk
self.orig = redir.orig
self.tk_call = self.tk.call
self.orig_and_operation = (self.orig, self.operation)

def __repr__(self):
return "OriginalCommand(%r, %r)" % (self.redir, self.operation)

def __call__(self, *args):
return self.tk_call(self.orig_and_operation + args)


def main():
root = Tk()
root.wm_protocol("WM_DELETE_WINDOW", root.quit)
text = Text()
text.pack()
text.focus_set()
redir = WidgetRedirector(text)
global previous_tcl_fcn
def my_insert(*args):
print("insert", args)
previous_tcl_fcn(*args)
previous_tcl_fcn = redir.register("insert", my_insert)
root.mainloop()
redir.unregister("insert") # runs after first 'close window'
redir.close()
root.mainloop()
root.destroy()

if __name__ == "__main__":
main()