text: 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()
  