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()

