JezK
Edit File: WidgetRedirector.py
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()