1from Tkinter import *
2
3class WidgetRedirector:
4
5    """Support for redirecting arbitrary widget subcommands.
6
7    Some Tk operations don't normally pass through Tkinter.  For example, if a
8    character is inserted into a Text widget by pressing a key, a default Tk
9    binding to the widget's 'insert' operation is activated, and the Tk library
10    processes the insert without calling back into Tkinter.
11
12    Although a binding to <Key> could be made via Tkinter, what we really want
13    to do is to hook the Tk 'insert' operation itself.
14
15    When a widget is instantiated, a Tcl command is created whose name is the
16    same as the pathname widget._w.  This command is used to invoke the various
17    widget operations, e.g. insert (for a Text widget). We are going to hook
18    this command and provide a facility ('register') to intercept the widget
19    operation.
20
21    In IDLE, the function being registered provides access to the top of a
22    Percolator chain.  At the bottom of the chain is a call to the original
23    Tk widget operation.
24
25    """
26    def __init__(self, widget):
27        self._operations = {}
28        self.widget = widget            # widget instance
29        self.tk = tk = widget.tk        # widget's root
30        w = widget._w                   # widget's (full) Tk pathname
31        self.orig = w + "_orig"
32        # Rename the Tcl command within Tcl:
33        tk.call("rename", w, self.orig)
34        # Create a new Tcl command whose name is the widget's pathname, and
35        # whose action is to dispatch on the operation passed to the widget:
36        tk.createcommand(w, self.dispatch)
37
38    def __repr__(self):
39        return "WidgetRedirector(%s<%s>)" % (self.widget.__class__.__name__,
40                                             self.widget._w)
41
42    def close(self):
43        for operation in list(self._operations):
44            self.unregister(operation)
45        widget = self.widget; del self.widget
46        orig = self.orig; del self.orig
47        tk = widget.tk
48        w = widget._w
49        tk.deletecommand(w)
50        # restore the original widget Tcl command:
51        tk.call("rename", orig, w)
52
53    def register(self, operation, function):
54        self._operations[operation] = function
55        setattr(self.widget, operation, function)
56        return OriginalCommand(self, operation)
57
58    def unregister(self, operation):
59        if operation in self._operations:
60            function = self._operations[operation]
61            del self._operations[operation]
62            if hasattr(self.widget, operation):
63                delattr(self.widget, operation)
64            return function
65        else:
66            return None
67
68    def dispatch(self, operation, *args):
69        '''Callback from Tcl which runs when the widget is referenced.
70
71        If an operation has been registered in self._operations, apply the
72        associated function to the args passed into Tcl. Otherwise, pass the
73        operation through to Tk via the original Tcl function.
74
75        Note that if a registered function is called, the operation is not
76        passed through to Tk.  Apply the function returned by self.register()
77        to *args to accomplish that.  For an example, see ColorDelegator.py.
78
79        '''
80        m = self._operations.get(operation)
81        try:
82            if m:
83                return m(*args)
84            else:
85                return self.tk.call((self.orig, operation) + args)
86        except TclError:
87            return ""
88
89
90class OriginalCommand:
91
92    def __init__(self, redir, operation):
93        self.redir = redir
94        self.operation = operation
95        self.tk = redir.tk
96        self.orig = redir.orig
97        self.tk_call = self.tk.call
98        self.orig_and_operation = (self.orig, self.operation)
99
100    def __repr__(self):
101        return "OriginalCommand(%r, %r)" % (self.redir, self.operation)
102
103    def __call__(self, *args):
104        return self.tk_call(self.orig_and_operation + args)
105
106
107def main():
108    root = Tk()
109    root.wm_protocol("WM_DELETE_WINDOW", root.quit)
110    text = Text()
111    text.pack()
112    text.focus_set()
113    redir = WidgetRedirector(text)
114    global previous_tcl_fcn
115    def my_insert(*args):
116        print "insert", args
117        previous_tcl_fcn(*args)
118    previous_tcl_fcn = redir.register("insert", my_insert)
119    root.mainloop()
120    redir.unregister("insert")  # runs after first 'close window'
121    redir.close()
122    root.mainloop()
123    root.destroy()
124
125if __name__ == "__main__":
126    main()
127