1 files changed, 175 insertions, 0 deletions
diff --git a/Lib/idlelib/redirector.py b/Lib/idlelib/redirector.py
new file mode 100644
index 0000000000..ec681de38d
--- /dev/null
+++ b/Lib/idlelib/redirector.py
@@ -0,0 +1,175 @@
+from tkinter import TclError
+
+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.  For one thing, we want
+    a text.insert call in idle code to have the same effect as a key press.
+
+    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.  We will also intercept method calls on the tkinter class
+    instance that represents the tk widget.
+
+    In IDLE, WidgetRedirector is used in Percolator to intercept Text
+    commands.  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):
+        '''Initialize attributes and setup redirection.
+
+        _operations: dict mapping operation name to new function.
+        widget: the widget whose tcl command is to be intercepted.
+        tk: widget.tk, a convenience attribute, probably not needed.
+        orig: new name of the original tcl command.
+
+        Since renaming to orig fails with TclError when orig already
+        exists, only one WidgetDirector can exist for a given 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 "%s(%s<%s>)" % (self.__class__.__name__,
+                               self.widget.__class__.__name__,
+                               self.widget._w)
+
+    def close(self):
+        "Unregister operations and revert redirection created by .__init__."
+        for operation in list(self._operations):
+            self.unregister(operation)
+        widget = self.widget
+        tk = widget.tk
+        w = widget._w
+        # Restore the original widget Tcl command.
+        tk.deletecommand(w)
+        tk.call("rename", self.orig, w)
+        del self.widget, self.tk  # Should not be needed
+        # if instance is deleted after close, as in Percolator.
+
+    def register(self, operation, function):
+        '''Return OriginalCommand(operation) after registering function.
+
+        Registration adds an operation: function pair to ._operations.
+        It also adds a widget function attribute that masks the tkinter
+        class instance method.  Method masking operates independently
+        from command dispatch.
+
+        If a second function is registered for the same operation, the
+        first function is replaced in both places.
+        '''
+        self._operations[operation] = function
+        setattr(self.widget, operation, function)
+        return OriginalCommand(self, operation)
+
+    def unregister(self, operation):
+        '''Return the function for the operation, or None.
+
+        Deleting the instance attribute unmasks the class attribute.
+        '''
+        if operation in self._operations:
+            function = self._operations[operation]
+            del self._operations[operation]
+            try:
+                delattr(self.widget, operation)
+            except AttributeError:
+                pass
+            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 colorizer.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:
+    '''Callable for original tk command that has been redirected.
+
+    Returned by .register; can be used in the function registered.
+    redir = WidgetRedirector(text)
+    def my_insert(*args):
+        print("insert", args)
+        original_insert(*args)
+    original_insert = redir.register("insert", my_insert)
+    '''
+
+    def __init__(self, redir, operation):
+        '''Create .tk_call and .orig_and_operation for .__call__ method.
+
+        .redir and .operation store the input args for __repr__.
+        .tk and .orig copy attributes of .redir (probably not needed).
+        '''
+        self.redir = redir
+        self.operation = operation
+        self.tk = redir.tk  # redundant with self.redir
+        self.orig = redir.orig  # redundant with self.redir
+        # These two could be deleted after checking recipient code.
+        self.tk_call = redir.tk.call
+        self.orig_and_operation = (redir.orig, operation)
+
+    def __repr__(self):
+        return "%s(%r, %r)" % (self.__class__.__name__,
+                               self.redir, self.operation)
+
+    def __call__(self, *args):
+        return self.tk_call(self.orig_and_operation + args)
+
+
+def _widget_redirector(parent):  # htest #
+    from tkinter import Toplevel, Text
+
+    top = Toplevel(parent)
+    top.title("Test WidgetRedirector")
+    x, y = map(int, parent.geometry().split('+')[1:])
+    top.geometry("+%d+%d" % (x, y + 175))
+    text = Text(top)
+    text.pack()
+    text.focus_set()
+    redir = WidgetRedirector(text)
+    def my_insert(*args):
+        print("insert", args)
+        original_insert(*args)
+    original_insert = redir.register("insert", my_insert)
+
+if __name__ == "__main__":
+    import unittest
+    unittest.main('idlelib.idle_test.test_redirector',
+                  verbosity=2, exit=False)
+
+    from idlelib.idle_test.htest import run
+    run(_widget_redirector)