Class WidgetRedirector

Lib/idlelib/redirector.py:3–117

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 proce

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):
        ''&#x27;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.
        ''&#x27;
        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):
        w = self.widget
        return f"{self.__class__.__name__,}({w.__class__.__name__}<{w._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.