from WidgetRedirector import WidgetRedirectorfrom Delegator import Delegator class Percolator:     def __init__(self, text):        # XXX would be nice to inherit from Delegator        self.text = text        self.redir = WidgetRedirector(text)        self.top = self.bottom = Delegator(text)        self.bottom.insert = self.redir.register("insert", self.insert)        self.bottom.delete = self.redir.register("delete", self.delete)        self.filters = []     def close(self):        while self.top is not self.bottom:            self.removefilter(self.top)        self.top = None        self.bottom.setdelegate(None); self.bottom = None        self.redir.close(); self.redir = None        self.text = None     def insert(self, index, chars, tags=None):        # Could go away if inheriting from Delegator        self.top.insert(index, chars, tags)     def delete(self, index1, index2=None):        # Could go away if inheriting from Delegator        self.top.delete(index1, index2)     def insertfilter(self, filter):        # Perhaps rename to pushfilter()?        assert isinstance(filter, Delegator)        assert filter.delegate is None        filter.setdelegate(self.top)        self.top = filter     def removefilter(self, filter):        # XXX Perhaps should only support popfilter()?        assert isinstance(filter, Delegator)        assert filter.delegate is not None        f = self.top        if f is filter:            self.top = filter.delegate            filter.setdelegate(None)        else:            while f.delegate is not filter:                assert f is not self.bottom                f.resetcache()                f = f.delegate            f.setdelegate(filter.delegate)            filter.setdelegate(None)  def main():    class Tracer(Delegator):        def __init__(self, name):            self.name = name            Delegator.__init__(self, None)        def insert(self, *args):            print self.name, ": insert", args            self.delegate.insert(*args)        def delete(self, *args):            print self.name, ": delete", args            self.delegate.delete(*args)    root = Tk()    root.wm_protocol("WM_DELETE_WINDOW", root.quit)    text = Text()    text.pack()    text.focus_set()    p = Percolator(text)    t1 = Tracer("t1")    t2 = Tracer("t2")    p.insertfilter(t1)    p.insertfilter(t2)    root.mainloop()    p.removefilter(t2)    root.mainloop()    p.insertfilter(t2)    p.removefilter(t1)    root.mainloop() if __name__ == "__main__":    from Tkinter import *    main()