| import string | 
 |  | 
 | class History: | 
 |  | 
 |     def __init__(self, text): | 
 |         self.text = text | 
 |         self.history = [] | 
 |         self.history_prefix = None | 
 |         self.history_pointer = None | 
 |         text.bind("<<history-previous>>", self.history_prev) | 
 |         text.bind("<<history-next>>", self.history_next) | 
 |  | 
 |     def history_next(self, event): | 
 |         self.history_do(0) | 
 |         return "break" | 
 |  | 
 |     def history_prev(self, event): | 
 |         self.history_do(1) | 
 |         return "break" | 
 |  | 
 |     def history_do(self, reverse): | 
 |         nhist = len(self.history) | 
 |         pointer = self.history_pointer | 
 |         prefix = self.history_prefix | 
 |         if pointer is not None and prefix is not None: | 
 |             if self.text.compare("insert", "!=", "end-1c") or \ | 
 |                self.text.get("iomark", "end-1c") != self.history[pointer]: | 
 |                 pointer = prefix = None | 
 |         if pointer is None or prefix is None: | 
 |             prefix = self.text.get("iomark", "end-1c") | 
 |             if reverse: | 
 |                 pointer = nhist | 
 |             else: | 
 |                 pointer = -1 | 
 |         nprefix = len(prefix) | 
 |         while 1: | 
 |             if reverse: | 
 |                 pointer = pointer - 1 | 
 |             else: | 
 |                 pointer = pointer + 1 | 
 |             if pointer < 0 or pointer >= nhist: | 
 |                 self.text.bell() | 
 |                 if self.text.get("iomark", "end-1c") != prefix: | 
 |                     self.text.delete("iomark", "end-1c") | 
 |                     self.text.insert("iomark", prefix) | 
 |                 pointer = prefix = None | 
 |                 break | 
 |             item = self.history[pointer] | 
 |             if item[:nprefix] == prefix and len(item) > nprefix: | 
 |                 self.text.delete("iomark", "end-1c") | 
 |                 self.text.insert("iomark", item) | 
 |                 break | 
 |         self.text.mark_set("insert", "end-1c") | 
 |         self.text.see("insert") | 
 |         self.text.tag_remove("sel", "1.0", "end") | 
 |         self.history_pointer = pointer | 
 |         self.history_prefix = prefix | 
 |  | 
 |     def history_store(self, source): | 
 |         source = string.strip(source) | 
 |         if len(source) > 2: | 
 |             self.history.append(source) | 
 |         self.history_pointer = None | 
 |         self.history_prefix = None | 
 |  | 
 |     def recall(self, s): | 
 |         s = string.strip(s) | 
 |         self.text.tag_remove("sel", "1.0", "end") | 
 |         self.text.delete("iomark", "end-1c") | 
 |         self.text.mark_set("insert", "end-1c") | 
 |         self.text.insert("insert", s) | 
 |         self.text.see("insert") | 
 |  |