Initialize search prompt

def _init_digit_argument(self, keyinfo):
        """Initialize search prompt
        """
        c = self.console
        line = self.l_buffer.get_line_text()
        self._digit_argument_oldprompt = self.prompt
        queue = self.process_keyevent_queue
        queue = self.process_keyevent_queue
        queue.append(self._process_digit_argument_keyevent)

        if keyinfo.char == "-":
            self.argument = -1
        elif keyinfo.char in u"0123456789":
            self.argument = int(keyinfo.char)
        log(u"<%s> %s"%(self.argument, type(self.argument)))
        self.prompt = u"(arg: %s) "%self.argument
        log(u"arg-init %s %s"%(self.argument, keyinfo.char))