<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def on_decks(self, *args):
 """Inform the cards of their deck and their index within the deck; extend the ``_hint_offsets`` properties as needed; and trigger a layout. """

        if None in (
                self.canvas,
                self.decks,
                self.deck_x_hint_offsets,
                self.deck_y_hint_offsets
        ):
            Clock.schedule_once(self.on_decks, 0)
            return
        self.clear_widgets()
        decknum = 0
        for deck in self.decks:
            cardnum = 0
            for card in deck:
                if not isinstance(card, Card):
                    raise TypeError("You must only put Card in decks")
                if card not in self.children:
                    self.add_widget(card)
                if card.deck != decknum:
                    card.deck = decknum
                if card.idx != cardnum:
                    card.idx = cardnum
                cardnum += 1
            decknum += 1
        if len(self.deck_x_hint_offsets) < len(self.decks):
            self.deck_x_hint_offsets = list(self.deck_x_hint_offsets) + [0] * (
                len(self.decks) - len(self.deck_x_hint_offsets)
            )
        if len(self.deck_y_hint_offsets) < len(self.decks):
            self.deck_y_hint_offsets = list(self.deck_y_hint_offsets) + [0] * (
                len(self.decks) - len(self.deck_y_hint_offsets)
            )
        self._trigger_layout()