'Return the minimum price that a tick is listed for on this side of the order book
:rtype: Price'

def get_min_price(self, price_wallet_id, quantity_wallet_id):

    key = (price_wallet_id, quantity_wallet_id)
    if ((key in self._depth) and (self._depth[key] > 0)):
        return self.get_price_level_list(price_wallet_id, quantity_wallet_id).min_key()
    else:
        return None
