'Return the price in between the bid and the ask price
:rtype: Price'

def get_mid_price(self, price_wallet_id, quantity_wallet_id):

    ask_price = int(self.get_ask_price(price_wallet_id, quantity_wallet_id))
    bid_price = int(self.get_bid_price(price_wallet_id, quantity_wallet_id))
    return Price(((ask_price + bid_price) / 2), price_wallet_id)
