class CreditCard:
    def __init__(self,card_no,balance):
        self.card_no=card_no
        self.balance=balance
 
class Customer:
    def __init__(self,cards):
        self.cards=cards
 
    def purchase_item(self, price, card_no):
        if price < 0:
            raise Exception("Invalid Price")
        if card_no not in self.cards:
            raise Exception("Wrong card")
        if price>self.cards[card_no].balance:
            raise Exception("Wrong card")
card1=CreditCard(101,800)
card2=CreditCard(102,2000)
cards={card1.card_no:card1,card2.card_no:card2}
c=Customer(cards)
 
while(True):
    card_no=int(input("Please enter a card number"))
    try:
        c.purchase_item(1200,card_no)
    except Exception as e:
        if str(e)=="Invalid Price":
            print("Product price is wrong")
            break
        if str(e)=="Wrong card":
            continue

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