【初學python】用python做一個簡單的超市收銀臺付款系統

price=float(input("請輸入商品單價："))
if(price<0):
    print("輸入不合法！")
amount=int(input("請輸入商品數量："))
total_price=price*amount
print(total_price)
if(total_price>=500):
    total_price1 = total_price * 0.8
    print(total_price1)
else:
    total_price1 = total_price
    print(total_price1 )
payment=int(input("請輸入付款金額："))
margin=payment-total_price1
if (margin>0):
    print("找零"+str(margin))
else:
    print("餘額不足！")