newfile.py

prices = [9, 11, 8, 5, 7, 10]

def buy_and_sell(stock_prices):
    largest_profit = 0
    for i in range(len(stock_prices)):
        for k in stock_prices[i:]:
            if k - stock_prices[i] > largest_profit:
                largest_profit = k - stock_prices[i]
    return largest_profit

print(buy_and_sell(prices))