Python：用lambda/map处理列表内元组的订单金额计算问题

Hey there! Let's break down what's going wrong and fix this step by step.

The Issue with Your Original Code #

Your current prodcut_price method only processes the first product in each order. That's because the lambda directly references x[1]—the second element of each order sublist—ignoring all other product tuples that come after the store ID in each order.

The Solution #

We need to adjust the method to:

1. Extract every product from all orders (ignoring the store ID in each sublist).
2. Calculate the cost for each individual product, applying the $10 surcharge if the subtotal is under $100.

Here's the corrected Bookshop class with the fixed method:

class Bookshop: 
    def __init__(self): 
        self.orders = 0 
    def prodcut_price(self): 
        # Step 1: Flatten all product tuples from every order (skip store IDs)
        all_products = sum(map(lambda order: order[1:], self.orders), [])
        # Step 2: Calculate cost for each product, add surcharge if needed
        result = list(map(
            lambda prod: (
                prod[0], 
                prod[1] * prod[2] if prod[1] * prod[2] >= 100 else prod[1] * prod[2] + 10
            ),
            all_products
        ))
        return result

# Test the corrected code
x = Bookshop() 
x.orders = [ 
    [1, ("5464", 4, 9.99), ("8274",18,12.99), ("9744", 9, 44.95)], 
    [2, ("5464", 9, 9.99), ("9744", 9, 44.95)], 
    [3, ("5464", 9, 9.99), ("88112", 11, 24.99)], 
    [4, ("8732", 7, 11.99), ("7733", 11,18.99), ("88112", 5, 39.95)] 
] 
r1 = x.prodcut_price() 
print(r1) 

How It Works #

• map(lambda order: order[1:], self.orders): For each order, this returns a list containing only the product tuples (we skip the first element which is the store ID).
• sum(..., []): This flattens all those separate product lists into one single list of all products across orders.
• The second map applies the cost logic to every product:
  • Compute the subtotal as quantity × unit price
  • If the subtotal is $100 or more, keep it; otherwise, add $10 to cover the surcharge.

Expected Output #

When you run the code, you'll get a complete list of all products with their calculated costs:

[('5464', 49.96), ('8274', 233.82), ('9744', 404.55), ('5464', 99.91), ('9744', 404.55), ('5464', 99.91), ('88112', 274.89), ('8732', 93.93), ('7733', 208.89), ('88112', 199.75)]

内容的提问来源于stack exchange，提问作者Mariam Adel