Why am I getting this output? (Shopping Cart Program)-CodePudding

Current Code Snippet:

for x in range(len(cart) 1):
    if book[int(bookInput)- 1][1] in cart:
        cart[x][0] =1
    else:
        cart.append([1,book[int(bookInput)- 1][0],book[int(bookInput)- 1][1]])

Current Output:

[[1, 'The Lincoln Highway', 30.0], [1, 'The Lincoln Highway', 30.0], [1, 'The Lincoln Highway', 30.0]]
[[1, 'The Lincoln Highway', 30.0], [1, 'The Lincoln Highway', 30.0], [1, 'The Lincoln Highway', 30.0]]
[[1, 'The Lincoln Highway', 30.0], [1, 'The Lincoln Highway', 30.0], [1, 'The Lincoln Highway', 30.0]]

Output desired:

    [[2, 'The Lincoln Highway', 30.0]]

I'm creating a counter for each item to prevent duplicates from being added to the shopping cart list. Been banging my head against my keyboard for days and I can't figure this out! It doesn't recognize that the item is already in the cart.

CodePudding user response：

You're checking if string 'The Lincoln Highway' is the list of entries (lists) e.g. [1, 'The Lincoln Highway', 30.0] so that's why your check fails

added = False # so we know whether to add a new entry at the end
for i in cart:
    if book[int(bookInput)- 1][1] == i[1]: 
        i[0]  = 1
        added = True
        break
if not added:
    cart.append([1,book[int(bookInput)- 1][0],book[int(bookInput)- 1][1]])

Even better, would be to implement cart as set/dict since you will be checking membership quite often e.g.

cart = { "book" : (quantity, price)}
if book in cart: 
    q, p = cart[book]
    cart[book] = (q 1, p)

or similar.

CodePudding user response：

The else: shouldn't be on the if statement. That will cause you to add a new item to the cart for every existing item that doesn't match the current book.

Use the else: clause of the for loop. This executes if the loop runs to completion. Then inside the loop, use break to stop early if you find the matching book.

title = book[int(bookInput)-1][0]
for item in cart:
    if item[1] == title:
        item[0]  = 1
        break
else:
    cart.append([1, title, book[int(bookInput)-1][1]