Python - printing object error: object is not subscriptable

Question

messing around with Python and was building a simple text cart thing. when i try to iterate through the cart, using the defined __str__, it give me this error: 'CartItem' object is not subscriptable. i've tried to understand what this was talking about, but have failed to find anything on the matter.

here is the relevant code:

class CartItem:
  def __init__(self, name, price):
    self.name = name
    self.price = price
  def __str__(self):
    print(self.name + " --> " + self.price)
    return "-- item printed --\n"

class Cart:
  def __init__(self):
    self.items = []

  def __str__(self):
    if(len(self.items) > 0):
      index = 0
      for item in self.items:
        print(str(index) + ": " + item[index].name + ' --> ' + item[index].price)
        index += 1
    else:
      print("No Items in Cart")
    return "-- cart items printed--\n"

  def addItem(self, cartItem):
    self.items.append(cartItem)
    print (cartItem.name + ", costing $" + cartItem.price + ", has been added to cart\n")
    print(self.items)  # *should* print out the contents of the cart, but doesn't...

flarn = CartItem("flarn", "200.00")
print(flarn)
userCart = Cart()
userCart.addItem(flarn)
print(userCart)  # if i remove this line, i get [<__main__.CartItem object at 0x....>]??

can someone please explain what that error, 'CartItem' object is not subscriptable, means in context of this code? bonus point if you can explain the output removing print(userCart) returns.

You're both looping over and indexing items in the same loop, `item[index].name`. You don't need `index` and `item` is an item from the list you're looping over, not the list itself. — frippe, Nov 16 '21 at 19:04

buran · Accepted Answer · 2021-11-16T19:37:56.980

The problem is item[index].name - CartItem is not subscriptable as the error states. You don't need to use index, you iterate over list. Also you can simplify your __str__() method.

Note that using print() inside the __str__() method is bad. Better construct a string to describe the cart and return it. Also should have __repr__ instead of __str__() for CartItem. It will be used when you print items in container like list Cart.items. Also you can use the string representation of the Item when you construct the Cart.__str__()

class CartItem:
    def __init__(self, name, price):
        self.name = name
        self.price = price
    def __repr__(self):
        return f'{self.name} --> {self.price}'


class Cart:
    def __init__(self):
        self.items = []

    def __str__(self):
        if self.items:
            return '\n'.join(f'{idx}: {item}' for idx, item in enumerate(self.items))
        return "Empty Cart"

    def addItem(self, cartItem):
        self.items.append(cartItem)
        print(f'{cartItem.name}, costing ${cartItem.price}, has been added to cart')
        print(self.items)  # *should* print out the contents of the cart, but doesn't...


userCart = Cart()
print(userCart)
flarn = CartItem("flarn", "200.00")
print(flarn)
userCart.addItem(flarn)
flarn = CartItem("flarn", "100.00")
print(flarn)
userCart.addItem(flarn)
print(userCart)

output:

Empty Cart
flarn --> 200.00
flarn, costing $200.00, has been added to cart
[flarn --> 200.00]
flarn --> 100.00
flarn, costing $100.00, has been added to cart
[flarn --> 200.00, flarn --> 100.00]
0: flarn --> 200.00
1: flarn --> 100.00

fantastic! thank you. i learned so much from this. wow. i just have one remaining question: what the heck does the error *actually* mean?? can't find anything on `subscriptable`... — WhiteRau, Nov 18 '21 at 20:27
also, the singe line ``for` loop was handy as heck! thanks again. :) — WhiteRau, Nov 18 '21 at 20:30
[What does it mean if a Python object is "subscriptable" or not?](https://stackoverflow.com/q/216972/4046632) — buran, Nov 18 '21 at 21:05
that is [generator expression](https://www.python.org/dev/peps/pep-0289/). Also have a look at e.g. [list comprehension](https://docs.python.org/3/tutorial/datastructures.html#list-comprehensions). There are also dict comprehension and set comprehension — buran, Nov 18 '21 at 21:07

Python - printing object error: object is not subscriptable

1 Answers1