Sorting List of Objects python. Objects are of different class than the one I'm sorting in

Question

I've seen similar questions but I just can't seem to figure this out. I have two classes, my Item class, and then my Receipt class. In Receipt I have a method read_file that reads a .txt file line by line, splitting it. I then append an Item object onto my list such that I have a list of Item objects. I'm trying to sort this list by price but I keep getting "AttributeError: type object 'Item' has no attribute 'price'" I've tried a few different things, and looked at similar answers on StackOverflow but I just can't seem to figure it out. From what I understand it's because it's looking at the class instead of the instance? Any help is appreciated, thank you.

The actual error is as follows:

Error message : items.sort(key=operator.attrgetter('price'),reverse=False)
AttributeError: type object 'Item' has no attribute 'price'

And my code:

import operator
import sys
class Item(object):
    def __init__(self, category, name, quantity, price):
        self.category = category
        self.name = name
        self.quantity = quantity
        self.price = price

    def getPrice(self):
        return self.price;

class Receipt(object):
    def __init__(self):
        pass

    def read_file(self):
        with open('grocery.txt') as file:
            items = [Item]
            for line in file:
                c,n,q,p = line.rstrip('\n').split(" ")
                items.append(Item(c,n,q,float(p)))
        return items

    def ask_receipt_format(self):
        answer = input("How would you like this receipt printed? (P for by price, C for by category, A for alphabetical order)")

        if answer.capitalize() == 'P':
            answer = 'P'
        elif answer.capitalize() == 'C':
            answer = 'C'
        elif answer.capitalize() == 'A':
            answer = 'A'
        else:
            print("You must choose a valid receipt format!\n")
            self.ask_receipt_format()
        return answer

    def calculate_total(self):
        pass

def print_bill(self, receipt_format,items):

    if receipt_format == 'P':
        print("Receipt by price")
        print("Category    Item            Quantity    Price    Sub-Total")
        items.sort(key=operator.attrgetter('price'),reverse=False)
        for n in range(len(items)):
            print("{:d} {0:4} {:d} {:4d} {:5d}".format(items[n].category,items[n].name,items[n].quantity,items[n].price, float(items[n].quantity) * float(items[n].price)))




def API(self):
    self.print_bill(self.ask_receipt_format(),self.read_file())


def main():
    receipt = Receipt()
    receipt.API()


if __name__ == "__main__":
    main()

Please include the error message as text - embedding images like you have harms readability and searchability. — Shadow
– Shadow, Commented Feb 13, 2018 at 23:37

John Kugelman · Accepted Answer · 2018-02-14 00:31:51Z

4

Looking at this following snippet:

def read_file(self):
    with open('grocery.txt') as file:
        items = [Item]

The first thing you put in the list is the class itself, which doesn’t have the attribute price. Attributes are only passed on within instances of the class. Instead, you want to declare the list as empty: items = [].

edited Feb 14, 2018 at 0:31

John Kugelman

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answered Feb 13, 2018 at 23:46

Guy

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