python - 排序对象列表python。对象与我正在分类的对象属于不同的类别

Question

我见过类似的问题，但我似乎无法弄明白。我有两个类，我的 Item 类，然后是我的 Receipt 类。在收据中，我有一个 read_file 方法，它逐行读取 .txt 文件，并将其拆分。然后，我将一个 Item 对象附加到我的列表中，这样我就有了一个 Item 对象列表。我试图按价格对这个列表进行排序，但我不断收到“AttributeError: type object 'Item' has no attribute 'price'”我尝试了一些不同的东西，并在 StackOverflow 上查看了类似的答案，但我就是可以'似乎想不通。据我了解，这是因为它正在查看类而不是实例？感谢您提供任何帮助，谢谢。

实际错误如下:

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

还有我的代码:

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()

Answer 1

查看以下代码段:

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

您放入列表的第一件事是类本身，它没有属性 price。属性只在类的实例中传递。相反，您想将列表声明为空:items = []。