Ouput is incorrect (list not sorted)

Question

The program takes as input a data-set of orders where id, t selection and t shipping are of type unsigned int, n is the number of orders, and a space character. id1, t selection1, t shipping1; ...; idn, t selectionn, t shippingn . The expected output is a space-separated list of the ids, sorted by t selection + t shipping and terminated by a newline .

Input: 1, 500, 100; 2, 700, 100; 3, 100, 100; 4, 50, 50

Output: 4 3 1 2

My output however shows this

output: 4 1 2 3

Could somebody help me fix this? thanks in advance. below you can see my code. in the code there are some annotations from my teacher btw, don't mind them.

    #!/usr/bin/env python3
    import sys


    class Order:
        def __init__(self, id: int, selection_time: int, shipping_time: int):
            self.id: int = id
            self.selection_time: int = selection_time
            self.shipping_time: int = shipping_time

            '''
            Remove me if you don't need me.
            Add a method to assign to me.
            '''
            self.next: Order = None

        '''
        Make your life easier and your code prettier, use `Operator Overloading`.
        '''


    def sort(data):
        sorted_order = selection_t + shipping_t
        for i in range(len(data)):
            for j in range(i + 1, len(data)):
                if sorted_order[i] > sorted_order[j]:
                    data[i], data[j] = data[j], data[i]
        return data


    if __name__ == '__main__':
        '''
        Retrieves and splits the input
        '''
        data = input()
        data = data.split('; ')

        for d in data:
            id, selection_t, shipping_t = d.split(', ', 2)
            order: Order = Order(int(id), int(selection_t), int(shipping_t))

        sort(data)
    for order.id in data:
        sys.stdout.write(order.id[0])
        sys.stdout.write(" ")

Edo Akse · Answer

as pointed out by Matt, you're not actually using the Order class. Funny thing about classes is that they have a number of so-called magic methods (that naming is very correct)

The magic method that is useful to you in this case is __lt__. This is an abbreviation for Lesser Than. Google search

If you set up this magic method for the class, you can simply call sort on a list containing only instances of that class.

If you do not want to use this magic method, the other option is to use a lambda to tell the sort method how to sort the list. This is very well explained here.

(also, I removed the sys.stdout and replaced it with the standard print)

#!/usr/bin/env python3


class Order:
    def __init__(self, id: int, selection_time: int, shipping_time: int):
        self.id: int = id
        self.selection_time: int = selection_time
        self.shipping_time: int = shipping_time
        self.sort_value: int = shipping_time + selection_time

    def __lt__(self, other) -> bool:
        return self.sort_value < other.sort_value


if __name__ == "__main__":
    data = "1, 500, 100; 2, 700, 100; 3, 100, 100; 4, 50, 50"
    data = data.split("; ")
    order_list = []
    order_list_lambda = []
    for d in data:
        id, selection_t, shipping_t = [int(s) for s in d.split(", ")]
        order: Order = Order(id, selection_t, shipping_t)
        order_list.append(order)
        order_list_lambda.append(order)

    print("using __lt__ class magic method")
    order_list.sort()
    for order in order_list:
        print(order.id)
    print("-----")
    print("using lamda")
    order_list_lambda.sort(key=lambda x: x.sort_value)
    for order in order_list_lambda:
        print(order.id)

output

using __lt__ class magic method
4
3
1
2
-----
using lamda
4
3
1
2

Ouput is incorrect (list not sorted)

1 Answers