How can I sort a list of Python class instances using a specific key?

Question

I need to sort this list of instances using the third value which represents the XP. My function creates an instance of the CodeFighter class using CodeFighter(*codefighter) and I'm not sure how I can sort this without returning a value??

These are the values I'm using to create the instances:

[["Warrior", "1", "1050"], ["Ninja!", "21", "995"], ["Recruit", "3", "995"]]

def sortCodefighters(codefighters):
    res = [CodeFighter(*codefighter) for codefighter in codefighters]
    res.sort(reverse=True)
    return list(map(str, res))

class CodeFighter:
    def __init__(self,name,id,xp):
        self.name=name
        self.id=int(id)
        self.xp =int(xp)
    ??????

This question is similar to a problem in codefights.com website! What is the point, really? At least try and phrase your own question instead of copying and pasting the problem from another website! — jrook
– jrook, Commented Sep 18, 2017 at 3:04
BTW, The question (meant to teach classes in Python) intended the user to opt for something in the lines of __lt__() operator. — jrook
– jrook, Commented Sep 18, 2017 at 3:16

Alan Kavanagh · Accepted Answer · 2017-09-06 14:00:29Z

1

'Your class doesnt need to return a value, it needs an attribute which it can use for sorting. In your case you want to use the 'XP' value to sort. You can use the operator class to sort the classes using the attribute 'XP':

import operator


class CodeFighter:
    def __init__(self,name,id,xp):
        self.name=name
        self.id=int(id)
        self.xp =int(xp)

    def __str__(self):
        return 'Name: %s, ID: %s, XP: %s' % (self.name, self.id, self.xp)


def sortCodefighters(codefighters, reversed=False):
    res = [CodeFighter(*codefighter) for codefighter in codefighters]
    return sorted(res, key=operator.attrgetter('xp'), reverse=reversed)


fighters = [["Warrior", "1", "1050"], ["Ninja!",  "21", "965"], ["Recruit", "3", "995"]]
fighters = sortCodefighters(fighters, reversed=True)
for fighter in fighters:
    print(fighter)

>> Name: Warrior, ID: 1, XP: 1050
>> Name: Recruit, ID: 3, XP: 995
>> Name: Ninja!, ID: 21, XP: 965

and if you flip the reversed value when calling your sortCodefighters function:

fighters = [["Warrior", "1", "1050"], ["Ninja!",  "21", "965"], ["Recruit", "3", "995"]]
fighters = sortCodefighters(fighters, reversed=False)
for fighter in fighters:
    print(fighter)

>> Name: Ninja!, ID: 21, XP: 965
>> Name: Recruit, ID: 3, XP: 995
>> Name: Warrior, ID: 1, XP: 1050

edited Sep 6, 2017 at 14:00

answered Sep 6, 2017 at 13:34

Alan Kavanagh

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2 Comments

Avo Asatryan Over a year ago

TypeError: unorderable types: CodeFighter() < CodeFighter()

Alan Kavanagh Over a year ago

Python3: ideone.com/BHcxJ9 Python2: ideone.com/znBZnT

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