Issue with sorting list of objects

Question

I'm having trouble sorting a list of objects in Python. I have a list of Person objects, and I want to sort them based on their age. However, the sorting doesn't seem to be working as expected. Here's my code:

class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age

people = [
    Person("Alice", 30),
    Person("Bob", 25),
    Person("Charlie", 40),
    Person("David", 22)
]

sorted_people = sorted(people, key=lambda person: person.age)
print(sorted_people)

I expected the output to be a list of Person objects sorted by their age, like this:

[Person("David", 22), Person("Bob", 25), Person("Alice", 30), Person("Charlie", 40)]

However, the actual output I'm getting is:

[<__main__.Person object at 0x...>, <__main__.Person object at 0x...>, ...]

It seems like the sorting is not working as intended. What am I doing wrong? How can I fix this sorting issue?

As far as we can tell that's working exactly as intended. Your output is a list of Person objects, what's makes you think they're not in the right order? — jonrsharpe, Aug 22 '23 at 12:28
Related: [How to print instances of a class using print()?](https://stackoverflow.com/q/1535327/11082165) — Brian61354270, Aug 22 '23 at 12:30

score 3 · Accepted Answer · edited Aug 22 '23 at 12:50

3

Add a __repr__ implementation to your class to get nice default string representations:

class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age

    def __repr__(self):
        return f'Person({repr(self.name)}, {self.age})'

As Kelly Bundy points out, you can also use the !r shorthand in the f-string literal to call repr() on the member items:

class Person:
    # ...
    def __repr__(self):
        return f'Person({self.name!r}, {self.age!r})'

edited Aug 22 '23 at 12:50

Kelly Bundy

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answered Aug 22 '23 at 12:37

Mathias R. Jessen

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Or `f'Person({self.name!r}, {self.age!r})'` – Kelly Bundy Aug 22 '23 at 12:38
@KellyBundy I'm afraid I'm not familiar with the `!r` formatting directive – Mathias R. Jessen Aug 22 '23 at 12:39
It calls `repr()`. – Kelly Bundy Aug 22 '23 at 12:41
@KellyBundy Cheers, added to the answer – Mathias R. Jessen Aug 22 '23 at 12:43

score 0 · Answer 2 · answered Aug 22 '23 at 12:32

The list is probably sorted exactly right!
You are seeing the default representation for a python object.
If you want to see a nicer looking output when printing, look into implementing one of the following "dunder" methods, __str__() or __repr__().
A good Tutorial here.

It might end up looking something like this:

class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age
    def __str__(self):
        return f'Name: {self.name} Age: {self.age}'

Issue with sorting list of objects

2 Answers2