sort objects without native comparison support

example.py

from operator import attrgetter

class User:
    def __init__(self, user_id):
        self.user_id = user_id
    def __repr__(self):
        return 'User({})'.format(self.user_id)

# Example
users = [User(23), User(3), User(99)]
print(users)

# Sort it by user-id
print(sorted(users, key=attrgetter('user_id')))