Python: Sort a list of objects based on their attributes

Question

Just to preface this, I've already checked out posts pertaining to this question and they haven't fully answered mine.

So I would just like to know how to sort a list of objects based on their attributes in two ways:

1. if the attribute is a string (to alphabetize)
2. if the attribute is a integer (to do by numerical order)

This is my list of classes:

mainList = [
    hero( name='SirGoose', classes='Fighter', level=150 ),
    hero( name='Conan', classes='Barbarian', level=160 ),
    hero( name='KingArthur', classes='Knight', level=170 )
]

So what I'm really looking for is a way to sort this list to that the hero's names are sorted in alphabetical order, then another method for level. Thank you!

Answer 1

sorted, list.sort accept optional key parameter. Pass a key function. The return value of the function is used for comparison instead of the original value:

>>> from collections import namedtuple
>>> hero = namedtuple('hero', ['name', 'classes', 'level'])
>>>
>>> mainList = [
...     hero(name='SirGoose', classes='Fighter', level=150 ),
...     hero(name='Conan', classes='Barbarian', level=160 ),
...     hero( name='KingArthur', classes='Knight', level=170 )
... ]
>>> sorted(mainList, key=lambda h: (h.name, h.level))
[hero(name='Conan', classes='Barbarian', level=160),
 hero(name='KingArthur', classes='Knight', level=170),
 hero(name='SirGoose', classes='Fighter', level=150)]

NOTE: the key function used here (lambda) returns a tuple. tuples are compared item by item. If the first items are same, the next items are compared, ...

>>> ('SirGoose', 12) < ('Barbarian', 160)
False
>>> ('SirGoose', 12) < ('SirGoose', 160)
True

---

Alternative using operator.attrgetter:

>>> import operator
>>> sorted(mainList, key=operator.attrgetter('name', 'level'))
[hero(name='Conan', classes='Barbarian', level=160),
 hero(name='KingArthur', classes='Knight', level=170),
 hero(name='SirGoose', classes='Fighter', level=150)]