inconsistent use of () and [] for attributes in ModelAdmin class - Also class variables

[Martin Massera]

In Django's ModelAdmin class, most "lists" are initialized as tuples () while two of them (inlines and actions)are initialized as lists []

list_display = ('__str__',)
list_display_links = ()
list_filter = ()
...
list_editable = ()
search_fields = ()
...
inlines = []
...
actions = []

This is inconsistent.

And also since these are declared in the class, they are shared among all instances if this value is not set. This brings the problem where you inadvertedly add a value to a list and this gets added to all Admin instances where this attribute has not been set.

ie: I wanted to add an action to an admin subclass so I did MyAdmin.actions.append('some_action') which added this action to all my admins who had not set a new value to actions.

While lists are more semantically correct than tuples, tuples have the advantage of being immutable, so they force users to reset the value every time.

So, two solutions:

• declare all these attributes as instance variables in the constructor. Possibly setting them all as lists
• declare all these attributes as tuples, keeping them where they are

[Carlton Gibson]

OK, I think this needs to go to the DevelopersMailingList.

There was some movement towards lists (not necessarily in these exact locations) in #30947 and ​PR 11267.

The idea was the homogenous lists should lists, where other iterables where the fields were of different kinds should use tuples.

(I defer the question of which applies where in the case raised here.)

And also since these are declared in the class, they are shared among all instances if this value is not set.
...
While lists are more semantically correct than tuples, tuples have the advantage of being immutable, so they force users to reset the value every time.

This seems more pressing. ​Claude raise this worry in the discussion on the commit for the PR 11267

... I think we should consider the impact on mutability too. Don't we get a new risk here where people might suddenly change a class-level list ...

I'm not sure what the best way to balance the considerations is, but I think it's worth asking for input.

[Carlton Gibson]

I'll mark this needs info pending a discussion.