What is the correct way to override the __dir__ method?

Question

This question is meant to be more about __dir__ than about numpy.

I have a subclass of numpy.recarray (in python 2.7,

Answer 1

1. and 3: Yes your solution is correct. recarray does not define __dir__ simply because the default implementation was okay, so they didn't bother implementing it, and numpy's devs did not design the class to be subclassed, so I don't see why they should have bothered.

   It's often a bad idea to subclass built-in types or classes that are not specifically designed for inheritance, thus I'd suggest you to use delegation/composition instead of inheritance, except if there is a particular reason(e.g. you want to pass it to a numpy function that excplicitly checks with isinstance).

2. No. As you pointed out in python3 they changed the implementation so that there is an object.__dir__, but on other python versions I can't see anything that you can do. Also, again, using recarray with multiple-inheritance is simply crazy, things will break. Multiple-inheritance should be carefully designed, and usually classes are specifically designed to be used with it(e.g. mix-ins). So I wouldn't bother treating this case, since whoever tries it will be bitten by other problems.

   I don't see why you should care for classes that do not have __dict__... since your subclass has it how should it break? When you'll change the subclass implementation, e.g. using __slots__ you could easily change the __dir__ also. If you want to avoid redefining __dir__ you can simply define a function that checks for __dict__ then for __slots__ etc. Note however that attributes can be generated in subtle ways with __getattr__ and __getattribute__ and thus you simply can't reliably catch all of them.