fix hang when adding nested compound attributes

[benblo]

fixes #5

[mottosso]

Should we make the class Fn = None? One of these aren't necessary.

Also try and stick to 80 lines with if possible, which it can be here if we put the comment on the line above.

[benblo]

Good point, removed.

Actually I was wondering if we should keep declaring Fn as currently (static for each attribute type), but always instantiate something like self.Fn = cls.Fn() directly in _AbstractAttribute.__init__(), but I'm not 100% sure this is strictly necessary outside for non-Compound attributes.
Also I'm not sure how to actually get to the type-specific Fn from _AbstractAttribute 😄

[mottosso]

Could we add just one test to this, to make sure it works on all Maya's, and that it won't break again in the future?

[benblo]

I could, though last time I used tests wasn't very fun ;)
I don't really have time to spend on this right now, I tend to work in bursts so next time I can focus on cmdx, I'll do it right, setup the docker thing you mentioned etc and finish this.

Btw, I recently created wrappers for some APIs (eg playbackOptions), that are exposed as commands although to me they are much better suited as a class with properties (all it does is expose get/set accessors).
Much of my pains with Maya come from not having proper autocompletion for cmds, not having proper typing information, and spending way too much time reading the docs to figure out the keyword combinations, so I've now taken the habit of whenever I need a new API, first wrapping it into something I find more sensible (I feel like most of it could be automated).
I don't know if this is of any interest to you? maybe in a different module, since I feel this is not necessarily the focus of cmdx.

[mottosso]

I could, though last time I used tests wasn't very fun ;)

Haha, I understand exactly. xD I've added a test just now.

I don't know if this is of any interest to you? maybe in a different module, since I feel this is not necessarily the focus of cmdx.

Not for cmdx, that's more in the territory of PyMEL I think; i.e. all-encompassing mess. What's keeping you from using that?