py: Make dir report instance members

[dhylands]

There currently doesn't seem to be any way to get a list of the instance variables. CPython reports this using dir(obj).

I'd like to be able to do something like:

regs = [isinstance(obj, Register) for obj in dir(self)]

[stinos]

+1 since I've had a similar patch lying around for a while now, though for me it's more useful to have __dict__ instead of dir - then again I'm not sure how useful this is for anyone else.. stinos@c1ebef2

[pfalcon]

@stinos : I wanted to tell you for a while: feel free to wrap it config define and submit. I was against adding it myself with the idea that it's useful mostly for initial stages of development, and that can be done on cpython instead, and then run on upy. But that doesn't work that well in practice - we have bunch of unsupported things, and bugs still too, so if an app is intended to be run on upy, it makes sense to develop it incrementally on upy too, and then __dict__ is useful.

[stinos]

config define

@pfalcon the MICROPY_CPYTHON_COMPAT one, or a new one?

[pfalcon]

I had in mind a separate option, but starting with MICROPY_CPYTHON_COMPAT should be good enough.

[dhylands]

@stinos I'd be just as happy with dunder dict as using dir.

[dpgeorge]

I think this is a good addition (independent of #1757). For example, microbit users were asking for this feature.

[pfalcon]

Merged, thanks!