Problem with base classes for coordinate-frame classes needing to have name

A recent code change in #11090 is causing errors in SunPy:

astropy/astropy/coordinates/baseframe.py

Lines 289 to 297 in 87df980

    
           # Deal with setting the name of the frame: 
        
           if not hasattr(cls, 'name'): 
        
               cls.name = cls.__name__.lower() 
        
           elif (BaseCoordinateFrame not in cls.__bases__ and 
        
                   cls.name in [base.name for base in cls.__bases__]): 
        
               # This may be a subclass of a subclass of BaseCoordinateFrame, 
        
               # like ICRS(BaseRADecFrame). In this case, cls.name will have been 
        
               # set by init_subclass 
        
               cls.name = cls.__name__.lower()

We have a base class for a frame that does not have a name attribute, so the base.name access produces an error. It's easy enough to add a dummy name attribute to "fix" this on our side, but presumably the Astropy code needs some protection?

Ah, yes, an oversight on my part - oops! I'll submit a follow-up PR now, and add a regression test.

I'm assuming this is RotatedSunFrame? I'm a little confused about why it misses the first if clause then, if it doesn't have a defined name attribute?

The error does not occur directly with our RotatedSunFrame metaframe, but rather when it tries to dynamically create a coordinate frame. For example, RotatedSunFrame can create RotatedSunHeliographicStonyhurst, which has two base classes: the coordinate frame HeliographicStonyhurst and the non-coordinate-frame RotatedSunFrame. The problem is that the latter doesn't have the name attribute.

Astropy's SkyOffsetFrame doesn't have an issue because that metaframe itself subclasses BaseCoordinateFrame, so will automatically have .name. I found that I needed RotatedSunFrame to not subclass BaseCoordinateFrame to work properly, although I don't currently recall why.

Hm. First off, I think that RotatedSunFrame should probably just subclass from BaseCoordinateFrame. I did some experiments with the Sunpy frames to figure out why that was failing before, and I think I now know why. For SkyOffsetFrame, we intentionally do not use the frame-specific representation information from the parent coordinate frame class because we wanted the SkyOffsetFrame to have the same (default) component names as the default representation class. So, for example, a SkyOffsetFrame with an ICRS origin expects lon, lat, distance not ra, dec, distance. But it looks like that is not how you want RotatedSunFrame to work: It looks like your tests expect RotatedSunFrame to have the same component names as the base frame? So, in the construction of the Rotated<framecls>'s in RotatedSunMeta, I think you need to copy the _frame_specific_representation_info from the frame class into members. See sunpy/sunpy#4691 for a possible solution (fingers crossed)

Thanks for fixing the bug in Astropy! Re RotatedSunFrame, I'll continue the discussion in SunPy PR.

Merge pull request #11101 from adrn/coordinates/fix-cls-name

fixed by #11101

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Problem with base classes for coordinate-frame classes needing to have `name` #11096

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	# Deal with setting the name of the frame:
	if not hasattr(cls, 'name'):
	cls.name = cls.__name__.lower()
	elif (BaseCoordinateFrame not in cls.__bases__ and
	cls.name in [base.name for base in cls.__bases__]):
	# This may be a subclass of a subclass of BaseCoordinateFrame,
	# like ICRS(BaseRADecFrame). In this case, cls.name will have been
	# set by init_subclass
	cls.name = cls.__name__.lower()

Problem with base classes for coordinate-frame classes needing to have name #11096

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adrn commented on Nov 27, 2020

adrn commented on Nov 27, 2020

ayshih commented on Nov 27, 2020

adrn commented on Nov 28, 2020

ayshih commented on Nov 29, 2020

mhvk commented on Nov 29, 2020

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Problem with base classes for coordinate-frame classes needing to have `name` #11096