[Discussion] Make has_lengthscale an attr rather than kwarg

Currently has_lengthscale is passed in as an argument to kernels.Kernel. Would this not make more sense as a class attribute which can then be overridden by child classes? I can’t think of situation in which it would make sense to allow a user to specify this via a kwarg…

Example proposed implementation:

class Kernel(...):
    _has_lengthscale = False

class RBFKernel(Kernel):
    _has_lengthscale = True

[gpleiss]

@jahall - we thought about creating a StationaryKernel subclass a while back. Since most of our kernels are stationary we thought it was maybe a bit too much overhead. However, I wouldn’t be opposed to adding it into the library.

[jacobrgardner]

Yeah, I think this is a good idea. At the moment, a lot of the Kernel kwargs have turned in to a complete mess to be honest. Most of them are absorbed in to **kwargs in a lot of the subclasses, and there are a huge number of them, so converting some of them to attributes and cleaning up the kwargs sounds like a good thing to do for the next release.