ID 303883 - GafferThree: Error when subclassing both `GroupPackage` and `LightFilterPackage`

Problem summary:

Customers may wish to create a customized light filter class that supports child packages. This should be possible by inheriting from GroupPackage and LightFilterPackage, but due to an issue with the order of inheritance of GroupPackage / LightFilterPackage, such a class definition results in a TypeError.

Steps to reproduce:

Run the following code in the Python tab:

from Katana import Pluginsimport PackageSuperToolAPIGroupPackage = PackageSuperToolAPI.Packages.GroupPackageLightFilterPackage = Plugins.GafferThreeAPI.PackageClasses.LightFilterPackageclass CustomLightFilterPackage(LightFilterPackage, GroupPackage):    pass

Expected behaviour:

The code runs without errors

Actual behaviour:

A TypeError is raised:

File "<string>", line 7, in <module>    class CustomLightFilterPackage(LightFilterPackage, GroupPackage):TypeError: Error when calling the metaclass bases    Cannot create a consistent method resolution order (MRO) for bases Mixin, Package

Workaround:

No known workaround.

Reproduced versions/platforms:

• 2.5v1
• 2.6v3

Customer version/platform:

Not supplied