The DatabaseIndex class is accessible via the sqlobject.index module.
Further keys may be added to the column specs in the future.
The class also take the keyword argument unique ; if true then a UNIQUE index is created.
Abstract classes can override this to customize issubclass().
This is invoked early on by abc.ABCMeta.__subclasscheck__(). It should return True, False or NotImplemented. If it returns NotImplemented, the normal algorithm is used. Otherwise, it overrides the normal algorithm (and the outcome is cached).
See the source for more information.