class Meta(DeclarativeMeta):

    def __init__(cls, *args, **kw):
        if getattr(cls, '_decl_class_registry', None) is None:
            return
cls.__mapper_args__ = {'polymorphic_identity': cls.__name__}
return super(Meta, cls).__init__(*args, **kw)


class Experiment(Entity, metaclass=Meta):
    pass
Enhance SQLAlchemy syntax for polymorphic identity