Self Referencing Class Definition in python

Try this:

class Plan(SiloBase):
    cost = DataField(int)
    start = DataField(System.DateTime)
    name = DataField(str)
    items = DataCollection(int)

Plan.subPlan = ReferenceField(Plan)

OR use __new__ like this:

class Plan(SiloBase):

    def __new__(cls, *args, **kwargs):
        cls.cost = DataField(int)
        cls.start = DataField(System.DateTime)
        cls.name = DataField(str)
        cls.items = DataCollection(int)
        cls.subPlan = ReferenceField(cls)
        return object.__new__(cls, *args, **kwargs)