gistfile1.py

    @classmethod
    def with_base_model(cls, base_model):
        """
        This returns an MPTTModel CLASS with the given base model.
        Used for linearizing inheritance chains.
        The given model should be abstract.
        """
        if cls is not MPTTModel:
            raise RuntimeError, "with_base_model() must be called on MPTTModel"

        if not issubclass(base_model, models.Model) or not base_model._meta.abstract:
            raise ValueError, "%r is not an abstract model class" % base_model

        # if we try to copy these, things break. They get set up by the metaclass soon.
        to_ignore = ('__dict__', '_meta', '_mptt_meta')

        # copy all attributes and methods from MPTTModel
        class_dict = dict([(att, getattr(cls, att)) for att in dir(cls) if not att in to_ignore])

        # call the metaclass to create our class.
        return MPTTModelBase(cls.__name__, (base_model,), class_dict)