gfk.py

class ContentTypeForeignKey(models.ForeignKey):
    def __init__(self, **kwargs):
        if "choices" in kwargs:
            kwargs["choices"] = self._process_choices(kwargs["choices"])

        # It is possible for `to` to be passed in with **kwargs. Since
        # ContentType is hardcoded in for the `to` arg when calling super(),
        # this can lead to problems.
        if "to" in kwargs:
            del kwargs["to"]

        super(ContentTypeForeignKey, self).__init__(ContentType, **kwargs)

    def _process_choices(self, choices):
        """
        Pass in choices as a tuple of two-tuples as you would for a normal
        choices kwarg. Unlike a normal choices kwarg, the first item is a
        string of the format app_label.model_name.

        For example: `("blog.BlogArticle", "Blog Article")` resolves to the
        BlogArticle model of the blog app.
        """
        processed_choices = ()
        for choice in choices:
            model_str, form_label = choice
            app_label, model = model_str.split(".")
            content_type = ContentType.objects.get(app_label=app_label, model=model.lower())
            processed_choices += ((content_type.pk, form_label),)

        return processed_choices

from south.modelsinspector import add_introspection_rules
add_introspection_rules([], ["^ContentTypeForeignKey"])