def get_choices(self, include_blank=True, blank_choice=BLANK_CHOICE_DASH):
        first_choice = include_blank and blank_choice or []
        if self.choices:
            return first_choice + list(self.choices)
        rel_model = self.rel.to
        if hasattr(self.rel, 'get_related_field'):
            lst = [(getattr(x, self.rel.get_related_field().attname), smart_unicode(x)) for x in rel_model._default_manager.complex_filter(self.rel.limit_choices_to)]
        else:
            lst = [(x._get_pk_val(), smart_unicode(x)) for x in rel_model._default_manager.complex_filter(self.rel.limit_choices_to)]
        return first_choice + lst
Returns choices with a default blank choices included, for use
dataset/ETHPy150Open AppScale/appscale/AppServer/lib/django-1.2/django/db/models/fields/__init__.py/Field.get_choices