当我使用以下代码运行迁移时 
ct, created = orm['contenttypes.ContentType'].objects.get_or_create(model='mymodel',     app_label='myapp') 
perm, created = orm['auth.permission'].objects.get_or_create(content_type=ct, codename='mymodel_foo')
我越来越喜欢错误
File "C:\Python26\lib\site-packages\south-0.7.3-py2.6.egg\south\orm.py", line 170, in  __getitem__
raise KeyError("The model '%s' from the app '%s' is not available in this migration." % (model, app))
KeyError: "The model 'contenttype' from the app 'contenttypes' is not available in this migration."
为防止此错误,我修改了代码
from django.contrib.contenttypes.models import ContentType
from django.contrib.auth.models import Permission
class Migration(DataMigration):
    def forwards(self, orm):
        "Write your forwards methods here."
        ct = ContentType.objects.get(model='mymodel', app_label='myapp') 
        perm, created = Permission.objects.get_or_create(content_type=ct, codename='mymodel_foo')
        if created:
            perm.name=u'my permission description'
            perm.save()