如何在Google应用引擎中添加Django的模型表单？

I have built a website based on Google App Engine. It includes ten models, doing some simple calculations based on user inputs. Previously, it was coded using Python 2.5 using djangoform.modelform and db.model to handle data. Since Python 2.7 does not support djangoform.modelform, I would like to use django modelform instead. However, during the migration, I met some problems(sever internal error). when I was trying to add a form by Django.forms.Modelform. I have provided my old codes and new one (does not work). My questions are:I have built a website based on Google App Engi