[Django]-How can i get my object id from a generic update views to use in my form in django 1.1

Your error comes from this line:

vehiprepa = get_object_or_404(VehiPrepa,pk=object_id)

In your model form, you don’t have a object_id.

To solve this problem, refer to the documentation; which states:

Also, a model form instance bound to a model object will contain a
self.instance attribute that gives model form methods access to that
specific model instance.

From that we understand that the bound instance is in self.instance. So, in your model form you need

vehiprepa = self.instance

instead of the get_object_or_404 line.