Non-db fields for Django model or admin
I think you can use a none-model class, which wrapper the Model class and have some extra fields, where you can set/get or save to other place
I have a model, which has some fields stored in db. On top of it, I need to implement non-db fields, which would be loaded and saved using a custom API.
Users should interact with the model using the admin interface, Grappelli is used to enhance the standard Django admin.
I am interested in one of the following:

Model virtual fields or properties, where I can override how to read and save custom fields. (Simple python properties won't work with Django admin)
Editable callables for admin (not sure if it is even possible)
Any other means to display and process custom fields in admin, except of creating custom forms and moving the logic into the forms.