Get Model instance from Form without saving

Let say I have a dja开发者_如何学编程ngo ModelForm which I want to edit before saving.

For example,

Instead of this

model_instance = form.save()

I would like to do something like this

model_instance = form.get_model()
model_instance.edit() #say add a new field which is not available on form
model_instance.save()

model_instance = form.save(commit=False)

will return you a object of the model without saving to the DB

you can then add value of some field which is not available on form

model_instance.some_field = value
model_instance.save()

Also:

model_instance = form.instance
# edit
model_instance.save()