Difference between auto_now and auto_now_add
As Official Django documentation says -
auto_now, auto_now_add and default are mutually exclusive and will result in an error if used together
What I understood in Django models field's attributes is  

auto_now - updates the value of field to current time and date every time the Model.save() is called.
auto_now_add - updates the value with the time and date of creation of record.

My question is what if a filed in model contains both the auto_now and auto_now_add set to True? What happens in that case?