Python/Django - Where do I have to make methods that perform like DML?
A common philosophy in Django is "fat models, thin views", so preferably you would put as much of this DML functionality as functions on your model classes. Since models.py already defines the structure of your data, it makes sense to put functions that manipulate your data in the same file as much as possible.
'Methods that perform like DML' means methods that change data in the database.
Is there a standard or guideline for that?
Below are my own guesses.

Collect all functions in file of which name is like 'data_access.py'
Contain functions in each class of models.py
There is no standard. No one will blame even if I make them in views.py
Above all are wrong.