__init__ in class based views, use case, anti-pattern

Using Django Forms & APIs
1

Hi,

I’m struggling to find information about when, and especially to be able to answer when not to override the __init__ method of a class based view (CBV). I could not find anything in the forums, all the post are related to the forms.

Is there a good use case when you would like to override __init__ in a CBV to add specific things?

How would you describe the anti-pattern of overriding __init__?

To be short, it has been used only to avoid passing arguments to methods in the CBV (too many).

2

Not that I have ever encountered. Anything I’ve needed to do to change the behavior of a CBV has been able to be done in one of the other methods in the class.

I’m not sure it is an anti-pattern, I’ve just never seen the need. Nor have I ever encountered a case where it was done.

Please clarify.

In most cases, methods like get, get_queryset, get_context_data, etc, work with attributes assigned to the class instance. Any method can add data to that instance for subsequent methods to access.

For example, in DetailView, the get method calls get_object, storing the result in self.object. All other methods within that view then can access self.object.

I don’t see how overriding __init__ would provide any benefit here.

3

The code I stumbled upon was something like:

class MyViewSet:

    def __init__(self, *args: Any, **kwargs: Any):
        self.data = {}
        self.valid = False
        self.reference_user = None
        # many more variables set

    def get_from_things(self, request: Request) -> Response:
        # set things
        do_something()
        process_more()

    def do_something(self):
        # Use variables defined in __init__
        self.valid = ...
        self.reference_user = ...

    def process_more(self):
        # Do more things with the vars from __init__
        if self.valid:
        ...

It’s about declaring local variables in the __init__ (local because Django creates a new class instance for each request) to be used in many methods of the CBV intead of passing around those variables as method’s arguments.

4

The as_view method (which is the starting point for all CBVs), calls setup.

I would override setup to include this data. That seems to me to be the more appropriate place to do this.