Django - Calling one class method from another in Class Based View

Question

I have a method inside a django class based view like called get_player_stats. From this method I want to call another method in the same class but I am unable to. Code is like below:

class ScoreView(TemplateView):

   def get_player_stats(request):
       player_id = request.GET.get(player_id, None)
       # compute  player stats

       #here I want to call like below:
       self.get_team_stats(player_id)

   def get_team_stats(self, player_id):
      #compute team stats

When I run this it says name 'self' is not defined

If I try def get_player_stats(self, request): it says missing 1 required positional argument: 'request'

If I try def get_player_stats(request, self): it says missing 1 required positional argument: 'self'

How can I call get_team_stats from get_player_stats?

This is very frustrating, any help is greatly appreciated

P.S: I call get_player_stats as an ajax call by defining a URL path as below:

url('score/get_player_stats', views.ScoreView.get_player_stats)

Then I call it using $.ajax with url: '/score/get_player_stats'

Answer 1

I see here 2 problems:

1. Misconceptions about class-based views in django
2. Misconceptions about object- and class- methods in python

Let's look in more detail.

1. Django class-based views

It must be sound strange (especially for newcomers) but class-based view in django does not means that you bind methods of objects/classes to url-routes.

More so:

• django.urls.path can use only functions of fn(request, *args, **kwargs)

• Pythonic it's better explicite for self-param makes object-methods unusable for views (at least without "special magic").

So what the meaning of class-based views?

https://github.com/django/django/blob/2bc014750adb093131f77e4c20bc17ba64b75cac/django/views/generic/base.py#L48

In fact it's very simple:

1. class-based view expose class method as_view
2. as_view is a high-order function and not used directly in path/url calls.
3. as_view constructs actual view function at runtime
4. generated function is not very complicated too. Roughly speaking, it looks for existence of defined get/post/put/head-methods, calls them when they exists and raises exceptions when not exists.

So you can see that "one does not simply binds methods of class-view to url-routes in django".

It is a tool that can be hardly recommended for general cases, it works good in cases when this inflexibility is desirable.

2. object-,class-, static- methods

OK. Now the second problem.

Can we call from methods of class-based view other methods?

Yes we can but with some restrictions.

Let's look at one-file demo in django 2.0. (For 1.11 - %s/path/url/g)

from django.urls import path    
from django.http import HttpResponse
from django.utils.decorators import classonlymethod


# CASE 1: normal function - OK
def just_a_fun(request, **kwargs):
    context = kwargs if kwargs else {"method": "just a function"}
    return HttpResponse('method = %(method)s' % context)


class ViewClass(object):
    def get(self, request, **kwargs):
        return just_a_fun(request, **kwargs)

    # CASE 2: Object method - FAIL, not possible to use in `django.url.path`-calls
    def om_view(self, request):
        return self.get(request, **{"method": "object method"})

    # CASE 3: class method - OK
    @classmethod
    def cm_view(cls, request):
        return cls.get(cls, request, **{"method": "class method"})

    # CASE 4: static method - FAIL, not possible to call `cls.get` or `self.get`
    @staticmethod
    def sm_view(request):
        self = None  # This is a problem with static methods
        return self.get(self, request, **{"method": "static method"})

    # CASE 5: HOF-view, similar to django.views.generic.View.as_view - OK
    @classonlymethod
    def as_view(cls, **initkwargs):
        def view(request, **kwargs):
            self = cls(**initkwargs)  # Object construction
            self.request = request
            self.kwargs = kwargs
            return self.get(request, **{"method": "HOF as_view"})

        return view


urlpatterns = [
    path("just-a-fun", just_a_fun),  # OK
    path("object-method",
         ViewClass.om_view),  # Problem: redundant `self` for `path`
    path("class-method", ViewClass.cm_view),  # OK
    path('static-method',
         ViewClass.sm_view),  # Problem: not possible to call `get`
    path('hof-view', ViewClass.as_view()),  # OK. 
]

Summary:

1. Plain functions are best in general
2. Object methods are not usable (at least without some "special magic")
3. Class methods: have no problems. But keep in mind that class methods can use only other class methods
4. Static methods: OK for using in path/url calls but they can't use other methods of classes
5. If you really really want to use OOP: you can do it in "django way" - create HOFs that will generate actual views functions at runtime. Look at django.views.generic source code for inspiration

...

I hope that must clear things up but questions, critique, corrections - you are welcome!