[FIXED] How can I dynamically define the list of base classes for a Python class?

Issue

I have a custom Django mixin which should be imported/added to a view class only if some app is installed, e.g.

class MyView(LoginRequiredMixin, CustomMixin, View):
    #                            ^
    #                            this is an optional mixin
    pass

How to achieve this in Django?

Solution

The parameter list passed to a class definition in Python 3 supports all of the features of a function call, meaning you can use *args and **kwargs-style arguments in the class base list:

bases = [LoginRequiredMixin]

if apps.is_installed("some_app"):
    bases.append(CustomMixin)

class MyView(*bases, View):
    ...

Alternatively, you can use a metaclass:

from django.apps import apps

class MixinsMeta(type):
    def __new__(cls, name, bases, namespace, **kwargs):
        # customize the `bases` tuple here..
        return super().__new__(cls, name, bases, namespace)

Then in the view:

class MyView(View, metaclass=MixinsMeta):
    ...

Answered By - Eugene Yarmash