How to mock out an attribute on an APIView for unit tests in DjangoRestFramework

I have an APIView that hits an external API itself to aggregate results. I've defined it as such:

class SampleView(APIView):
    api = query_api()

    def get(self, request, id):
        result = self.api.query(id)
        return HttpResponse(status=200)

I have a mocked out API to make this testable without having that external API as a dependency in my unit tests. I would like to do something like SampleView.api = fake_api() before running unit tests.

How do I swap out a single attribute like this, in order to replace a concrete class with a mocked out one for unit testing?