When I started rewriting the API for addons.mozilla.org, my views were mostly the same: get some data and render it as either JSON or XML. I also wanted all my API methods to take an api_version parameter, so I decided class based views would be best. This way my classes could just inherit from a base class.

To do this I had to implement a __call__ method. This works fine, except I wanted to store things into the class – after all the whole point of my use of classes was to keep the code a bit more compact, and cleaner. So, why pass the api_version around everywhere? Unfortunately thread-safety comes to play, and you need a separate instance of your class for each request.

λ

Django’s urlpatterns expects a callable object. So you can’t give it an instance of AddonDetailView(). But you could give it a callable that creates an instance of AddonDetailView() and passes it *args and **kwargs. Luckily python has lambda functions. You can note how we solved that in our urlpatterns.

λ λ

But wrapping all your urls with lambda is tedious and remembering to pass *args and **kwargs is error prone.

So let’s make a lambda function that returns… a lambda function that turns an instance of our class into a callable.

We can now return to coding and not think about thread safety.

λλλ