We can implement WSGI applications as Callable objects instead of standalone functions. This allows us to have stateful processing in our WSGI server without the potential confusion of global variables. In our previous example, the get_spin() WSGI application relied on two global variables, american and european. The binding between the application and global can be mysterious.

The point of defining a class is to encapsulate the processing and data into a single package. We can use Callable objects to encapsulate our applications in a better manner. This can make the binding between stateful Wheel and WSGI applications clearer. Here is an extension to the Wheel class that makes it into a callable WSGI application:

from collections.abc import Callable
class Wheel2( Wheel, Callable ):
    def __call__(self, environ, start_response):
        winner= self.spin() # 3. Evaluate.
        status = '200 OK' # 4. Respond.
        headers = [('Content-type...