When developing a website in Python, you must make a number of decisions. What framework to use is one: will it be the extremely lightweight approach of Werkzeug or Bottle to the big heavyweights such as Django or Turbogears? Will it process requests using the simple synchronous threads or take advantage of asynchronous approaches like Tornado or aiohttp? These are all important decisions that will effect how you write the code and limit you in some crucial ways. But what about the WSGI layer?