I get that Flask has a lot of the same design patterns that Ruby’s Sinatra has. I suppose if one used a metadata approach to application construction/deployment that you might be able to basically interchange between them.

I did a search hoping to find out the differences between Flask and Tornado. I was rewarded with a page from the the Flask development doc. The contributor was suggesting that one might link or cascade Flask with either Tornado, Gevent, Gunicorn or some other proxy setup.

While mentioning Tornado the contributor says…

Tornado is an open source version of the scalable, non-blocking web server and tools that power FriendFeed. Because it is non-blocking and uses epoll, it can handle thousands of simultaneous standing connections, which means it is ideal for real-time web services. Integrating this service with Flask is a trivial task:

In the deployment section of the doc Flask makes is clear that the built-in webserver is strictly for development. The reasons are probably very similar to Rails’ webrick but in the case of Flask there are no explanations. Nor is there a recommendation just a list of servers.

I recently deployed a Tornado-ZeroMQ bridge in order to increase the transaction throughput. Sitting in front of the Tornado instance is a traditional webserver like apache, lighttpd, nginx. These webservers are serving static content because that is what they do best and the dynamic requests are passed thru. But why would I deploy lighttpd->tornadoweb->flask? There is plenty of room for improvement here but someone transitioning from sinatra to/from flask could be rewarded.

hello world from their respective websites:
(Flask)

from flask import Flask
app = Flask(__name__)

@app.route("/")
def hello():
  return "Hello World!"

if __name__ == "__main__":
 app.run()

(Sinatra)

require 'sinatra' 
get '/hi' do 
  "Hello World!" 
end