When comparing Nagare vs Tornado, the Slant community recommends Tornado for most people. In the question“What are the best general-purpose Python web frameworks usable in production sites?” Tornado is ranked 7th while Nagare is ranked 14th. The most important reason people chose Tornado is:
Tornado can scale to several open connections at the same time. This makes it perfect for applications where performance is very important.
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Pros
Pro Continuation based web framework
Nagare allows for simpler programming flow hiding client/server requests.
Pro 100% Python web application development - no HTML, CSS or JS needed
Nagare is a mature web framework that saves you from manually creating routes. It basically is just a Python object graph.
Pro Designed for performance
Tornado can scale to several open connections at the same time. This makes it perfect for applications where performance is very important.
Pro Amazing asynchronous functionalities
Cons
Con Stateful server that maintains both session and UI states server side
Con Uses old YUI2 JS framework
Nagare uses YUI2 internally for XHR requests. YUI2 has been deprecated since 2011.
Con It's usually useful only when building real-time web applications
Because it's basically a framework for building real-time applications it has great support for things like WebScokets and uses non-blocking I/O. But it lacks in features that are used to build general-purpose websites like blogs, e-commerce sites, web portals etc...
For example it lacks ORM integration (at least out of the box) and it doesn't have a very powerful template engine.