When comparing Klein vs Falcon, the Slant community recommends Falcon for most people. In the question“What are the best general-purpose Python web frameworks usable in production sites?” Falcon is ranked 8th while Klein is ranked 20th. The most important reason people chose Falcon is:
Falcon is designed entirely around building REST APIs. It achieves this helps a lot with it being lightweight and simple. It also helps developers take some design choices which would otherwise not be possible with a more general-purpose framework,
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro More concurrent requests, more interactivity
The fact that a Klein server is event-driven and non-blocking means that it can start handling a new request while previous requests are still open. This lets you serve more requests from a single process, meaning running multiple servers is now an option to be explored when your site makes it big, rather than a necessity for responsiveness under even modest loads.
Multiple requests per process also gives you flexibility to do things that would be impractical in WSGI-based alternatives like Flask or Bottle, such as keeping a connection to the browser open to send it chat messages or game updates in a Server Sent Event stream.
Pro Built to build REST APIs
Falcon is designed entirely around building REST APIs. It achieves this helps a lot with it being lightweight and simple. It also helps developers take some design choices which would otherwise not be possible with a more general-purpose framework,
Pro Lightweight with minimal dependencies
Falcon is a very lightweight framework. This can be noticed simply by looking at the dependency list: other than the python standard library, six and mimeparse are the only dependencies.
Pro Performance is really awesome
Cons
Con Lacks database integration
Talking to database is a pretty common thing for a web application to do. Larger frameworks know this, and cover it in some detail by the end of the tutorial. In contrast, the Klein documentation is currently silent on this topic, leaving the issue of how to do database queries in a way that won't block your event-driven code entirely up to you.
Con Limited in scope
Being designed around building REST APIs and the fact that it's minimalistic with very few dependencies makes Falcon opinionated (you should build a REST API) and limited in scope (you shouldn't be using Falcon to build a news site, blog or ecommerce platform).