When comparing web2py vs FastAPI, the Slant community recommends FastAPI for most people. In the question“What are the best backend web frameworks?” FastAPI is ranked 4th while web2py is ranked 24th. The most important reason people chose FastAPI is:
It has a simple but powerful dependency injection system, it can be used to handle authentication, per-user rate limiting, authorization controls (e.g. with roles), etc.
Specs
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Pros
Pro Documentation is written in form of a book which is good for beginners
web2py documentation does not follow the common pattern of using Sphinx, MkDocs or ReadTheDocs which is goos for exeperienced developers. Although documentation in form of a book is very easy and good for beginners. Turning web2py the most easy and comprehensive framework to learn and also to teach.
Pro Web2py apps run on GAE, AWS, VPNs, PythonAnywhere, etc
Web2py apps are designed to be portable. With some minor restrictions web2py apps can run on any VPS on SQL databases and/or Mongo, as well as on Google App Engine with the Google Datastore. It is truly code ones and run everywhere. For example at Camio.com we use web2py internally to access a GAE datastore which contains more images than Instagram.
Pro User support
The web2py community is open and friendly and it gives concrete support to newbies and old timers. It's not difficult to get answers from the BDFL Massimo Di Pierro himself.
Pro Maintainable over time
One really positive aspect of web2py application is their maintainability over the years. Old code works even if the framework is updated to the latest version. Not only that, if code is written well it is very short and a new team can pick it up over in little time.
Pro PyCharm supports web2py
While web2py has its own web based IDE which is convenient, it works with WinIDE, PyCharm, and Eclipse. The first two explicitly support web2py. The latter requires some configuration.
Pro Easy to learn without losing any power
web2py is very easy to learn for beginners, yet it has a great deal of power and flexibility as application needs become more complex. It includes an impressively comprehensive set of features, making development very productive without the need to integrate a lot of third-party libraries.
Pro Can be tuned to be really fast in production
The framework is really fast in production after some optimization and fine tuning which can minimize the memory footprint in order to make it run on a really small VPS or slice.
Pro Easily extendable
Allows users to easily extend functionality by using external libraries.
Pro No need to import the API to access the models and controllers context at every request
Models and controllers live in the context of the HTTP request. So the developer does not have to import the API to access this context at every request.
In other words, the models, controllers and templates in web2py use a domain specific language which uses pure web2py syntax and allows to import any module but exposes a few additional objects.
Pro Includes a web-based IDE for creating and managing applications
web2py includes an "admin" app that serves as a web-based IDE for web2py applications. It includes many features, such as application creation, compiling, and packaging; an error ticketing system; a code editor; a debugger; a controller doctest runner; Git and Mercurial integration; and one-click deployment to PythonAnywhere, Google App Engine, and OpenShift.
It is not intended as a full desktop IDE replacement, but it includes some helpful web2py specific functionality and can be convenient for basic editing and debugging tasks and quick prototyping, even for those who primarily work with a more full-featured desktop IDE or editor.
Pro web2py supports the classic editor Vim
Pro Dependency injection
It has a simple but powerful dependency injection system, it can be used to handle authentication, per-user rate limiting, authorization controls (e.g. with roles), etc.
Pro Standards
It is based on standards: OpenAPI, JSON Schema and OAuth 2.0.
Pro Data validation
It validates the data using the types you declared. Even in deeply nested JSON requests.
Pro High-performance
It's based on Starlette and Pydantic, so, it's one of the fastest Python frameworks.
Pro Editor completion
It is based on Python type declarations, so, editors and tools can give great support. Including type checks and autocompletion everywhere.
Pro One of the fastest growing communities
Pro Fast is really fast (!)
It's easy to develop API based applications in Python on deadlines for Android and IOS Development.
Pro Automatic docs
It generates interactive API documentation automatically from your code.
Pro Database independent
It's independent of database or ORM, but compatible with all of them. Including relational databases and NoSQL.
Pro Async IO / optional
It's based on Async IO, which gives it high concurrency. But you can use non-async libraries and it runs them appropriately.
Pro World class documentation
It has some of the best documentation of any framework.
Pro WebSockets
Because it's an async framework, it can handle async-native protocols like WebSockets.
Pro OAuth 2.0
It has integrated support for OAuth 2.0. Including declaring required scopes per endpoint. So, you can easily integrate it with external OAuth 2.0 providers or build your own with it.
Pro Background tasks
Included support for background tasks, thanks to being based on Starlette.
Pro Supports GraphQL
Python's graphene library is included as an optional dependency meaning that GraphQL API's are supported out of the box, with no additional tweaking needed.
Cons
Con Abandoned framework with (almost) no community
Con The web IDE is not a full-featured IDE
web2py includes an "admin" app that serves as a web-based IDE for web2py applications. It includes many features, such as application creation, compiling, and packaging; an error ticketing system; a code editor; a debugger; a controller doctest runner; Git and Mercurial integration; and one-click deployment to PythonAnywhere, Google App Engine, and OpenShift. However, particularly with regard to code editing and debugging and version control integration, it is not as full-featured as some of the more popular desktop IDEs such as PyCharm. So, developers expecting a PyCharm-like experience may be somewhat disappointed. In any case, use of the web-based IDE is completely optional.
Con Smaller community
Since FastAPI is relatively new, its community is smaller than Django Rest Framework. But it can grow with time.