When comparing web2py vs Flask, the Slant community recommends Flask for most people. In the question“What are the best backend web frameworks?” Flask is ranked 2nd while web2py is ranked 16th. The most important reason people chose Flask is:
Even though it's pretty minimalistic out of the box, Flask still provides the necessary tools to build a quick prototype for a web app right after a fresh install. With all the main components pretty much packed in the `flask` package, building a simple web app in a single Python file is as easy as it gets.
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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 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 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 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 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 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 Easily extendable
Allows users to easily extend functionality by using external libraries.
Pro Extremely easy to build a quick prototype
Even though it's pretty minimalistic out of the box, Flask still provides the necessary tools to build a quick prototype for a web app right after a fresh install. With all the main components pretty much packed in the
flask package, building a simple web app in a single Python file is as easy as it gets.
Pro Lots of resources available online
Flask is one of the most popular Python web frameworks, if not the most popular one. As such, there's plenty of guides, tutorials, and libraries available for it. A large number of important Python libraries, such as SQLAlchemy have libraries for Flask, which add valuable bindings to make the development process and the integration between these libraries and Flask as easy as possible.
Pro Minimalist without losing power
Flask is very easy to get up and going, with vanilla HTML or with bootstrap pieces. It doesn't take much lines of Python to load Flask to get headers working, etc, and since it's all modular you don't have to have something you don't want in your application.
Pro Very flexible
Flask gives developers a lot of flexibility in how they develop their web applications.
For example, the choice of not having an ORM, but instead choosing one suited to the task, or another area where Flask gives a lot of options to developers is the templating. They can use Jinja2, Flask's default templating language or choose from a number of different templating languages they desire.
Pro Great documentation
The official documentation is very thorough and complete. Everything is explained in-depth and followed by extremely well-explained tutorials that tackle real-world problems.
Con Not Python 3 compatible
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 Not async-friendly
Flask is explicitly not designed to handle async programming.
Con Threadlocals and globals used everywhere
The default way of creating applications in flask makes it hard to use reusable and clean code.
Con Setting up a large project requires some previous knowledge of the framework
Setting up a large project with Flask is not that easy considering how there's no "official" way of doing it. Blueprints are a useful tool in this regard but require some additional reading and are a bit tricky to get right for a beginner.
The lack of some defaults can also be problematic. Having to choose between different libraries for a certain task is never easy, especially if you have never worked with Flask before.