Principles

Python programming typically follows these basic principles:

• Don’t repeat yourself (DRY).
• There should be only one way of doing things.
• Explicit is better than implicit.

web2py fully embraces the first two principles by forcing the developer to use sound software engineering practices that discourage repetition of code. web2py guides the developer through almost all the tasks common in web application development (creating and processing forms, managing sessions, cookies, errors, etc.).

web2py differs from other frameworks with regard to the third principle, which sometimes conflicts with the other two. In particular, web2py does not import user applications, but executes them in a predefined context. This context exposes the Python keywords, as well as the web2py keywords.

To some this may appear as magic, but it should not. Simply, in practice, some modules are already imported without you doing so. web2py is trying to avoid the annoying characteristic of other frameworks that force the developer to import the same modules at the top of every model and controller.

web2py, by importing its own modules, saves time and prevents mistakes, thus following the spirit of “don’t repeat yourself” and “there should be only one way of doing things”.

If the developer wishes to use other Python modules or third-party modules, those modules must be imported explicitly, as in any other Python program.