The simplest structural change that can be applied to a module-based Flask application is to transform it into a typical Python package, with special accommodation for the static and templates folders.

application
└──application
    ├──__init__.py
    ├──static
    │  ├──app.js
    │  └──styles.css
    └──templates
         ├──index.html
         └──layout.html

Here, we created a top-level application package, moved the app.py module along with the static and template folders inside it, and renamed it __init__.py.

One detail that should be handled at this point is the code that is used to run the development server. If you recall, the single-module application contained the following conditional statement:

if __name__ == "__main__":
    app.run()

This allows us to execute the module file with the Python interpreter directly, as follows:

$ python app.py
* Running on http://localhost...