Advanced level · Module 4: Building Web APIs with Flask · Lesson 5 of 5

Structuring a Larger Flask Project

Organise a growing Flask application into an application factory and blueprints so it stays maintainable.

In this lesson you will

Create the app with an application factory
Group related routes into blueprints

Key concepts

application factoryblueprintconfiguration objectseparation of concerns

The lesson

A single app.py works for a few routes but becomes hard to manage. An application factory — a create_app() function — builds and configures the app, which makes it easy to create a test version with different settings.

Blueprints group related routes: products, sales and reports each get their own module, registered with the app in create_app().

Keep layers separate: routes handle HTTP, the data-access module handles SQL and validators handle rules. Each layer can then be changed and tested on its own.

Step by step

Move app creation into create_app().
Create a products blueprint and move its routes.
Register the blueprint in the factory.
Update the tests to use create_app() and run them.

Practice activity

Restructure your inventory API into a package with an application factory and two blueprints, keeping all tests passing.

Expected result: A packaged API with unchanged behaviour and a passing test suite.

Check your understanding

How does an application factory help testing?

Show answer
Tests can call create_app() with test settings, such as a temporary database, to get an isolated app instance.

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