organizing-streamlit-code

To structure a Streamlit app for multiple pages, use a main `streamlit_app.py` file, an `app_pages` folder for page-specific UI, and a `utils` folder for data processing and API helpers to ensure separation of concerns.

You should split Streamlit code into multiple modules when your application requires multiple pages, shared utilities, or testing of business logic outside the UI, transitioning from a monolithic script to a maintainable directory layout.

Streamlit apps avoid the `if __name__ == "__main__"` guard in UI files because Streamlit manages the execution loop itself. You should place this guard only in utility modules to allow testing of business logic outside the UI.

The best way to separate business logic from Streamlit UI components is by creating a standard directory layout that isolates UI modules in an `app_pages` folder and places data processing helpers in a dedicated `utils` folder.

Yes, you can test Streamlit application business logic outside the UI by separating logic modules into a `utils` folder and using the `if __name__ == "__main__"` guard within those utility modules for direct execution and testing.