Add a few books to your website. You should see them listed on the home page.

Now, stop your server by hitting the stop button in PyCharm:

Then run your server again:

Go to your website and reload the home page. What do you see? What happened to your books?

This is because our books are currently stored in the List all_books, this variable gets re-initialised when we re-run main.py and all the data inside is lost.

If this happened to our user's data, they would not have much faith in our website.

In order to fix this, we need to learn about data persistence and how to work with databases in Flask applications.