Python personal library microservice

This is a Python port of my Node.js personal library microservice, built with Flask and SQLite. The front end API tests on the home page also use Bootstrap, jQuery, and highlight.js. The API fulfills the following user stories:

1. I can post a title to /api/books to add a book and returned will be the object with the title and a unique _id.
2. I can get /api/books to retrieve an aray of all books containing title, _id, & commentcount.
3. I can get /api/books/{_id} to retrieve a single object of a book containing title, _id, & an array of comments (empty array if no comments present).
4. I can post a comment to /api/books/{_id} to add a comment to a book and returned will be the books object similar to get /api/books/{_id}.
5. I can delete /api/books/{_id} to delete a book from the collection. Returned will be "delete successful" if successful.
6. If I try to request a book that doesn't exist I will get a "no book exists" message.
7. I can send a delete request to /api/books to delete all books in the database. Returned will be "complete delete successful" if successful.