def generate_report(book_url):
    """
    Generates the report HTML.
    """
    with piecash.open_book(book_url, readonly=True, open_if_lock=True) as book:
        accounts = [acc.fullname for acc in book.accounts]

        return f"""<html>
        <body>
            Hello world from python !<br>
            Book : {book_url}<br>
            List of accounts : {accounts}
        </body>
        </html>"""
Generates the report HTML.