如何修复“UnboundLocalError：赋值前引用的局部变量‘books’”？

Question

I'm new to python and currently trying to display data from my database to my homepage but I am getting the above named error.

I'm running Python 3.7. I've tried setting 'books' as a global variable but I end up with a different Name error [Name "books" not defined].

    @app.route("/", methods=["GET", "POST"])
    def home():
        if request.form:
            book = Book(title=request.form.get("title"))
            db.session.add(book)
            db.session.commit()
            books = Book.query.all()
        return render_template("home.html", books=books)

I expect when a user loads the home page, all books currently in the database are displayed in a form but instead I get the above error(s).

Answer 1

Change your code to this

@app.route("/", methods=["GET", "POST"])
def home():
    books = {}
    if request.form:
        book = Book(title=request.form.get("title"))
        db.session.add(book)
        db.session.commit()
        books = Book.query.all()
    return render_template("home.html", books=books)

And let me know what happens