ValueError: View function did not return a response in flask [duplicate]

Answer 1

This question has been answered a few times but it took me a while to understand what I was looking for specific to my (subtly different) problem, so I just want to throw in that the generic answer here is this:

Somewhere in your code, you're defining a route but not returning anything. This code returns a template:

@app.route('/welcome')
def welcome():
    return render_template("welcome.html")

This code only returns a template under some circumstances:

@app.route('/welcome')
def welcome():
    if request.method == "POST":
        return render_template("welcome.html")

So if you're really not sure why you are seeing ValueError: View function did not return a response walk through your code and make sure that all your route definitions (def foo():) actually return something, and that something isn't nested inside of an if clause

It is pretty annoying that the error doesn't give a lot of clues about where it is getting stuck, but I'm sure a more experienced Pythoner could explain why that is.

Answer 2

The log() method does not return a response if you're accessing it via GET. Your question is a bit uninformative where the error is happening, but this is what I can deduce.

Edit: Looking into the video, it is indeed the log method that is causing you trouble. You've accidentally indented too deep.

@app.route('/log', methods=['GET','POST'])
def log():
    error = None
    if request.method == "POST":
        if request.form['username'] != 'admin' or  request.form['password'] != 'admin':
            error = "Invalid credentials"
        else: 
            session['logged_in'] = True
            return redirect (url_for('hello'))
    return render_template('log.html', error=error)