secret key not set in flask session, using the Flask-Session extension

Right now I am using a flask 3rd party library Flask-Session and I am having no luck getting a session working.

When I connect to my site, I get the following error:

RuntimeError: the session is unavailable because no secret key was set. Set the secret_key on the application to something unique and secret.

Below is my server code.

    from flask import Flask, session
    from flask.ext.session import Session

    SESSION_TYPE = 'memcache'

    app = Flask(__name__)
    sess = Session()

    nextId = 0

    def verifySessionId():
        global nextId

        if not 'userId' in session:
            session['userId'] = nextId
            nextId += 1
            sessionId = session['userId']
            print ("set userid[" + str(session['userId']) + "]")
        else:
            print ("using already set userid[" + str(session['userId']) + "]")
        sessionId = session.get('userId', None)
        return sessionId

    @app.route("/")
    def hello():
        userId = verifySessionId()
        print("User id[" + str(userId) + "]")
        return str(userId)

    if __name__ == "__main__":
        app.secret_key = 'super secret key'

        sess.init_app(app)

        app.debug = True
        app.run()

As you can see, I do set the app secret key. What am I doing wrong?

Are there other session options?

Other info: Running Python 2.7 on Linux Mint

Full paste:

    Traceback (most recent call last):
      File "/home/sean/code/misc/hangman/venv/lib/python2.7/site-packages/flask/app.py", line 1836, in __call__
        return self.wsgi_app(environ, start_response)
      File "/home/sean/code/misc/hangman/venv/lib/python2.7/site-packages/flask/app.py", line 1820, in wsgi_app
        response = self.make_response(self.handle_exception(e))
      File "/home/sean/code/misc/hangman/venv/lib/python2.7/site-packages/flask/app.py", line 1403, in handle_exception
        reraise(exc_type, exc_value, tb)
      File "/home/sean/code/misc/hangman/venv/lib/python2.7/site-packages/flask/app.py", line 1817, in wsgi_app
        response = self.full_dispatch_request()
      File "/home/sean/code/misc/hangman/venv/lib/python2.7/site-packages/flask/app.py", line 1477, in full_dispatch_request
        rv = self.handle_user_exception(e)
      File "/home/sean/code/misc/hangman/venv/lib/python2.7/site-packages/flask/app.py", line 1381, in handle_user_exception
        reraise(exc_type, exc_value, tb)
      File "/home/sean/code/misc/hangman/venv/lib/python2.7/site-packages/flask/app.py", line 1475, in full_dispatch_request
        rv = self.dispatch_request()
      File "/home/sean/code/misc/hangman/venv/lib/python2.7/site-packages/flask/app.py", line 1461, in dispatch_request
        return self.view_functions[rule.endpoint](**req.view_args)
      File "/home/sean/code/misc/session/sessiontest.py", line 27, in hello
        userId = verifySessionId()
      File "/home/sean/code/misc/session/sessiontest.py", line 16, in verifySessionId
        session['userId'] = nextId
      File "/home/sean/code/misc/hangman/venv/lib/python2.7/site-packages/werkzeug/local.py", line 341, in __setitem__
        self._get_current_object()[key] = value
      File "/home/sean/code/misc/hangman/venv/lib/python2.7/site-packages/flask/sessions.py", line 126, in _fail
        raise RuntimeError('the session is unavailable because no secret '
    RuntimeError: the session is unavailable because no secret key was set.  Set the secret_key on the application to something unique and secret.

In your case the exception is raised by the NullSessionInterface session implementation, which is the default session type when you use Flask-Session. That's because you don't ever actually give the SESSION_TYPE configuration to Flask ; it is not enough to set it as a global in your module. The Flask-Session quickstart example code does set a global, but then uses the current module as a configuration object by calling app.config.from_object(__name__).

This default doesn't make much sense with Flask 0.10 or newer; NullSession may have made sense with Flask 0.8 or 0.9, but in current version the flask.session.NullSession class is used as an error signal. In your case it gives you the wrong error message now.

Set the SESSION_TYPE configuration option to something else. Pick one of redis, memcached, filesystem or mongodb, and make sure to set it in app.config (directly or via the various Config.from_* methods).

For a quick test, setting it to filesystem is easiest; there is enough default configuration there to have that work without additional dependencies:

    if __name__ == "__main__":
        app.secret_key = 'super secret key'
        app.config['SESSION_TYPE'] = 'filesystem'

        sess.init_app(app)

        app.debug = True
        app.run()

If you see this error and you are not using Flask-Session, then something has gone wrong with setting the secret. If you are setting app.config['SECRET_KEY'] or app.secret_key in a if __name__ == "__main__": guard like above and you get this error, then you are probably running your Flask app via a WSGI server that imports your Flask project as a module , and the __name__ == "__main__" block is never run.

It is always better to manage configuration for Flask apps in a separate file, anyway.

From: stackoverflow.com/q/26080872