Flask-Login "load_user() missing 1 required positional argument: 'user_id'"

Question

I am currently using Flask-Login for authentication, however I am getting an error that load_user() missing 1 required positional argument: 'user_id' but when I debug my app, user_id exists and is being correctly passed into the login_user() function (and stored in the session['user_id'] variable).

Below is my code for logging a user in and then navigating to home page:

@app.route('/', methods=['GET', 'POST'])
def login():
    login_form = LoginForm()
    username = login_form.username.data
    password = login_form.password.data
    if user_details_valid(username, password):
        login_user(user_service.get_user_object(username))
        return redirect(url_for(‘home’))
    return render_template('login.html', form=login_form)

@app.route(‘/home’)
@login_required
def home():
    return render_template(“home.html")

The User model is as follows:

class User(UserMixin):

def __init__(self, username):
    self.username = username
    self.email = None
    self.password = None
    self.user_id = None

def is_authenticated(self):
    return True

def is_active(self):
    return True

def is_anonymous(self):
    return False

def get_id(self):
    return str(self.user_id)

def set_id(self, user_id):
    self.user_id = user_id

def set_password(self, password_hash):
    self.password = password_hash

def set_email(self, email):
    self.email = email

The stacktrace I am getting is:

File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/flask/app.py", line 1836, in __call__
    return self.wsgi_app(environ, start_response)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/flask/app.py", line 1820, in wsgi_app
    response = self.make_response(self.handle_exception(e))
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/flask/app.py", line 1403, in handle_exception
    reraise(exc_type, exc_value, tb)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/flask/_compat.py", line 33, in reraise
    raise value
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/flask/app.py", line 1817, in wsgi_app
    response = self.full_dispatch_request()
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/flask/app.py", line 1477, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/flask/app.py", line 1381, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/flask/_compat.py", line 33, in reraise
    raise value
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/flask/app.py", line 1475, in full_dispatch_request
    rv = self.dispatch_request()
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/flask/app.py", line 1461, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/flask_login.py", line 756, in decorated_view
    elif not current_user.is_authenticated():
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/werkzeug/local.py", line 347, in __getattr__
    return getattr(self._get_current_object(), name)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/werkzeug/local.py", line 306, in _get_current_object
    return self.__local()
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/flask_login.py", line 46, in <lambda>
    current_user = LocalProxy(lambda: _get_user())
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/flask_login.py", line 794, in _get_user
    current_app.login_manager._load_user()
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/flask_login.py", line 363, in _load_user
    return self.reload_user()
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/flask_login.py", line 325, in reload_user
    user = self.user_callback(user_id)
TypeError: load_user() missing 1 required positional argument: 'user_id'

My user_loader is in the user_service class and is as follows:

@login.user_loader
def load_user(self, user_id):
    return self.collection.find_one({"user_id": user_id})

Updated my post to include it. I think it is working correctly as when debugging the session.get('user_id') returns the user_id correctly, it only seems to be when loading the home page with the @login_required decorator the error occurs — Brian Hamill
– Brian Hamill, Commented Mar 5, 2018 at 11:51

d5avard · Accepted Answer · 2020-04-19 20:14:35Z

2

I got the same error. When I initialize the LoginManager I forgot to pass the instance of the app as an argument.

app/init.py

#...
from flask_login import LoginManager
app = Flask(__name__)
# ...
login = LoginManager(app)

answered Apr 19, 2020 at 20:14

d5avard

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Comments

Brian Hamill · Accepted Answer · 2018-03-13 12:31:50Z

0

To resolve this error I placed my user_loader inside my __init__.py file, as demonstrated in this youtube tutorial.

This is, however, not a perfect answer as neither Miguel's guide, the RealPython guide nor RunningCodes flask-login pymongo guide show this as the case, in fact both Miguel's guide and RunningCode's guide specifically have the user_loader in different parts of the app.

This solution does not make sense, as I have to access my database from inside my __init__.py which seems extremely messy but I was able to fix the error and properly login.

The error may be occurring because my __init__.py seems to be loading twice, I found another answer somewhere on SO that stated similar errors due to two instances of the app running.

edited Mar 13, 2018 at 12:31

answered Mar 6, 2018 at 18:55

Brian Hamill

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