How to check if a user is logged in (how to properly use user.is_authenticated)?

Update for Django 1.10+:

is_authenticated is now an attribute in Django 1.10.

The method was removed in Django 2.0.

For Django 1.9 and older:

is_authenticated is a function. You should call it like

if request.user.is_authenticated():
    # do something if the user is authenticated

As Peter Rowell pointed out, what may be tripping you up is that in the default Django template language, you don't tack on parenthesis to call functions. So you may have seen something like this in template code:

{% if user.is_authenticated %}

However, in Python code, it is indeed a method in the User class.

Django 1.10+

Use an attribute, not a method:

if request.user.is_authenticated: # <-  no parentheses any more!
    # do something if the user is authenticated

The use of the method of the same name is deprecated in Django 2.0, and is no longer mentioned in the Django documentation.

return HttpResponse(json.dumps({
    "is_authenticated": request.user.is_authenticated()
}), content_type='application/json') 

that after updated to the property request.user.is_authenticated was throwing the exception TypeError: Object of type 'CallableBool' is not JSON serializable. The solution was to use JsonResponse, which could handle the CallableBool object properly when serializing:

return JsonResponse({
    "is_authenticated": request.user.is_authenticated
})