Use sessions in django in order to check if someone is loged in or not

i tried to create a dictionary key in the request.session, i called key, so it looks like that: request.session['key']=1232354 , so when a user navigate into the website i check if they have the key or not in order to know if they are logged in, the question is I'm new to Django and i am afraid that there is some big cons in these idea that i cant see,like easily getting the web site hacked or something, if there is an expert out there please tell me what do you think about this one.