title: Check if Session Key is set
body: <p>I am attempting to create a relatively simple shopping cart in Django. I am storing the cart in <code>request.session['cart']</code>. Therefore, I'll need to access the data in this session when anything is added to it. However, if the session is not already set, I cannot access it without receiving an error. Is there any way to check if a session is set, so that it can be set if it doesn't exist?</p>