You should probably set DEBUG at False. This is very undesirable in a production environment as it will probably leak sensitive information that attackers can use against your site. Unless, of course, if you use only the Django ORM.
For the case when the user isn't willing to give access to his/her twitter account.
The error returned is KeyError, since you are trying to access :
user = User.objects.get(username = authorized_tokens['screen_name'])
I see that you have put a try, except blocks. But you are not catching the KeyError exception. You are only making an exception when the user doesn't exist.
you should add a block : except KeyError. And figure out the logic for this particular case. (probably just redirecting the user to the home page)