middleware.py

from django.core.exceptions import ObjectDoesNotExist

class InfoMiddleware(object):
    '''
    Record refer and user-agent info about this dude.
    
    '''
    def process_request(self, request):
        if request.user.is_anonymous():
            if 'referer' not in request.session:
                request.session['referer'] = request.META.get('HTTP_REFERER')
        elif 'user_agent' not in request.session:
            user_agent = request.META.get('HTTP_USER_AGENT')
            try:
                profile = request.user.get_profile()
            except ObjectDoesNotExist:
                pass
            else:
                if profile.settings.get('user_agent') != user_agent:
                    profile.settings['user_agent'] = user_agent
                    profile.save()