django1/django/contrib/auth/context_processors.py

# PermWrapper and PermLookupDict proxy the permissions system into objects that
# the template system can understand.

class PermLookupDict(object):
    def __init__(self, user, module_name):
        self.user, self.module_name = user, module_name

    def __repr__(self):
        return str(self.user.get_all_permissions())

    def __getitem__(self, perm_name):
        return self.user.has_perm("%s.%s" % (self.module_name, perm_name))

    def __nonzero__(self):
        return self.user.has_module_perms(self.module_name)


class PermWrapper(object):
    def __init__(self, user):
        self.user = user

    def __getitem__(self, module_name):
        return PermLookupDict(self.user, module_name)

    def __iter__(self):
        # I am large, I contain multitudes.
        raise TypeError("PermWrapper is not iterable.")

def auth(request):
    """
    Returns context variables required by apps that use Django's authentication
    system.

    If there is no 'user' attribute in the request, uses AnonymousUser (from
    django.contrib.auth).
    """
    if hasattr(request, 'user'):
        user = request.user
    else:
        from django.contrib.auth.models import AnonymousUser
        user = AnonymousUser()

    return {
        'user': user,
        'perms': PermWrapper(user),
    }