ImportError error while importing class from auth/mixin to auth/view.

[Mehmet İnce]

While I was doing some tests about discussion related to the ​https://groups.google.com/forum/#!topic/django-developers/PUQQUHIxEXQ , I've realized that it's not possible to import class from django.contrib.auth.mixins to the django.contrib.auth.views .

Reproduce

Add following mixin to the auth/mixins.py

class LoginRequiredExemptMixin(object):
    login_required_exempt = True

And import it at auth/views.py and use it on one of the CBV. For instance LoginView.

from django.contrib.auth.mixins import LoginRequiredExemptMixin

class LoginView(SuccessURLAllowedHostsMixin, FormView, LoginRequiredExemptMixin):
    """
    Display the login form and handle the login action.
    """

In that case, you will be seeing following ImportError

  File "/Users/xxx/PycharmProjects/django/django/contrib/auth/mixins.py", line 4, in <module>
    from django.contrib.auth.views import redirect_to_login
  File "/Users/xxx/PycharmProjects/django/django/contrib/auth/views.py", line 13, in <module>
    from django.contrib.auth.mixins import LoginRequiredExemptMixin
ImportError: cannot import name 'LoginRequiredExemptMixin' from 'django.contrib.auth.mixins' (/Users/mince/PycharmProjects/django/django/contrib/auth/mixins.py)

How To Fix

The reason of the error is mixins.py file have "django.contrib.auth.views import redirect_to_login" on line 4. Since the redirect_to_login is only used one place (handle_no_permission function) in mixin.py we can remove the import from top of the file and call it right before usage of the imported function. For example as follow.

    def handle_no_permission(self):
        if self.raise_exception or self.request.user.is_authenticated:
            raise PermissionDenied(self.get_permission_denied_message())
        from django.contrib.auth.views import redirect_to_login
        return redirect_to_login(self.request.get_full_path(), self.get_login_url(), self.get_redirect_field_name())

On the other hand, I think why we have SuccessURLAllowedHostsMixin class in auth/views.py file even though it's been called Mixin was related that import code in mixin.py too.

By doing this changes we can even move SuccessURLAllowedHostsMixin class to the mixins.py file since it's only being used in auth/views.py. That little changes gives us flexibility to import mixings in the feature.

[Mehmet İnce]

​https://github.com/django/django/pull/12577/

[Mariusz Felisiak]

Thanks for this ticket, however django.contrib.auth.mixins contains ​documented mixins that can be used with CBVs. SuccessURLAllowedHostsMixin is not one of them, it's an internal mixin specific for login/logout views, so currently there is no need to import anything from django.contrib.auth.mixins in the django.contrib.auth.views.