diff --git a/openslides/agenda/apps.py b/openslides/agenda/apps.py
index 88baf1fb8..00d358838 100644
--- a/openslides/agenda/apps.py
+++ b/openslides/agenda/apps.py
@@ -9,9 +9,12 @@ class AgendaAppConfig(AppConfig):
 
     def ready(self):
         # Import all required stuff.
-        from django.db.models.signals import pre_delete, post_save
+        from django.db.models.signals import post_save, pre_delete
+
         from ..core.signals import permission_change
+        from ..utils.access_permissions import required_user
         from ..utils.rest_api import router
+        from . import serializers  # noqa
         from .projector import register_projector_slides
         from .signals import (
             get_permission_change_data,
@@ -19,8 +22,6 @@ class AgendaAppConfig(AppConfig):
             listen_to_related_object_post_save,
         )
         from .views import ItemViewSet, ListOfSpeakersViewSet
-        from . import serializers  # noqa
-        from ..utils.access_permissions import required_user
 
         # Define projector elements.
         register_projector_slides()
diff --git a/openslides/assignments/apps.py b/openslides/assignments/apps.py
index fb65e081e..2397ca945 100644
--- a/openslides/assignments/apps.py
+++ b/openslides/assignments/apps.py
@@ -16,9 +16,9 @@ class AssignmentsAppConfig(AppConfig):
         from .projector import register_projector_slides
         from .signals import get_permission_change_data
         from .views import (
-            AssignmentViewSet,
-            AssignmentPollViewSet,
             AssignmentOptionViewSet,
+            AssignmentPollViewSet,
+            AssignmentViewSet,
             AssignmentVoteViewSet,
         )
 
@@ -82,7 +82,7 @@ async def required_users_assignments(element: Dict[str, Any]) -> Set[int]:
     Returns all user ids that are displayed as candidates (including poll
     options) in the assignment element.
     """
-    from openslides.assignments.models import AssignmentPoll, AssignmentOption
+    from openslides.assignments.models import AssignmentOption, AssignmentPoll
     from openslides.utils.cache import element_cache
 
     candidates = set(
diff --git a/openslides/core/apps.py b/openslides/core/apps.py
index 3481e402a..1899e24dc 100644
--- a/openslides/core/apps.py
+++ b/openslides/core/apps.py
@@ -15,9 +15,12 @@ class CoreAppConfig(AppConfig):
 
     def ready(self):
         # Import all required stuff.
+        # Let all client websocket message register
+        from ..utils import websocket_client_messages  # noqa
+        from ..utils.rest_api import router
+        from . import serializers  # noqa
         from .config import config
         from .projector import register_projector_slides
-        from . import serializers  # noqa
         from .signals import (
             autoupdate_for_many_to_many_relations,
             cleanup_unused_permissions,
@@ -29,15 +32,11 @@ class CoreAppConfig(AppConfig):
         from .views import (
             ConfigViewSet,
             CountdownViewSet,
+            ProjectionDefaultViewSet,
             ProjectorMessageViewSet,
             ProjectorViewSet,
-            ProjectionDefaultViewSet,
             TagViewSet,
         )
-        from ..utils.rest_api import router
-
-        # Let all client websocket message register
-        from ..utils import websocket_client_messages  # noqa
 
         # Collect all config variables before getting the constants.
         config.collect_config_variables_from_apps()
@@ -92,9 +91,9 @@ class CoreAppConfig(AppConfig):
             run_startup_hooks()
 
     def get_startup_hooks(self):
-        from openslides.utils.constants import set_constants_from_apps
-        from openslides.utils.cache import element_cache
         from openslides.core.models import History
+        from openslides.utils.cache import element_cache
+        from openslides.utils.constants import set_constants_from_apps
 
         return {
             10: element_cache.ensure_schema_version,
diff --git a/openslides/mediafiles/apps.py b/openslides/mediafiles/apps.py
index 0dcf06fdc..ce557ae42 100644
--- a/openslides/mediafiles/apps.py
+++ b/openslides/mediafiles/apps.py
@@ -11,10 +11,11 @@ class MediafilesAppConfig(AppConfig):
         # Import all required stuff.
         from openslides.core.signals import permission_change
         from openslides.utils.rest_api import router
+
+        from . import serializers  # noqa
         from .projector import register_projector_slides
         from .signals import get_permission_change_data
         from .views import MediafileViewSet
-        from . import serializers  # noqa
 
         # Validate, that the media_url is correct formatted:
         # Must begin and end with a slash. It has to be at least "/".
diff --git a/openslides/motions/apps.py b/openslides/motions/apps.py
index 087aedb0d..7a0d0c90b 100644
--- a/openslides/motions/apps.py
+++ b/openslides/motions/apps.py
@@ -12,23 +12,24 @@ class MotionsAppConfig(AppConfig):
         # Import all required stuff.
         from openslides.core.signals import permission_change
         from openslides.utils.rest_api import router
+
+        from ..utils.access_permissions import required_user
+        from . import serializers  # noqa
         from .projector import register_projector_slides
         from .signals import create_builtin_workflows, get_permission_change_data
-        from . import serializers  # noqa
         from .views import (
             CategoryViewSet,
-            StatuteParagraphViewSet,
-            MotionViewSet,
-            MotionCommentSectionViewSet,
-            MotionVoteViewSet,
             MotionBlockViewSet,
-            MotionPollViewSet,
-            MotionOptionViewSet,
             MotionChangeRecommendationViewSet,
+            MotionCommentSectionViewSet,
+            MotionOptionViewSet,
+            MotionPollViewSet,
+            MotionViewSet,
+            MotionVoteViewSet,
             StateViewSet,
+            StatuteParagraphViewSet,
             WorkflowViewSet,
         )
-        from ..utils.access_permissions import required_user
 
         # Define projector elements.
         register_projector_slides()
diff --git a/openslides/topics/apps.py b/openslides/topics/apps.py
index 10f0d6790..0424f8562 100644
--- a/openslides/topics/apps.py
+++ b/openslides/topics/apps.py
@@ -8,11 +8,12 @@ class TopicsAppConfig(AppConfig):
     def ready(self):
         # Import all required stuff.
         from openslides.core.signals import permission_change
+
         from ..utils.rest_api import router
+        from . import serializers  # noqa
         from .projector import register_projector_slides
         from .signals import get_permission_change_data
         from .views import TopicViewSet
-        from . import serializers  # noqa
 
         # Define projector elements.
         register_projector_slides()
diff --git a/openslides/users/access_permissions.py b/openslides/users/access_permissions.py
index 6bc1f92ae..4e4084f01 100644
--- a/openslides/users/access_permissions.py
+++ b/openslides/users/access_permissions.py
@@ -19,8 +19,8 @@ class UserAccessPermissions(BaseAccessPermissions):
         not get the fields they should not get.
         """
         from .serializers import (
-            USERCANSEESERIALIZER_FIELDS,
             USERCANSEEEXTRASERIALIZER_FIELDS,
+            USERCANSEESERIALIZER_FIELDS,
         )
 
         def filtered_data(full_data, whitelist, whitelist_operator=None):
diff --git a/openslides/users/apps.py b/openslides/users/apps.py
index 200578d72..71e18d7cd 100644
--- a/openslides/users/apps.py
+++ b/openslides/users/apps.py
@@ -12,9 +12,9 @@ class UsersAppConfig(AppConfig):
 
     def ready(self):
         # Import all required stuff.
-        from . import serializers  # noqa
-        from ..core.signals import post_permission_creation, permission_change
+        from ..core.signals import permission_change, post_permission_creation
         from ..utils.rest_api import router
+        from . import serializers  # noqa
         from .projector import register_projector_slides
         from .signals import create_builtin_groups_and_admin, get_permission_change_data
         from .views import GroupViewSet, PersonalNoteViewSet, UserViewSet
diff --git a/openslides/utils/cache_providers.py b/openslides/utils/cache_providers.py
index d37d2e058..53676d011 100644
--- a/openslides/utils/cache_providers.py
+++ b/openslides/utils/cache_providers.py
@@ -20,7 +20,7 @@ from .utils import split_element_id, str_dict_to_bytes
 logger = logging.getLogger(__name__)
 
 if use_redis:
-    from .redis import get_connection, aioredis
+    from .redis import aioredis, get_connection
 
 
 class CacheReset(Exception):
diff --git a/requirements/development.txt b/requirements/development.txt
index 4bcc167eb..c419bae22 100644
--- a/requirements/development.txt
+++ b/requirements/development.txt
@@ -1,7 +1,7 @@
 black
 coverage
 flake8
-isort
+isort<5.0.0
 mypy
 pytest<5.4.2
 pytest-django<3.9.0
diff --git a/tests/conftest.py b/tests/conftest.py
index 01885741b..514d9401e 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -64,7 +64,7 @@ def constants(request, reset_cache):
 
     Uses fake constants, if the db is not in use.
     """
-    from openslides.utils.constants import set_constants, get_constants_from_apps
+    from openslides.utils.constants import get_constants_from_apps, set_constants
 
     if "django_db" in request.node.keywords or is_django_unittest(request):
         # When the db is created, use the original constants
diff --git a/tests/settings.py b/tests/settings.py
index 37f1e2ac6..912e7eb96 100644
--- a/tests/settings.py
+++ b/tests/settings.py
@@ -1,7 +1,6 @@
 """
 Settings file for OpenSlides' tests.
 """
-
 import os
 
 from openslides.global_settings import *  # noqa
@@ -82,7 +81,8 @@ ENABLE_ELECTRONIC_VOTING = True
 # https://stackoverflow.com/questions/24876343/django-traceback-on-queries
 if os.environ.get("DEBUG_SQL_TRACEBACK"):
     import traceback
-    import django.db.backends.utils as bakutils
+
+    from django.db.backends import utils as bakutils
 
     cursor_debug_wrapper_orig = bakutils.CursorDebugWrapper