Use import_string for token_backend (Fixes #434) (#435)

* Use import_string for token_backend (Fixes #434)

* Fix syntax error

* Update CHANGELOG.md

* Run CI only on main branch or PR

.github/workflows/test.yml

@@ -1,6 +1,10 @@
 name: Test
 
-on: [push, pull_request]
+on:
+  push:
+    branches:
+      - main
+  pull_request:
 
 jobs:
   build:

CHANGELOG.md

@@ -1,5 +1,12 @@
 ## Unreleased
 
+## Version 4.7.3
+
+* Add integration instructions for drf-yasg ([#145](https://github.com/jazzband/djangorestframework-simplejwt/pull/145))
+* Verify Serializer Should Honour Blacklist ([#239](https://github.com/jazzband/djangorestframework-simplejwt/pull/239))
+* Added missing import in getting_started docs ([#431](https://github.com/jazzband/djangorestframework-simplejwt/pull/431))
+* Use import_string for token_backend ([#435](https://github.com/jazzband/djangorestframework-simplejwt/pull/435))
+
 ## Version 4.7.2
 
 * Fix BrowsableAPIRenderer needing `media_type` ([#426](https://github.com/jazzband/django-rest-framework-simplejwt/pull/426))

rest_framework_simplejwt/tokens.py

@@ -3,6 +3,7 @@
 
 from django.conf import settings
 from django.utils.translation import gettext_lazy as _
+from django.utils.module_loading import import_string
 
 from .exceptions import TokenBackendError, TokenError
 from .settings import api_settings
@@ -164,10 +165,15 @@ def for_user(cls, user):
         token[api_settings.USER_ID_CLAIM] = user_id
 
         return token
-
+
+    _token_backend = None
+
     def get_token_backend(self):
-        from .state import token_backend
-        return token_backend
+        if self._token_backend is None:
+            self._token_backend = import_string(
+                "rest_framework_simplejwt.state.token_backend"
+            )
+        return self._token_backend
 
 
 class BlacklistMixin: