Fix authtoken.TokenProxy error when not installed in Django apps

Author: terencehonles

rest_framework/authtoken/models.py

@@ -2,6 +2,7 @@
 import os
 
 from django.conf import settings
+from django.core.exceptions import ImproperlyConfigured
 from django.db import models
 from django.utils.translation import gettext_lazy as _
 
@@ -40,14 +41,22 @@ def __str__(self):
         return self.key
 
 
-class TokenProxy(Token):
-    """
-    Proxy mapping pk to user pk for use in admin.
-    """
-    @property
-    def pk(self):
-        return self.user.pk
-
-    class Meta:
-        proxy = True
-        verbose_name = "token"
+if 'rest_framework.authtoken' in settings.INSTALLED_APPS:
+    class TokenProxy(Token):
+        """
+        Proxy mapping pk to user pk for use in admin.
+        """
+        @property
+        def pk(self):
+            return self.user.pk
+
+        class Meta:
+            proxy = True
+            verbose_name = "token"
+else:
+    class TokenProxy:
+        def __init__(self, *args, **kwargs):
+            raise ImproperlyConfigured(
+                '"rest_framework.authtoken" must be in your '
+                'settings.INSTALLED_APPS to use the Token or TokenProxy '
+                'model.')