Fix viewset actions dict being mutated after first request (#9747)

rest_framework/viewsets.py

@@ -103,17 +103,18 @@ class ViewSetMixin:
         def view(request, *args, **kwargs):
             self = cls(**initkwargs)
 
-            if 'get' in actions and 'head' not in actions:
-                actions['head'] = actions['get']
+            bound_actions = dict(actions)
+            if 'get' in bound_actions and 'head' not in bound_actions:
+                bound_actions['head'] = bound_actions['get']
 
             # We also store the mapping of request methods to actions,
             # so that we can later set the action attribute.
             # eg. `self.action = 'list'` on an incoming GET request.
-            self.action_map = actions
+            self.action_map = bound_actions
 
             # Bind methods to actions
             # This is the bit that's different to a standard view
-            for method, action in actions.items():
+            for method, action in bound_actions.items():
                 handler = getattr(self, action)
                 setattr(self, method, handler)
 

tests/test_viewsets.py

@@ -190,6 +190,19 @@ class InitializeViewSetsTestCase(TestCase):
         assert get.view.action == 'list'
         assert head.view.action == 'list'
 
+    def test_actions_dict_not_mutated(self):
+        """
+        The original actions dict passed to as_view() should not be mutated.
+        Regression test for #9747.
+        """
+        actions = {'get': 'list'}
+        view = ActionViewSet.as_view(actions=actions)
+
+        assert 'head' not in actions
+        view(factory.get('/'))
+        assert 'head' not in actions
+        assert view.actions == {'get': 'list'}
+
     def test_viewset_action_attr_for_extra_action(self):
         view = ActionViewSet.as_view(actions=dict(ActionViewSet.list_action.mapping))