Refactor CBV schema method limitation for set operations

rest_framework/schemas.py

@@ -246,10 +246,9 @@ class EndpointInspector(object):
         Return a list of the valid HTTP methods for this endpoint.
         """
         if hasattr(callback, 'actions'):
-            return [
-                method.upper() for method in
-                set(callback.actions.keys()).intersection(set(callback.cls().http_method_names))
-            ]
+            actions = set(callback.actions.keys())
+            http_method_names = set(callback.cls().http_method_names)
+            return [method.upper() for method in actions & http_method_names]
 
         return [
             method for method in