Fix mutable default arguments in OrderingFilter methods

killerdevildog · killerdevildog · commit 0b5cbea68e47 · 2025-07-17T18:41:59.000-06:00
- Fixed get_default_valid_fields() and get_valid_fields() methods in filters.py - Changed context={} default parameter to context=None to prevent mutable default anti-pattern - Added proper None checking with context = {} assignment inside methods Why this fix is important: - Mutable default arguments (context={}) create shared state across function calls - Same dict object gets reused, potentially causing unexpected side effects - This is a well-known Python anti-pattern that can lead to bugs What was changed: - Line 249: get_default_valid_fields(self, queryset, view, context=None) - Line 285: get_valid_fields(self, queryset, view, context=None) - Added 'if context is None: context = {}' in both methods Testing results: - All existing filter tests pass (pytest tests/test_filters.py) - Custom verification script confirms fix works correctly - Maintains backward compatibility - No breaking changes to API Addresses GitHub issue #9741
diff --git a/rest_framework/filters.py b/rest_framework/filters.py
@@ -249,7 +249,9 @@ def get_default_ordering(self, view):
             return (ordering,)
         return ordering
 
-    def get_default_valid_fields(self, queryset, view, context={}):
+    def get_default_valid_fields(self, queryset, view, context=None):
+        if context is None:
+            context = {}
         # If `ordering_fields` is not specified, then we determine a default
         # based on the serializer class, if one exists on the view.
         if hasattr(view, 'get_serializer_class'):
@@ -286,7 +288,9 @@ def get_default_valid_fields(self, queryset, view, context={}):
             )
         ]
 
-    def get_valid_fields(self, queryset, view, context={}):
+    def get_valid_fields(self, queryset, view, context=None):
+        if context is None:
+            context = {}
         valid_fields = getattr(view, 'ordering_fields', self.ordering_fields)
 
         if valid_fields is None:
