Limit the growth of encodings.search_function cache

Author: StanFromIreland

Lib/encodings/__init__.py

@@ -34,6 +34,7 @@
 from . import aliases
 
 _cache = {}
+_MAXCACHE = 500
 _unknown = '--unknown--'
 _import_tail = ['*']
 _aliases = aliases.aliases
@@ -110,8 +111,8 @@ def search_function(encoding):
         mod = None
 
     if mod is None:
-        # Cache misses
-        _cache[encoding] = None
+        if len(_cache) < _MAXCACHE:
+            _cache[encoding] = None
         return None
 
     # Now ask the module for the registry entry

Lib/test/test_codecs.py

@@ -3908,5 +3908,16 @@ def test_encodings_normalize_encoding(self):
             self.assertEqual(normalize('utf\xE9\u20AC\U0010ffff-8'), 'utf_8')
 
 
+class CodecCacheTest(unittest.TestCase):
+    def test_cache_bounded(self):
+        for i in range(encodings._MAXCACHE + 1000):
+            try:
+                b'x'.decode(f'nonexist_{i}')
+            except LookupError:
+                pass
+
+        self.assertLessEqual(len(encodings._cache), encodings._MAXCACHE)
+
+
 if __name__ == "__main__":
     unittest.main()

Misc/NEWS.d/next/Library/2026-03-17-11-46-20.gh-issue-146054.udYcqn.rst

@@ -0,0 +1 @@
+Limit the size of :func:`encodings.search_function` cache.