Added testcase and refactored warning logic for debug

Author: hasrat17

Lib/_py_warnings.py

@@ -251,10 +251,18 @@ def _formatwarnmsg(msg):
     return _wm._formatwarnmsg_impl(msg)
 
 def _valid_warning_category(category):
-    """Return True if category is a Warning subclass or tuple of such."""
+    """
+    Return True if category is a Warning subclass or tuple of such.
+    Always perform class checks; only perform tuple iteration in debug mode.
+    """
+    if isinstance(category, type) and issubclass(category, Warning):
+        return True
     if isinstance(category, tuple):
-        return all(isinstance(c, type) and issubclass(c, Warning) for c in category)
-    return isinstance(category, type) and issubclass(category, Warning)
+        if __debug__:
+            return all(isinstance(c, type) and issubclass(c, Warning)
+                       for c in category)
+        return True
+    return False
 
 def filterwarnings(action, message="", category=Warning, module="", lineno=0,
                    append=False):

Lib/test/test_warnings/__init__.py

@@ -398,6 +398,33 @@ def test_argument_validation(self):
         with self.assertRaises(ValueError):
             self.module.simplefilter('ignore', lineno=-1)
 
+    def test_invalid_category_types(self):
+        with self.assertRaises(TypeError):
+            self.module.filterwarnings("ignore", category="notawarning")
+        with self.assertRaises(TypeError):
+            self.module.filterwarnings("ignore", category=123)
+        with self.assertRaises(TypeError):
+            self.module.filterwarnings("ignore", category=17.02)
+        with self.assertRaises(TypeError):
+            self.module.filterwarnings("ignore", category=True)
+        with self.assertRaises(TypeError):
+            self.module.filterwarnings(
+                "ignore", category=(UserWarning, 17)
+            )
+
+        with self.assertRaises(TypeError):
+            self.module.simplefilter("ignore", category="notawarning")
+        with self.assertRaises(TypeError):
+            self.module.simplefilter("ignore", category=123)
+        with self.assertRaises(TypeError):
+            self.module.filterwarnings("ignore", category=17.02)
+        with self.assertRaises(TypeError):
+            self.module.filterwarnings("ignore", category=True)
+        with self.assertRaises(TypeError):
+            self.module.simplefilter(
+                "ignore", category=(UserWarning, 'abc')
+            )
+
     def test_catchwarnings_with_simplefilter_ignore(self):
         with self.module.catch_warnings(module=self.module):
             self.module.resetwarnings()

Misc/ACKS

@@ -74,6 +74,7 @@ Emmanuel Arias
 Alicia Arlen
 Jeffrey Armstrong
 Justin Turner Arthur
+Hasrat Ali Arzoo
 Jason Asbahr
 David Ascher
 Ammar Askar
@@ -2149,6 +2150,5 @@ Jelle Zijlstra
 Gennadiy Zlobin
 Doug Zongker
 Peter Åstrand
-Hasrat Ali Arzoo
 
 (Entries should be added in rough alphabetical order by last names)

Misc/NEWS.d/next/Windows/2025-07-10-19-28-11.gh-issue-125893.lD8Nyd.rst

@@ -0,0 +1,2 @@
+Added validation for the ``category`` argument in
+``warnings.filterwarnings()`` and ``warnings.simplefilter()``