Update _valid_warning_category and test for debug mode

Author: hasrat17

Lib/_py_warnings.py

@@ -255,13 +255,13 @@ def _valid_warning_category(category):
     Return True if category is a Warning subclass or tuple of such.
     Always perform class checks; only perform tuple iteration in debug mode.
     """
+    if not __debug__:
+        return True
     if isinstance(category, type) and issubclass(category, Warning):
         return True
     if isinstance(category, tuple):
-        if __debug__:
-            return all(isinstance(c, type) and issubclass(c, Warning)
-                       for c in category)
-        return True
+        return all(isinstance(c, type) and issubclass(c, Warning)
+                    for c in category)
     return False
 
 def filterwarnings(action, message="", category=Warning, module="", lineno=0,

Lib/test/test_warnings/__init__.py

@@ -398,6 +398,8 @@ def test_argument_validation(self):
         with self.assertRaises(ValueError):
             self.module.simplefilter('ignore', lineno=-1)
 
+    # these tests fail if python is run with -O, so check __debug__
+    @unittest.skipUnless(__debug__, "Won't work if __debug__ is False")
     def test_invalid_category_types(self):
         with self.assertRaises(TypeError):
             self.module.filterwarnings("ignore", category="notawarning")