Issue #16382: Improve exception message of warnings.warn() for bad category.
Initial patch by Phil Elson.
diff --git a/Lib/test/test_warnings.py b/Lib/test/test_warnings.py
index cf7f747..cd3288b 100644
--- a/Lib/test/test_warnings.py
+++ b/Lib/test/test_warnings.py
@@ -370,6 +370,41 @@
with self.assertRaises(ValueError):
self.module.warn(BadStrWarning())
+ def test_warning_classes(self):
+ class MyWarningClass(Warning):
+ pass
+
+ class NonWarningSubclass:
+ pass
+
+ # passing a non-subclass of Warning should raise a TypeError
+ with self.assertRaises(TypeError) as cm:
+ self.module.warn('bad warning category', '')
+ self.assertIn('category must be a Warning subclass, not ',
+ str(cm.exception))
+
+ with self.assertRaises(TypeError) as cm:
+ self.module.warn('bad warning category', NonWarningSubclass)
+ self.assertIn('category must be a Warning subclass, not ',
+ str(cm.exception))
+
+ # check that warning instances also raise a TypeError
+ with self.assertRaises(TypeError) as cm:
+ self.module.warn('bad warning category', MyWarningClass())
+ self.assertIn('category must be a Warning subclass, not ',
+ str(cm.exception))
+
+ with self.assertWarns(MyWarningClass) as cm:
+ self.module.warn('good warning category', MyWarningClass)
+ self.assertEqual('good warning category', str(cm.warning))
+
+ with self.assertWarns(UserWarning) as cm:
+ self.module.warn('good warning category', None)
+ self.assertEqual('good warning category', str(cm.warning))
+
+ with self.assertWarns(MyWarningClass) as cm:
+ self.module.warn('good warning category', MyWarningClass)
+ self.assertIsInstance(cm.warning, Warning)
class CWarnTests(WarnTests, unittest.TestCase):
module = c_warnings
diff --git a/Lib/warnings.py b/Lib/warnings.py
index a427e35..f37b8a7 100644
--- a/Lib/warnings.py
+++ b/Lib/warnings.py
@@ -162,7 +162,9 @@
# Check category argument
if category is None:
category = UserWarning
- assert issubclass(category, Warning)
+ if not (isinstance(category, type) and issubclass(category, Warning)):
+ raise TypeError("category must be a Warning subclass, "
+ "not '{:s}'".format(type(category).__name__))
# Get context information
try:
caller = sys._getframe(stacklevel)