Use warnings instead

traits/observation/exception_handling.py

@@ -11,11 +11,9 @@
 # This module provides the push_exception_handler and pop_exception_handler
 # for the observers.
 
-import logging
+import warnings
 import sys
-
-
-_logger = logging.getLogger("traits")
+import traceback
 
 
 class ObserverExceptionHandler:
@@ -25,27 +23,31 @@ class ObserverExceptionHandler:
     ----------
     handler : callable(event) or None
         A callable to handle an event, in the context of
-        an exception. If None, the exceptions will be logged.
+        an exception. If None, the exceptions will result in a warning.
     reraise_exceptions : boolean
         Whether to reraise the exception.
     """
 
     def __init__(self, handler, reraise_exceptions):
-        self.handler = handler if handler is not None else self._log_exception
+        self.handler = handler if handler is not None else self._warn
         self.reraise_exceptions = reraise_exceptions
 
-    def _log_exception(self, event):
-        """ A handler that logs the exception with the given event.
+    def _warn(self, event):
+        """ A handler that warns about the exception with the given event.
 
         Parameters
         ----------
         event : object
             An event object emitted by the notification.
         """
-        _logger.exception(
+        _, _, tb = sys.exc_info()
+        texts = traceback.format_tb(tb)
+        warnings.warn(
             "Exception occurred in traits notification handler "
-            "for event object: %r",
-            event,
+            "for event object: {!r}\n{}".format(
+                event, "\n".join(texts)
+            ),
+            RuntimeWarning,
         )
 
 
@@ -70,7 +72,7 @@ def push_exception_handler(
         ----------
         handler : callable(event) or None
             A callable to handle an event, in the context of
-            an exception. If None, the exceptions will be logged.
+            an exception. If None, exceptions will result in warnings.
         reraise_exceptions : boolean
             Whether to reraise the exception.
         """

traits/observation/tests/test_exception_handling.py

@@ -24,17 +24,16 @@ class TestExceptionHandling(unittest.TestCase):
     def test_default_logging(self):
         stack = ObserverExceptionHandlerStack()
 
-        with self.assertLogs("traits", level="ERROR") as log_context:
+        with self.assertWarns(RuntimeWarning) as warn_context:
             try:
                 raise ZeroDivisionError()
             except Exception:
                 stack.handle_exception("Event")
 
-        content, = log_context.output
         self.assertIn(
             "Exception occurred in traits notification handler for "
             "event object: {!r}".format("Event"),
-            content,
+            str(warn_context.warning),
         )
 
     def test_push_exception_handler(self):
@@ -45,16 +44,15 @@ def test_push_exception_handler(self):
 
         stack.push_exception_handler(reraise_exceptions=True)
 
-        with self.assertLogs("traits", level="ERROR") as log_context, \
+        with self.assertWarns(RuntimeWarning) as warn_context, \
                 self.assertRaises(ZeroDivisionError):
 
             try:
                 raise ZeroDivisionError()
             except Exception:
                 stack.handle_exception("Event")
 
-        content, = log_context.output
-        self.assertIn("ZeroDivisionError", content)
+        self.assertIn("ZeroDivisionError", str(warn_context.warning))
 
     def test_push_exception_handler_collect_events(self):
 

traits/observation/tests/test_trait_event_notifier.py

@@ -169,17 +169,16 @@ def misbehaving_handler(event):
         notifier = create_notifier(handler=misbehaving_handler)
 
         # when
-        with self.assertLogs("traits", level="ERROR") as log_exception:
+        with self.assertWarns(RuntimeWarning) as warn_context:
             notifier(a=1, b=2)
 
         # then
-        content, = log_exception.output
         self.assertIn(
             "Exception occurred in traits notification handler",
-            content,
+            str(warn_context.warning),
         )
         # The tracback should be included
-        self.assertIn("ZeroDivisionError", content)
+        self.assertIn("ZeroDivisionError", str(warn_context.warning))
 
 
 class TestTraitEventNotifierEqual(unittest.TestCase):