From d1dc3a98c612d24f951dcc004283517d8f92e322 Mon Sep 17 00:00:00 2001
From: SeaStar Deng <37767638+DSeaStar@users.noreply.github.com>
Date: Fri, 14 Aug 2026 20:53:39 +0000
Subject: [PATCH 1/2] Warn on unrecognized Configurable kwargs with UserWarning

HasTraits already warned when leftover kwargs reached object.__init__,
but it used DeprecationWarning at stacklevel=2. That points at
Configurable.__init__, so IPython hid the message. UserWarning is
visible by default, which matches the discussion on #926.
---
 tests/test_traitlets.py | 17 +++++++++++++++++
 traitlets/traitlets.py  |  2 +-
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/tests/test_traitlets.py b/tests/test_traitlets.py
index 2e7b8459..fabcd30d 100644
--- a/tests/test_traitlets.py
+++ b/tests/test_traitlets.py
@@ -2829,6 +2829,23 @@ class SuperHasTraits(HasTraits):
     assert not hasattr(obj, "b")
 
 
+def test_configurable_unrecognized_args_user_warning():
+    """Configurable should surface unknown kwargs as UserWarning (#926)."""
+    import warnings
+
+    from traitlets.config.configurable import Configurable
+
+    with warnings.catch_warnings(record=True) as caught:
+        warnings.simplefilter("always")
+        Configurable(not_a_trait=1)
+    user = [w for w in caught if issubclass(w.category, UserWarning)]
+    assert user
+    assert "Passing unrecognized arguments" in str(user[0].message)
+    assert not any(issubclass(w.category, DeprecationWarning) and
+                   "Passing unrecognized arguments" in str(w.message)
+                   for w in caught)
+
+
 def test_default_mro():
     """Verify that default values follow mro"""
 
diff --git a/traitlets/traitlets.py b/traitlets/traitlets.py
index 0989ea98..146f2e74 100644
--- a/traitlets/traitlets.py
+++ b/traitlets/traitlets.py
@@ -1399,7 +1399,7 @@ def ignore(change: Bunch) -> None:
                 f"{e}\n"
                 "This is deprecated in traitlets 4.2."
                 "This error will be raised in a future release of traitlets.",
-                DeprecationWarning,
+                UserWarning,
                 stacklevel=2,
             )
 

From 3d606be2a43f4f14c2405c88956fc786bd1c8cc4 Mon Sep 17 00:00:00 2001
From: "pre-commit-ci[bot]"
 <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Date: Fri, 14 Aug 2026 20:54:07 +0000
Subject: [PATCH 2/2] style: pre-commit fixes

---
 tests/test_traitlets.py | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/tests/test_traitlets.py b/tests/test_traitlets.py
index fabcd30d..6cfa3051 100644
--- a/tests/test_traitlets.py
+++ b/tests/test_traitlets.py
@@ -2841,9 +2841,11 @@ def test_configurable_unrecognized_args_user_warning():
     user = [w for w in caught if issubclass(w.category, UserWarning)]
     assert user
     assert "Passing unrecognized arguments" in str(user[0].message)
-    assert not any(issubclass(w.category, DeprecationWarning) and
-                   "Passing unrecognized arguments" in str(w.message)
-                   for w in caught)
+    assert not any(
+        issubclass(w.category, DeprecationWarning)
+        and "Passing unrecognized arguments" in str(w.message)
+        for w in caught
+    )
 
 
 def test_default_mro():