From 4fd60dbb788f520b0609fd9f7e0df92f760e7ad9 Mon Sep 17 00:00:00 2001
From: Libba Lawrence <llawrence@microsoft.com>
Date: Fri, 10 Jul 2026 10:10:46 -0700
Subject: [PATCH] fix(http-client-python): honor models-mode=none passed to
 OptionsDict constructor

Route constructor-supplied options through _validate_and_transform so
models-mode=none normalizes to falsy False, matching __setitem__. Fixes
crash where MsrestModelSerializer entered the model-writing path.

Fixes #11046

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
---
 ...-mode-none-constructor-2026-7-10-9-46-0.md |  7 +++++
 .../generator/pygen/__init__.py               |  5 +++-
 .../tests/unit/test_options_dict.py           | 27 +++++++++++++++++++
 3 files changed, 38 insertions(+), 1 deletion(-)
 create mode 100644 .chronus/changes/fix-models-mode-none-constructor-2026-7-10-9-46-0.md
 create mode 100644 packages/http-client-python/tests/unit/test_options_dict.py

diff --git a/.chronus/changes/fix-models-mode-none-constructor-2026-7-10-9-46-0.md b/.chronus/changes/fix-models-mode-none-constructor-2026-7-10-9-46-0.md
new file mode 100644
index 00000000000..099a85bb66d
--- /dev/null
+++ b/.chronus/changes/fix-models-mode-none-constructor-2026-7-10-9-46-0.md
@@ -0,0 +1,7 @@
+---
+changeKind: fix
+packages:
+  - "@typespec/http-client-python"
+---
+
+Fix crash when generating with `models-mode=none`. Options passed to the `OptionsDict` constructor are now normalized through the same validation/transform path as `__setitem__`, so `models-mode=none` is correctly treated as falsy and a modelless client is produced instead of crashing.
diff --git a/packages/http-client-python/generator/pygen/__init__.py b/packages/http-client-python/generator/pygen/__init__.py
index b8841e4fc1a..d09e368dd18 100644
--- a/packages/http-client-python/generator/pygen/__init__.py
+++ b/packages/http-client-python/generator/pygen/__init__.py
@@ -44,7 +44,10 @@ class OptionsDict(MutableMapping):
     }
 
     def __init__(self, options: Optional[dict[str, Any]] = None) -> None:
-        self._data = options.copy() if options else {}
+        self._data = {}
+        if options:
+            for key, value in options.items():
+                self._data[key] = self._validate_and_transform(key, value)
         self._validate_combinations()
 
     def __getitem__(self, key: str) -> Any:  # pylint: disable=too-many-return-statements
diff --git a/packages/http-client-python/tests/unit/test_options_dict.py b/packages/http-client-python/tests/unit/test_options_dict.py
new file mode 100644
index 00000000000..1fa11d3bd90
--- /dev/null
+++ b/packages/http-client-python/tests/unit/test_options_dict.py
@@ -0,0 +1,27 @@
+# -------------------------------------------------------------------------
+# Copyright (c) Microsoft Corporation. All rights reserved.
+# Licensed under the MIT License. See License.txt in the project root for
+# license information.
+# --------------------------------------------------------------------------
+
+from pygen import OptionsDict
+
+
+def test_models_mode_none_normalized_via_constructor():
+    # models-mode=none must be normalized to falsy False, even when passed
+    # through the constructor (not just __setitem__).
+    assert OptionsDict({"models-mode": "none"})["models-mode"] is False
+
+
+def test_models_mode_none_normalized_via_setitem():
+    options = OptionsDict()
+    options["models-mode"] = "none"
+    assert options["models-mode"] is False
+
+
+def test_constructor_and_setitem_agree():
+    via_ctor = OptionsDict({"models-mode": "none"})["models-mode"]
+    options = OptionsDict()
+    options["models-mode"] = "none"
+    via_setitem = options["models-mode"]
+    assert via_ctor == via_setitem