gh-149171: Make TypeAliasType __module__ writable

ericmarkmartin · ericmarkmartin · commit ddb11affd3c6 · 2026-04-30T01:38:40.000-04:00
closes #149171.
diff --git a/Lib/test/test_type_aliases.py b/Lib/test/test_type_aliases.py
@@ -372,6 +372,8 @@ def test_module(self):
                          mod_generics_cache.__name__)
         self.assertEqual(mod_generics_cache.OldStyle.__module__,
                          mod_generics_cache.__name__)
+        Alias.__module__ = "ham.spam.eggs"
+        self.assertEqual(Alias.__module__, "ham.spam.eggs")
 
     def test_unpack(self):
         type Alias = tuple[int, int]
diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2026-04-30-01-35-09.gh-issue-149171.meXWpl.rst b/Misc/NEWS.d/next/Core_and_Builtins/2026-04-30-01-35-09.gh-issue-149171.meXWpl.rst
@@ -0,0 +1,2 @@
+Allow assignment to the ``__module__`` attribute of
+:class:`typing.TypeAliasType` instances.
diff --git a/Objects/typevarobject.c b/Objects/typevarobject.c
@@ -1998,12 +1998,22 @@ typealias_module(PyObject *self, void *Py_UNUSED(closure))
     Py_RETURN_NONE;
 }
 
+static int
+typealias_set_module(PyObject *self, PyObject *value, void *Py_UNUSED(closure))
+{
+    typealiasobject *ta = typealiasobject_CAST(self);
+    PyObject *old_module = ta->module;
+    Py_XDECREF(old_module);
+    ta->module = Py_XNewRef(value);
+    return 0;
+}
+
 static PyGetSetDef typealias_getset[] = {
     {"__parameters__", typealias_parameters, NULL, NULL, NULL},
     {"__type_params__", typealias_type_params, NULL, NULL, NULL},
     {"__value__", typealias_value, NULL, NULL, NULL},
     {"evaluate_value", typealias_evaluate_value, NULL, NULL, NULL},
-    {"__module__", typealias_module, NULL, NULL, NULL},
+    {"__module__", typealias_module, typealias_set_module, NULL, NULL},
     {0}
 };
 

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,2 @@`
	`1`	+Allow assignment to the ``__module__`` attribute of
	`2`	+:class:`typing.TypeAliasType` instances.