gh-130907: Error when accessing __annotations__ on a partially defined module

Author: JelleZijlstra

Lib/test/test_type_annotations.py

@@ -1,9 +1,11 @@
 import annotationlib
 import inspect
+import tempfile
 import textwrap
 import types
 import unittest
-from test.support import run_code, check_syntax_error
+from pathlib import Path
+from test.support import run_code, check_syntax_error, import_helper
 
 
 class TypeAnnotationTests(unittest.TestCase):
@@ -109,6 +111,18 @@ class D(metaclass=C):
             del D.__annotations__
         self.assertEqual(D.__annotations__, {})
 
+    def test_partially_executed_module(self):
+        partialexe = import_helper.import_module("test.typinganndata.partialexecution")
+        self.assertEqual(
+            partialexe.a.__annotations__,
+            {"v1": int, "v2": int},
+        )
+        self.assertIsInstance(partialexe.b.exc, RuntimeError)
+        self.assertEqual(
+            str(partialexe.b.exc),
+            "cannot access __annotations__ while module is initializing",
+        )
+
 
 def build_module(code: str, name: str = "top") -> types.ModuleType:
     ns = run_code(code)

Misc/NEWS.d/next/Core_and_Builtins/2025-03-21-08-47-36.gh-issue-130907.rGg-ge.rst

@@ -0,0 +1,2 @@
+Raise an error if the ``__annotations__`` attribute is accessed on a module
+that has not finished executing.

Objects/moduleobject.c

@@ -1247,6 +1247,28 @@ module_get_annotations(PyObject *self, void *Py_UNUSED(ignored))
 
     PyObject *annotations;
     if (PyDict_GetItemRef(dict, &_Py_ID(__annotations__), &annotations) == 0) {
+        PyObject *spec;
+        if (PyDict_GetItemRef(m->md_dict, &_Py_ID(__spec__), &spec) < 0) {
+            Py_DECREF(dict);
+            return NULL;
+        }
+        if (spec != NULL) {
+            int rc = _PyModuleSpec_IsInitializing(spec);
+            if (rc < 0) {
+                Py_DECREF(spec);
+                Py_DECREF(dict);
+                return NULL;
+            }
+            Py_DECREF(spec);
+            if (rc) {
+                PyErr_SetString(PyExc_RuntimeError,
+                                "cannot access __annotations__ "
+                                "while module is initializing");
+                Py_DECREF(dict);
+                return NULL;
+            }
+        }
+
         PyObject *annotate;
         int annotate_result = PyDict_GetItemRef(dict, &_Py_ID(__annotate__), &annotate);
         if (annotate_result < 0) {