Issue #12467: warnings: fix a race condition if a warning is emitted at

shutdown, if globals()['__file__'] is None.

Lib/test/test_warnings.py

@@ -542,6 +542,18 @@ class _WarningsTests(BaseTest):
         assert expected_line
         self.assertEqual(second_line, expected_line)
 
+    def test_filename_none(self):
+        # issue #12467: race condition if a warning is emitted at shutdown
+        globals_dict = globals()
+        oldfile = globals_dict['__file__']
+        try:
+            with original_warnings.catch_warnings(module=self.module) as w:
+                self.module.filterwarnings("always", category=UserWarning)
+                globals_dict['__file__'] = None
+                original_warnings.warn('test', UserWarning)
+        finally:
+            globals_dict['__file__'] = oldfile
+
 
 class WarningsDisplayTests(unittest.TestCase):
 

Misc/NEWS

@@ -13,6 +13,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #12467: warnings: fix a race condition if a warning is emitted at
+  shutdown, if globals()['__file__'] is None.
+
 
 What's New in Python 3.2.1 release candidate 2?
 ===============================================

Python/_warnings.c

@@ -496,7 +496,7 @@ setup_context(Py_ssize_t stack_level, PyObject **filename, int *lineno,
 
     /* Setup filename. */
     *filename = PyDict_GetItemString(globals, "__file__");
-    if (*filename != NULL) {
+    if (*filename != NULL && PyUnicode_Check(*filename)) {
         Py_ssize_t len = PyUnicode_GetSize(*filename);
         Py_UNICODE *unicode = PyUnicode_AS_UNICODE(*filename);