[3.13] gh-131670: Fix crash in `anext()` when `__anext__` is sync and raises (GH...

gh-131670: Fix crash in `anext()` when `__anext__` is sync and raises (GH-131682)
(cherry picked from commit 929afd1d6ee4fb89ac818037effe6577947103de)

Co-authored-by: sobolevn <mail@sobolevn.me>
Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>

diff --git a/Lib/test/test_asyncgen.py b/Lib/test/test_asyncgen.py
index 951c5502803789bfd79b0dd1c04d87eb398a6121..3576515522a70c56577ac9f957cdb914b74a3dda 100644 (file)
--- a/Lib/test/test_asyncgen.py
+++ b/Lib/test/test_asyncgen.py
@@ -1169,6 +1169,26 @@ class AsyncGenAsyncioTest(unittest.TestCase):
 
         self.loop.run_until_complete(run())
 
+    def test_sync_anext_raises_exception(self):
+        # See: https://github.com/python/cpython/issues/131670
+        msg = 'custom'
+        for exc_type in [
+            StopAsyncIteration,
+            StopIteration,
+            ValueError,
+            Exception,
+        ]:
+            exc = exc_type(msg)
+            with self.subTest(exc=exc):
+                class A:
+                    def __anext__(self):
+                        raise exc
+
+                with self.assertRaisesRegex(exc_type, msg):
+                    anext(A())
+                with self.assertRaisesRegex(exc_type, msg):
+                    anext(A(), 1)
+
     def test_async_gen_asyncio_anext_stopiteration(self):
         async def foo():
             try:

diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2025-03-24-19-38-53.gh-issue-131670.IffOZj.rst b/Misc/NEWS.d/next/Core_and_Builtins/2025-03-24-19-38-53.gh-issue-131670.IffOZj.rst
new file mode 100644 (file)
index 0000000..812a75a
--- /dev/null
+++ b/Misc/NEWS.d/next/Core_and_Builtins/2025-03-24-19-38-53.gh-issue-131670.IffOZj.rst
@@ -0,0 +1 @@
+Fix :func:`anext` failing on sync :meth:`~object.__anext__` raising an exception.

diff --git a/Python/bltinmodule.c b/Python/bltinmodule.c
index 29d4d10f1e41d25e6a92d1a67f692eb349f0b8eb..06bf4d38f9eab9f2eead8cb6528da33bad278f67 100644 (file)
--- a/Python/bltinmodule.c
+++ b/Python/bltinmodule.c
@@ -1737,6 +1737,9 @@ builtin_anext_impl(PyObject *module, PyObject *aiterator,
     }
 
     awaitable = (*t->tp_as_async->am_anext)(aiterator);
+    if (awaitable == NULL) {
+        return NULL;
+    }
     if (default_value == NULL) {
         return awaitable;
     }