pythongh-131670: Fix crash in anext() when __anext__ is sync and raises

sobolevn · sobolevn · commit 6862fb495960 · 2025-03-24T19:42:40.000+03:00
diff --git a/Lib/test/test_asyncgen.py b/Lib/test/test_asyncgen.py
@@ -1169,6 +1169,25 @@ async def run():
 
         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 in [
+            StopAsyncIteration(msg),
+            StopIteration(msg),
+            ValueError(msg),
+            Exception(msg),
+        ]:
+            with self.subTest(exc=exc):
+                class A:
+                    def __anext__(self):
+                        raise exc
+
+                with self.assertRaisesRegex(type(exc), msg):
+                    anext(A())
+                with self.assertRaisesRegex(type(exc), 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
@@ -0,0 +1,2 @@
+Fix :func:`anext` failing on sync :meth:`~object.__anext__` that raises
+:exc:`StopAsyncIteration`.
diff --git a/Python/bltinmodule.c b/Python/bltinmodule.c
@@ -1837,6 +1837,9 @@ 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;
     }

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,2 @@`
	`1`	+Fix :func:`anext` failing on sync :meth:`~object.__anext__` that raises
	`2`	+:exc:`StopAsyncIteration`.
Original file line number	Diff line number	Diff line change
`@@ -1837,6 +1837,9 @@ builtin_anext_impl(PyObject module, PyObject aiterator,`
`1837`	`1837`	`}`
`1838`	`1838`
`1839`	`1839`	`awaitable = (*t->tp_as_async->am_anext)(aiterator);`
	`1840`	`+ if (awaitable == NULL) {`
	`1841`	`+ return NULL;`
	`1842`	`+ }`
`1840`	`1843`	`if (default_value == NULL) {`
`1841`	`1844`	`return awaitable;`
`1842`	`1845`	`}`