[Python-checkins] bpo-38013: make async_generator_athrow object tolerant to throwing exceptions (GH-16070)

[Miss Islington (bot)]

https://github.com/python/cpython/commit/fc022f04b41a79cacdff380435c30c8042c82b99
commit: fc022f04b41a79cacdff380435c30c8042c82b99
branch: 3.7
author: Miss Islington (bot) <31488909+miss-islington at users.noreply.github.com>
committer: GitHub <noreply at github.com>
date: 2019-09-17T06:19:25-07:00
summary:

bpo-38013: make async_generator_athrow object tolerant to throwing exceptions (GH-16070)


Even when the helper is not started yet.

This behavior follows conventional generator one.
There is no reason for `async_generator_athrow` to handle `gen.throw()` differently.

https://bugs.python.org/issue38013
(cherry picked from commit c275312a6284bd319ea33c9abd7e15c230eca43f)

Co-authored-by: Andrew Svetlov <andrew.svetlov at gmail.com>

files:
A Misc/NEWS.d/next/Core and Builtins/2019-09-12-19-50-01.bpo-38013.I7btD0.rst
M Lib/test/test_asyncgen.py
M Objects/genobject.c

diff --git a/Lib/test/test_asyncgen.py b/Lib/test/test_asyncgen.py
index 5a36423dc97a..94c2633f330a 100644
--- a/Lib/test/test_asyncgen.py
+++ b/Lib/test/test_asyncgen.py
@@ -1068,6 +1068,28 @@ def make_arange(n):
         res = self.loop.run_until_complete(run())
         self.assertEqual(res, [i * 2 for i in range(1, 10)])
 
+    def test_asyncgen_nonstarted_hooks_are_cancellable(self):
+        # See https://bugs.python.org/issue38013
+        messages = []
+
+        def exception_handler(loop, context):
+            messages.append(context)
+
+        async def async_iterate():
+            yield 1
+            yield 2
+
+        async def main():
+            loop = asyncio.get_running_loop()
+            loop.set_exception_handler(exception_handler)
+
+            async for i in async_iterate():
+                break
+
+        asyncio.run(main())
+
+        self.assertEqual([], messages)
+
 
 if __name__ == "__main__":
     unittest.main()
diff --git a/Misc/NEWS.d/next/Core and Builtins/2019-09-12-19-50-01.bpo-38013.I7btD0.rst b/Misc/NEWS.d/next/Core and Builtins/2019-09-12-19-50-01.bpo-38013.I7btD0.rst
new file mode 100644
index 000000000000..a61aa48ff1ef
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2019-09-12-19-50-01.bpo-38013.I7btD0.rst	
@@ -0,0 +1,3 @@
+Allow to call ``async_generator_athrow().throw(...)`` even for non-started
+async generator helper. It fixes annoying warning at the end of
+:func:`asyncio.run` call.
diff --git a/Objects/genobject.c b/Objects/genobject.c
index b0e877072c78..8a978b1a1fe0 100644
--- a/Objects/genobject.c
+++ b/Objects/genobject.c
@@ -1905,11 +1905,6 @@ async_gen_athrow_throw(PyAsyncGenAThrow *o, PyObject *args)
 {
     PyObject *retval;
 
-    if (o->agt_state == AWAITABLE_STATE_INIT) {
-        PyErr_SetString(PyExc_RuntimeError, NON_INIT_CORO_MSG);
-        return NULL;
-    }
-
     if (o->agt_state == AWAITABLE_STATE_CLOSED) {
         PyErr_SetNone(PyExc_StopIteration);
         return NULL;