[Python-checkins] gh-104770: Let generator.close() return value (#104771)

[gvanrossum]

https://github.com/python/cpython/commit/d56c933992c86986bd58eb3880aed0ed1b0cadc9
commit: d56c933992c86986bd58eb3880aed0ed1b0cadc9
branch: main
author: Nicolas Tessore <n.tessore at ucl.ac.uk>
committer: gvanrossum <gvanrossum at gmail.com>
date: 2023-05-23T13:51:56-07:00
summary:

gh-104770: Let generator.close() return value (#104771)

Co-authored-by: Irit Katriel <1055913+iritkatriel at users.noreply.github.com>

files:
A Misc/NEWS.d/next/Core and Builtins/2023-05-23-00-36-02.gh-issue-104770.poSkyY.rst
M Doc/reference/expressions.rst
M Lib/test/test_generators.py
M Objects/genobject.c

diff --git a/Doc/reference/expressions.rst b/Doc/reference/expressions.rst
index b97a08f25d92..0c700f908d68 100644
--- a/Doc/reference/expressions.rst
+++ b/Doc/reference/expressions.rst
@@ -595,12 +595,19 @@ is already executing raises a :exc:`ValueError` exception.
 .. method:: generator.close()
 
    Raises a :exc:`GeneratorExit` at the point where the generator function was
-   paused.  If the generator function then exits gracefully, is already closed,
-   or raises :exc:`GeneratorExit` (by not catching the exception), close
-   returns to its caller.  If the generator yields a value, a
-   :exc:`RuntimeError` is raised.  If the generator raises any other exception,
-   it is propagated to the caller.  :meth:`close` does nothing if the generator
-   has already exited due to an exception or normal exit.
+   paused.  If the generator function catches the exception and returns a
+   value, this value is returned from :meth:`close`.  If the generator function
+   is already closed, or raises :exc:`GeneratorExit` (by not catching the
+   exception), :meth:`close` returns :const:`None`.  If the generator yields a
+   value, a :exc:`RuntimeError` is raised.  If the generator raises any other
+   exception, it is propagated to the caller.  If the generator has already
+   exited due to an exception or normal exit, :meth:`close` returns
+   :const:`None` and has no other effect.
+
+   .. versionchanged:: 3.13
+
+      If a generator returns a value upon being closed, the value is returned
+      by :meth:`close`.
 
 .. index:: single: yield; examples
 
diff --git a/Lib/test/test_generators.py b/Lib/test/test_generators.py
index 31680b5a92e0..a8a344ab8de4 100644
--- a/Lib/test/test_generators.py
+++ b/Lib/test/test_generators.py
@@ -451,6 +451,88 @@ def g():
         self.assertEqual(cm.exception.value.value, 2)
 
 
+class GeneratorCloseTest(unittest.TestCase):
+
+    def test_close_no_return_value(self):
+        def f():
+            yield
+
+        gen = f()
+        gen.send(None)
+        self.assertIsNone(gen.close())
+
+    def test_close_return_value(self):
+        def f():
+            try:
+                yield
+                # close() raises GeneratorExit here, which is caught
+            except GeneratorExit:
+                return 0
+
+        gen = f()
+        gen.send(None)
+        self.assertEqual(gen.close(), 0)
+
+    def test_close_not_catching_exit(self):
+        def f():
+            yield
+            # close() raises GeneratorExit here, which isn't caught and
+            # therefore propagates -- no return value
+            return 0
+
+        gen = f()
+        gen.send(None)
+        self.assertIsNone(gen.close())
+
+    def test_close_not_started(self):
+        def f():
+            try:
+                yield
+            except GeneratorExit:
+                return 0
+
+        gen = f()
+        self.assertIsNone(gen.close())
+
+    def test_close_exhausted(self):
+        def f():
+            try:
+                yield
+            except GeneratorExit:
+                return 0
+
+        gen = f()
+        next(gen)
+        with self.assertRaises(StopIteration):
+            next(gen)
+        self.assertIsNone(gen.close())
+
+    def test_close_closed(self):
+        def f():
+            try:
+                yield
+            except GeneratorExit:
+                return 0
+
+        gen = f()
+        gen.send(None)
+        self.assertEqual(gen.close(), 0)
+        self.assertIsNone(gen.close())
+
+    def test_close_raises(self):
+        def f():
+            try:
+                yield
+            except GeneratorExit:
+                pass
+            raise RuntimeError
+
+        gen = f()
+        gen.send(None)
+        with self.assertRaises(RuntimeError):
+            gen.close()
+
+
 class GeneratorThrowTest(unittest.TestCase):
 
     def test_exception_context_with_yield(self):
diff --git a/Misc/NEWS.d/next/Core and Builtins/2023-05-23-00-36-02.gh-issue-104770.poSkyY.rst b/Misc/NEWS.d/next/Core and Builtins/2023-05-23-00-36-02.gh-issue-104770.poSkyY.rst
new file mode 100644
index 000000000000..2103fb7d61c2
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2023-05-23-00-36-02.gh-issue-104770.poSkyY.rst	
@@ -0,0 +1,2 @@
+If a generator returns a value upon being closed, the value is now returned
+by :meth:`generator.close`.
diff --git a/Objects/genobject.c b/Objects/genobject.c
index 9252c6549345..1abfc83ab678 100644
--- a/Objects/genobject.c
+++ b/Objects/genobject.c
@@ -408,11 +408,16 @@ gen_close(PyGenObject *gen, PyObject *args)
         PyErr_SetString(PyExc_RuntimeError, msg);
         return NULL;
     }
-    if (PyErr_ExceptionMatches(PyExc_StopIteration)
-        || PyErr_ExceptionMatches(PyExc_GeneratorExit)) {
-        PyErr_Clear();          /* ignore these errors */
+    assert(PyErr_Occurred());
+    if (PyErr_ExceptionMatches(PyExc_GeneratorExit)) {
+        PyErr_Clear();          /* ignore this error */
         Py_RETURN_NONE;
     }
+    /* if the generator returned a value while closing, StopIteration was
+     * raised in gen_send_ex() above; retrieve and return the value here */
+    if (_PyGen_FetchStopIterationValue(&retval) == 0) {
+        return retval;
+    }
     return NULL;
 }