Implement "gen.gi_frame" and "coro.cr_frame" attributes on generators and...

Implement "gen.gi_frame" and "coro.cr_frame" attributes on generators and coroutines that return an inspectable (although otherwise dead) frame object.
Closes #2306.

CHANGES.rst

@@ -20,6 +20,10 @@ Features added
 * Properties can be defined for external extension types.
   Patch by Matti Picus.  (Github issue #2640)
 
+* The attributes ``gen.gi_frame`` and ``coro.cr_frame`` of Cython compiled
+  generators and coroutines now return an actual frame object for introspection.
+  (Github issue #2306)
+
 * The builtin ``abs()`` function can now be used on C numbers in nogil code.
   Patch by Elliott Sales de Andrade.  (Github issue #2748)
 

Cython/Utility/Coroutine.c

@@ -388,6 +388,7 @@ typedef struct {
     PyObject *gi_qualname;
     PyObject *gi_modulename;
     PyObject *gi_code;
+    PyObject *gi_frame;
     int resume_label;
     // using T_BOOL for property below requires char value
     char is_running;
@@ -1110,6 +1111,7 @@ static int __Pyx_Coroutine_clear(PyObject *self) {
     }
 #endif
     Py_CLEAR(gen->gi_code);
+    Py_CLEAR(gen->gi_frame);
     Py_CLEAR(gen->gi_name);
     Py_CLEAR(gen->gi_qualname);
     Py_CLEAR(gen->gi_modulename);
@@ -1342,6 +1344,30 @@ __Pyx_Coroutine_set_qualname(__pyx_CoroutineObject *self, PyObject *value, CYTHO
     return 0;
 }
 
+static PyObject *
+__Pyx_Coroutine_get_frame(__pyx_CoroutineObject *self, CYTHON_UNUSED void *context)
+{
+    PyObject *frame = self->gi_frame;
+    if (!frame) {
+        if (unlikely(!self->gi_code)) {
+            // Avoid doing something stupid, e.g. during garbage collection.
+            Py_RETURN_NONE;
+        }
+        frame = (PyObject *) PyFrame_New(
+            PyThreadState_Get(),            /*PyThreadState *tstate,*/
+            (PyCodeObject*) self->gi_code,  /*PyCodeObject *code,*/
+            $moddict_cname,                 /*PyObject *globals,*/
+            0                               /*PyObject *locals*/
+        );
+        if (unlikely(!frame))
+            return NULL;
+        // keep the frame cached once it's created
+        self->gi_frame = frame;
+    }
+    Py_INCREF(frame);
+    return frame;
+}
+
 static __pyx_CoroutineObject *__Pyx__Coroutine_New(
             PyTypeObject* type, __pyx_coroutine_body_t body, PyObject *code, PyObject *closure,
             PyObject *name, PyObject *qualname, PyObject *module_name) {
@@ -1376,6 +1402,7 @@ static __pyx_CoroutineObject *__Pyx__Coroutine_NewInit(
     gen->gi_modulename = module_name;
     Py_XINCREF(code);
     gen->gi_code = code;
+    gen->gi_frame = NULL;
 
     PyObject_GC_Track(gen);
     return gen;
@@ -1525,13 +1552,6 @@ static PyObject *__Pyx_Coroutine_await(PyObject *coroutine) {
 }
 #endif
 
-static PyObject *
-__Pyx_Coroutine_get_frame(CYTHON_UNUSED __pyx_CoroutineObject *self, CYTHON_UNUSED void *context)
-{
-    // Fake implementation that always returns None, but at least does not raise an AttributeError.
-    Py_RETURN_NONE;
-}
-
 #if CYTHON_COMPILING_IN_CPYTHON && PY_MAJOR_VERSION >= 3 && PY_VERSION_HEX < 0x030500B1
 static PyObject *__Pyx_Coroutine_compare(PyObject *obj, PyObject *other, int op) {
     PyObject* result;
@@ -1799,6 +1819,8 @@ static PyGetSetDef __pyx_Generator_getsets[] = {
      (char*) PyDoc_STR("name of the generator"), 0},
     {(char *) "__qualname__", (getter)__Pyx_Coroutine_get_qualname, (setter)__Pyx_Coroutine_set_qualname,
      (char*) PyDoc_STR("qualified name of the generator"), 0},
+    {(char *) "gi_frame", (getter)__Pyx_Coroutine_get_frame, NULL,
+     (char*) PyDoc_STR("Frame of the coroutine"), 0},
     {0, 0, 0, 0, 0}
 };
 

tests/run/coroutines.py

+# cython: language_level=3
+# mode: run
+# tag: pep492, pure3.5
+
+
+async def test_coroutine_frame(awaitable):
+    """
+    >>> class Awaitable(object):
+    ...     def __await__(self):
+    ...         return iter([2])
+
+    >>> coro = test_coroutine_frame(Awaitable())
+    >>> import types
+    >>> isinstance(coro.cr_frame, types.FrameType) or coro.cr_frame
+    True
+    >>> coro.cr_frame is coro.cr_frame  # assert that it's cached
+    True
+    >>> coro.cr_frame.f_code is not None
+    True
+    >>> code_obj = coro.cr_frame.f_code
+    >>> code_obj.co_argcount
+    1
+    >>> code_obj.co_varnames
+    ('awaitable', 'b')
+
+    >>> next(coro.__await__())  # avoid "not awaited" warning
+    2
+    """
+    b = await awaitable
+    return b

tests/run/generators.pyx

@@ -502,3 +502,23 @@ def test_generator_abc():
     True
     """
     yield 1
+
+
+def test_generator_frame(a=1):
+    """
+    >>> gen = test_generator_frame()
+    >>> import types
+    >>> isinstance(gen.gi_frame, types.FrameType) or gen.gi_frame
+    True
+    >>> gen.gi_frame is gen.gi_frame  # assert that it's cached
+    True
+    >>> gen.gi_frame.f_code is not None
+    True
+    >>> code_obj = gen.gi_frame.f_code
+    >>> code_obj.co_argcount
+    1
+    >>> code_obj.co_varnames
+    ('a', 'b')
+    """
+    b = a + 1
+    yield b