[3.12] gh-116735: Use MISSING for CALL event if argument is absen… (

#116873)

[3.12] gh-116735: Use `MISSING` for `CALL` event if argument is absent (GH-116737)

Lib/test/test_monitoring.py

@@ -1745,9 +1745,10 @@ def test_gh108976(self):
         sys.monitoring.set_events(0, 0)
 
     def test_call_function_ex(self):
-        def f(a, b):
+        def f(a=1, b=2):
             return a + b
         args = (1, 2)
+        empty_args = []
 
         call_data = []
         sys.monitoring.use_tool_id(0, "test")
@@ -1756,5 +1757,7 @@ def f(a, b):
         sys.monitoring.register_callback(0, E.CALL, lambda code, offset, callable, arg0: call_data.append((callable, arg0)))
         sys.monitoring.set_events(0, E.CALL)
         f(*args)
+        f(*empty_args)
         sys.monitoring.set_events(0, 0)
         self.assertEqual(call_data[0], (f, 1))
+        self.assertEqual(call_data[1], (f, sys.monitoring.MISSING))

Misc/NEWS.d/next/Core and Builtins/2024-03-13-16-55-25.gh-issue-116735.o3w6y8.rst

@@ -0,0 +1 @@
+For ``INSTRUMENTED_CALL_FUNCTION_EX``, set ``arg0`` to ``sys.monitoring.MISSING`` instead of ``None`` for :monitoring-event:`CALL` event.

Python/bytecodes.c

@@ -3209,7 +3209,7 @@ dummy_func(
             EVAL_CALL_STAT_INC_IF_FUNCTION(EVAL_CALL_FUNCTION_EX, func);
             if (opcode == INSTRUMENTED_CALL_FUNCTION_EX) {
                 PyObject *arg = PyTuple_GET_SIZE(callargs) > 0 ?
-                    PyTuple_GET_ITEM(callargs, 0) : Py_None;
+                    PyTuple_GET_ITEM(callargs, 0) : &_PyInstrumentation_MISSING;
                 int err = _Py_call_instrumentation_2args(
                     tstate, PY_MONITORING_EVENT_CALL,
                     frame, next_instr-1, func, arg);