Issue #22290: PyObject_Call() now fails with an assertion error when called

with an exception set. This new assertion helps to understand if the exception
was already set before calling the function or raised by the function.

Objects/abstract.c

@@ -2074,6 +2074,11 @@ PyObject_Call(PyObject *func, PyObject *arg, PyObject *kw)
 {
     ternaryfunc call;
 
+    /* PyObject_Call() must not be called with an exception set,
+       because it may clear it (directly or indirectly) and so the
+       caller looses its exception */
+    assert(!PyErr_Occurred());
+
     if ((call = func->ob_type->tp_call) != NULL) {
         PyObject *result;
         if (Py_EnterRecursiveCall(" while calling a Python object"))