bpo-36829: Add sys.unraisablehook() (GH-13187)

Add new sys.unraisablehook() function which can be overridden to
control how "unraisable exceptions" are handled. It is called when an
exception has occurred but there is no way for Python to handle it.
For example, when a destructor raises an exception or during garbage
collection (gc.collect()).

Changes:

* Add an internal UnraisableHookArgs type used to pass arguments to
  sys.unraisablehook.
* Add _PyErr_WriteUnraisableDefaultHook().
* The default hook now ignores exception on writing the traceback.
* test_sys now uses unittest.main() to automatically discover tests:
  remove test_main().
* Add _PyErr_Init().
* Fix PyErr_WriteUnraisable(): hold a strong reference to sys.stderr
  while using it

1 files changed, 4 insertions, 0 deletions

diff --git a/Include/internal/pycore_pylifecycle.h b/Include/internal/pycore_pylifecycle.h
index 4684ebe..07cf815 100644
--- a/Include/internal/pycore_pylifecycle.h
+++ b/Include/internal/pycore_pylifecycle.h
@@ -48,6 +48,7 @@ extern int _PySys_InitMain(
     PyInterpreterState *interp);
 extern _PyInitError _PyImport_Init(PyInterpreterState *interp);
 extern _PyInitError _PyExc_Init(void);
+extern _PyInitError _PyErr_Init(void);
 extern _PyInitError _PyBuiltins_AddExceptions(PyObject * bltinmod);
 extern _PyInitError _PyImportHooks_Init(void);
 extern int _PyFloat_Init(void);
@@ -100,8 +101,11 @@ PyAPI_FUNC(_PyInitError) _Py_PreInitializeFromCoreConfig(
     const _PyCoreConfig *coreconfig,
     const _PyArgv *args);
 
+
 PyAPI_FUNC(int) _Py_HandleSystemExit(int *exitcode_p);
 
+PyAPI_FUNC(PyObject*) _PyErr_WriteUnraisableDefaultHook(PyObject *unraisable);
+
 #ifdef __cplusplus
 }
 #endif