exceptions.c

/*
 * New exceptions.c written in Iceland by Richard Jones and Georg Brandl.
 *
 * Thanks go to Tim Peters and Michael Hudson for debugging.
 */

#include <Python.h>
#include <stdbool.h>
#include "pycore_abstract.h"      // _PyObject_RealIsSubclass()
#include "pycore_ceval.h"         // _Py_EnterRecursiveCall
#include "pycore_exceptions.h"    // struct _Py_exc_state
#include "pycore_initconfig.h"
#include "pycore_modsupport.h"    // _PyArg_NoKeywords()
#include "pycore_object.h"
#include "pycore_pyerrors.h"      // struct _PyErr_SetRaisedException
#include "pycore_tuple.h"         // _PyTuple_FromArray()

#include "osdefs.h"               // SEP
#include "clinic/exceptions.c.h"


/*[clinic input]
class BaseException "PyBaseExceptionObject *" "&PyExc_BaseException"
class BaseExceptionGroup "PyBaseExceptionGroupObject *" "&PyExc_BaseExceptionGroup"
[clinic start generated code]*/
/*[clinic end generated code: output=da39a3ee5e6b4b0d input=b7c45e78cff8edc3]*/


/* Compatibility aliases */
PyObject *PyExc_EnvironmentError = NULL;  // borrowed ref
PyObject *PyExc_IOError = NULL;  // borrowed ref
#ifdef MS_WINDOWS
PyObject *PyExc_WindowsError = NULL;  // borrowed ref
#endif


static struct _Py_exc_state*
get_exc_state(void)
{
    PyInterpreterState *interp = _PyInterpreterState_GET();
    return &interp->exc_state;
}


/* NOTE: If the exception class hierarchy changes, don't forget to update
 * Lib/test/exception_hierarchy.txt
 */

static inline PyBaseExceptionObject *
PyBaseExceptionObject_CAST(PyObject *exc)
{
    assert(PyExceptionInstance_Check(exc));
    return (PyBaseExceptionObject *)exc;
}

/*
 *    BaseException
 */
static PyObject *
BaseException_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
    PyBaseExceptionObject *self;

    self = (PyBaseExceptionObject *)type->tp_alloc(type, 0);
    if (!self)
        return NULL;
    /* the dict is created on the fly in PyObject_GenericSetAttr */
    self->dict = NULL;
    self->notes = NULL;
    self->traceback = self->cause = self->context = NULL;
    self->suppress_context = 0;

    if (args) {
        self->args = Py_NewRef(args);
        return (PyObject *)self;
    }

    self->args = PyTuple_New(0);
    if (!self->args) {
        Py_DECREF(self);
        return NULL;
    }

    return (PyObject *)self;
}

static int
BaseException_init(PyObject *op, PyObject *args, PyObject *kwds)
{
    PyBaseExceptionObject *self = PyBaseExceptionObject_CAST(op);
    if (!_PyArg_NoKeywords(Py_TYPE(self)->tp_name, kwds))
        return -1;

    Py_XSETREF(self->args, Py_NewRef(args));
    return 0;
}


static PyObject *
BaseException_vectorcall(PyObject *type_obj, PyObject * const*args,
                         size_t nargsf, PyObject *kwnames)
{
    PyTypeObject *type = _PyType_CAST(type_obj);
    if (!_PyArg_NoKwnames(type->tp_name, kwnames)) {
        return NULL;
    }

    PyBaseExceptionObject *self;
    self = (PyBaseExceptionObject *)type->tp_alloc(type, 0);
    if (!self) {
        return NULL;
    }

    // The dict is created on the fly in PyObject_GenericSetAttr()
    self->dict = NULL;
    self->notes = NULL;
    self->traceback = NULL;
    self->cause = NULL;
    self->context = NULL;
    self->suppress_context = 0;

    self->args = _PyTuple_FromArray(args, PyVectorcall_NARGS(nargsf));
    if (!self->args) {
        Py_DECREF(self);
        return NULL;
    }

    return (PyObject *)self;
}


static int
BaseException_clear(PyObject *op)
{
    PyBaseExceptionObject *self = PyBaseExceptionObject_CAST(op);
    Py_CLEAR(self->dict);
    Py_CLEAR(self->args);
    Py_CLEAR(self->notes);
    Py_CLEAR(self->traceback);
    Py_CLEAR(self->cause);
    Py_CLEAR(self->context);
    return 0;
}

static void
BaseException_dealloc(PyObject *op)
{
    PyBaseExceptionObject *self = PyBaseExceptionObject_CAST(op);
    PyObject_GC_UnTrack(self);
    // bpo-44348: The trashcan mechanism prevents stack overflow when deleting
    // long chains of exceptions. For example, exceptions can be chained
    // through the __context__ attributes or the __traceback__ attribute.
    (void)BaseException_clear(op);
    Py_TYPE(self)->tp_free(self);
}

static int
BaseException_traverse(PyObject *op, visitproc visit, void *arg)
{
    PyBaseExceptionObject *self = PyBaseExceptionObject_CAST(op);
    Py_VISIT(self->dict);
    Py_VISIT(self->args);
    Py_VISIT(self->notes);
    Py_VISIT(self->traceback);
    Py_VISIT(self->cause);
    Py_VISIT(self->context);
    return 0;
}

static PyObject *
BaseException_str(PyObject *op)
{
    PyBaseExceptionObject *self = PyBaseExceptionObject_CAST(op);

    PyObject *res;
    Py_BEGIN_CRITICAL_SECTION(self);
    switch (PyTuple_GET_SIZE(self->args)) {
    case 0:
        res = Py_GetConstant(Py_CONSTANT_EMPTY_STR);
        break;
    case 1:
        res = PyObject_Str(PyTuple_GET_ITEM(self->args, 0));
        break;
    default:
        res = PyObject_Str(self->args);
        break;
    }
    Py_END_CRITICAL_SECTION();
    return res;
}

static PyObject *
BaseException_repr(PyObject *op)
{

    PyBaseExceptionObject *self = PyBaseExceptionObject_CAST(op);

    PyObject *res;
    Py_BEGIN_CRITICAL_SECTION(self);
    const char *name = _PyType_Name(Py_TYPE(self));
    if (PyTuple_GET_SIZE(self->args) == 1) {
        res = PyUnicode_FromFormat("%s(%R)", name,
                                    PyTuple_GET_ITEM(self->args, 0));
    }
    else {
        res = PyUnicode_FromFormat("%s%R", name, self->args);
    }
    Py_END_CRITICAL_SECTION();
    return res;
}

/* Pickling support */

/*[clinic input]
@critical_section
BaseException.__reduce__
[clinic start generated code]*/

static PyObject *
BaseException___reduce___impl(PyBaseExceptionObject *self)
/*[clinic end generated code: output=af87c1247ef98748 input=283be5a10d9c964f]*/
{
    if (self->args && self->dict)
        return PyTuple_Pack(3, Py_TYPE(self), self->args, self->dict);
    else
        return PyTuple_Pack(2, Py_TYPE(self), self->args);
}

/*
 * Needed for backward compatibility, since exceptions used to store
 * all their attributes in the __dict__. Code is taken from cPickle's
 * load_build function.
 */

/*[clinic input]
@critical_section
BaseException.__setstate__
    state: object
    /
[clinic start generated code]*/

static PyObject *
BaseException___setstate___impl(PyBaseExceptionObject *self, PyObject *state)
/*[clinic end generated code: output=f3834889950453ab input=5524b61cfe9b9856]*/
{
    PyObject *d_key, *d_value;
    Py_ssize_t i = 0;

    if (state != Py_None) {
        if (!PyDict_Check(state)) {
            PyErr_SetString(PyExc_TypeError, "state is not a dictionary");
            return NULL;
        }
        while (PyDict_Next(state, &i, &d_key, &d_value)) {
            Py_INCREF(d_key);
            Py_INCREF(d_value);
            int res = PyObject_SetAttr((PyObject *)self, d_key, d_value);
            Py_DECREF(d_value);
            Py_DECREF(d_key);
            if (res < 0) {
                return NULL;
            }
        }
    }
    Py_RETURN_NONE;
}


/*[clinic input]
@critical_section
BaseException.with_traceback
    tb: object
    /

Set self.__traceback__ to tb and return self.
[clinic start generated code]*/

static PyObject *
BaseException_with_traceback_impl(PyBaseExceptionObject *self, PyObject *tb)
/*[clinic end generated code: output=81e92f2387927f10 input=b5fb64d834717e36]*/
{
    if (BaseException___traceback___set_impl(self, tb) < 0){
        return NULL;
    }
    return Py_NewRef(self);
}

/*[clinic input]
@critical_section
BaseException.add_note
    note: object(subclass_of="&PyUnicode_Type")
    /

Add a note to the exception
[clinic start generated code]*/

static PyObject *
BaseException_add_note_impl(PyBaseExceptionObject *self, PyObject *note)
/*[clinic end generated code: output=fb7cbcba611c187b input=e60a6b6e9596acaf]*/
{
    PyObject *notes;
    if (PyObject_GetOptionalAttr((PyObject *)self, &_Py_ID(__notes__), &notes) < 0) {
        return NULL;
    }
    if (notes == NULL) {
        notes = PyList_New(0);
        if (notes == NULL) {
            return NULL;
        }
        if (PyObject_SetAttr((PyObject *)self, &_Py_ID(__notes__), notes) < 0) {
            Py_DECREF(notes);
            return NULL;
        }
    }
    else if (!PyList_Check(notes)) {
        Py_DECREF(notes);
        PyErr_SetString(PyExc_TypeError, "Cannot add note: __notes__ is not a list");
        return NULL;
    }
    if (PyList_Append(notes, note) < 0) {
        Py_DECREF(notes);
        return NULL;
    }
    Py_DECREF(notes);
    Py_RETURN_NONE;
}

static PyMethodDef BaseException_methods[] = {
    BASEEXCEPTION___REDUCE___METHODDEF
    BASEEXCEPTION___SETSTATE___METHODDEF
    BASEEXCEPTION_WITH_TRACEBACK_METHODDEF
    BASEEXCEPTION_ADD_NOTE_METHODDEF
    {NULL, NULL, 0, NULL},
};

/*[clinic input]
@critical_section
@getter
BaseException.args
[clinic start generated code]*/

static PyObject *
BaseException_args_get_impl(PyBaseExceptionObject *self)
/*[clinic end generated code: output=e02e34e35cf4d677 input=64282386e4d7822d]*/
{
    if (self->args == NULL) {
        Py_RETURN_NONE;
    }
    return Py_NewRef(self->args);
}

/*[clinic input]
@critical_section
@setter
BaseException.args
[clinic start generated code]*/

static int
BaseException_args_set_impl(PyBaseExceptionObject *self, PyObject *value)
/*[clinic end generated code: output=331137e11d8f9e80 input=2400047ea5970a84]*/
{
    PyObject *seq;
    if (value == NULL) {
        PyErr_SetString(PyExc_TypeError, "args may not be deleted");
        return -1;
    }
    seq = PySequence_Tuple(value);
    if (!seq)
        return -1;
    Py_XSETREF(self->args, seq);
    return 0;
}

/*[clinic input]
@critical_section
@getter
BaseException.__traceback__
[clinic start generated code]*/

static PyObject *
BaseException___traceback___get_impl(PyBaseExceptionObject *self)
/*[clinic end generated code: output=17cf874a52339398 input=a2277f0de62170cf]*/
{
    if (self->traceback == NULL) {
        Py_RETURN_NONE;
    }
    return Py_NewRef(self->traceback);
}


/*[clinic input]
@critical_section
@setter
BaseException.__traceback__
[clinic start generated code]*/

static int
BaseException___traceback___set_impl(PyBaseExceptionObject *self,
                                     PyObject *value)
/*[clinic end generated code: output=a82c86d9f29f48f0 input=12676035676badad]*/
{
    if (value == NULL) {
        PyErr_SetString(PyExc_TypeError, "__traceback__ may not be deleted");
        return -1;
    }
    if (PyTraceBack_Check(value)) {
        Py_XSETREF(self->traceback, Py_NewRef(value));
    }
    else if (value == Py_None) {
        Py_CLEAR(self->traceback);
    }
    else {
        PyErr_SetString(PyExc_TypeError,
                        "__traceback__ must be a traceback or None");
        return -1;
    }
    return 0;
}

/*[clinic input]
@critical_section
@getter
BaseException.__context__
[clinic start generated code]*/

static PyObject *
BaseException___context___get_impl(PyBaseExceptionObject *self)
/*[clinic end generated code: output=6ec5d296ce8d1c93 input=b2d22687937e66ab]*/
{
    if (self->context == NULL) {
        Py_RETURN_NONE;
    }
    return Py_NewRef(self->context);
}

/*[clinic input]
@critical_section
@setter
BaseException.__context__
[clinic start generated code]*/

static int
BaseException___context___set_impl(PyBaseExceptionObject *self,
                                   PyObject *value)
/*[clinic end generated code: output=b4cb52dcca1da3bd input=c0971adf47fa1858]*/
{
    if (value == NULL) {
        PyErr_SetString(PyExc_TypeError, "__context__ may not be deleted");
        return -1;
    } else if (value == Py_None) {
        value = NULL;
    } else if (!PyExceptionInstance_Check(value)) {
        PyErr_SetString(PyExc_TypeError, "exception context must be None "
                        "or derive from BaseException");
        return -1;
    } else {
        Py_INCREF(value);
    }
    Py_XSETREF(self->context, value);
    return 0;
}

/*[clinic input]
@critical_section
@getter
BaseException.__cause__
[clinic start generated code]*/

static PyObject *
BaseException___cause___get_impl(PyBaseExceptionObject *self)
/*[clinic end generated code: output=987f6c4d8a0bdbab input=40e0eac427b6e602]*/
{
    if (self->cause == NULL) {
        Py_RETURN_NONE;
    }
    return Py_NewRef(self->cause);
}

/*[clinic input]
@critical_section
@setter
BaseException.__cause__
[clinic start generated code]*/

static int
BaseException___cause___set_impl(PyBaseExceptionObject *self,
                                 PyObject *value)
/*[clinic end generated code: output=6161315398aaf541 input=e1b403c0bde3f62a]*/
{
    if (value == NULL) {
        PyErr_SetString(PyExc_TypeError, "__cause__ may not be deleted");
        return -1;
    } else if (value == Py_None) {
        value = NULL;
    } else if (!PyExceptionInstance_Check(value)) {
        PyErr_SetString(PyExc_TypeError, "exception cause must be None "
                        "or derive from BaseException");
        return -1;
    } else {
        /* PyException_SetCause steals this reference */
        Py_INCREF(value);
    }
    PyException_SetCause((PyObject *)self, value);
    return 0;
}


static PyGetSetDef BaseException_getset[] = {
    {"__dict__", PyObject_GenericGetDict, PyObject_GenericSetDict},
     BASEEXCEPTION_ARGS_GETSETDEF
     BASEEXCEPTION___TRACEBACK___GETSETDEF
     BASEEXCEPTION___CONTEXT___GETSETDEF
     BASEEXCEPTION___CAUSE___GETSETDEF
    {NULL},
};


PyObject *
PyException_GetTraceback(PyObject *self)
{
    PyObject *traceback;
    Py_BEGIN_CRITICAL_SECTION(self);
    traceback = Py_XNewRef(PyBaseExceptionObject_CAST(self)->traceback);
    Py_END_CRITICAL_SECTION();
    return traceback;
}


int
PyException_SetTraceback(PyObject *self, PyObject *tb)
{
    int res;
    Py_BEGIN_CRITICAL_SECTION(self);
    res = BaseException___traceback___set_impl(PyBaseExceptionObject_CAST(self), tb);
    Py_END_CRITICAL_SECTION();
    return res;
}

PyObject *
PyException_GetCause(PyObject *self)
{
    PyObject *cause;
    Py_BEGIN_CRITICAL_SECTION(self);
    cause = Py_XNewRef(PyBaseExceptionObject_CAST(self)->cause);
    Py_END_CRITICAL_SECTION();
    return cause;
}

/* Steals a reference to cause */
void
PyException_SetCause(PyObject *self, PyObject *cause)
{
    Py_BEGIN_CRITICAL_SECTION(self);
    PyBaseExceptionObject *base_self = PyBaseExceptionObject_CAST(self);
    base_self->suppress_context = 1;
    Py_XSETREF(base_self->cause, cause);
    Py_END_CRITICAL_SECTION();
}

PyObject *
PyException_GetContext(PyObject *self)
{
    PyObject *context;
    Py_BEGIN_CRITICAL_SECTION(self);
    context = Py_XNewRef(PyBaseExceptionObject_CAST(self)->context);
    Py_END_CRITICAL_SECTION();
    return context;
}

/* Steals a reference to context */
void
PyException_SetContext(PyObject *self, PyObject *context)
{
    Py_BEGIN_CRITICAL_SECTION(self);
    Py_XSETREF(PyBaseExceptionObject_CAST(self)->context, context);
    Py_END_CRITICAL_SECTION();
}

PyObject *
PyException_GetArgs(PyObject *self)
{
    PyObject *args;
    Py_BEGIN_CRITICAL_SECTION(self);
    args = Py_NewRef(PyBaseExceptionObject_CAST(self)->args);
    Py_END_CRITICAL_SECTION();
    return args;
}

void
PyException_SetArgs(PyObject *self, PyObject *args)
{
    Py_BEGIN_CRITICAL_SECTION(self);
    Py_INCREF(args);
    Py_XSETREF(PyBaseExceptionObject_CAST(self)->args, args);
    Py_END_CRITICAL_SECTION();
}

const char *
PyExceptionClass_Name(PyObject *ob)
{
    assert(PyExceptionClass_Check(ob));
    return ((PyTypeObject*)ob)->tp_name;
}

static struct PyMemberDef BaseException_members[] = {
    {"__suppress_context__", Py_T_BOOL,
     offsetof(PyBaseExceptionObject, suppress_context)},
    {NULL}
};


static PyTypeObject _PyExc_BaseException = {
    PyVarObject_HEAD_INIT(NULL, 0)
    "BaseException", /*tp_name*/
    sizeof(PyBaseExceptionObject), /*tp_basicsize*/
    0,                          /*tp_itemsize*/
    BaseException_dealloc,      /*tp_dealloc*/
    0,                          /*tp_vectorcall_offset*/
    0,                          /*tp_getattr*/
    0,                          /*tp_setattr*/
    0,                          /*tp_as_async*/
    BaseException_repr,         /*tp_repr*/
    0,                          /*tp_as_number*/
    0,                          /*tp_as_sequence*/
    0,                          /*tp_as_mapping*/
    0,                          /*tp_hash */
    0,                          /*tp_call*/
    BaseException_str,          /*tp_str*/
    PyObject_GenericGetAttr,    /*tp_getattro*/
    PyObject_GenericSetAttr,    /*tp_setattro*/
    0,                          /*tp_as_buffer*/
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HAVE_GC |
        Py_TPFLAGS_BASE_EXC_SUBCLASS,  /*tp_flags*/
    PyDoc_STR("Common base class for all exceptions"), /* tp_doc */
    BaseException_traverse,     /* tp_traverse */
    BaseException_clear,        /* tp_clear */
    0,                          /* tp_richcompare */
    0,                          /* tp_weaklistoffset */
    0,                          /* tp_iter */
    0,                          /* tp_iternext */
    BaseException_methods,      /* tp_methods */
    BaseException_members,      /* tp_members */
    BaseException_getset,       /* tp_getset */
    0,                          /* tp_base */
    0,                          /* tp_dict */
    0,                          /* tp_descr_get */
    0,                          /* tp_descr_set */
    offsetof(PyBaseExceptionObject, dict), /* tp_dictoffset */
    BaseException_init,         /* tp_init */
    0,                          /* tp_alloc */
    BaseException_new,          /* tp_new */
    .tp_vectorcall = BaseException_vectorcall,
};
/* the CPython API expects exceptions to be (PyObject *) - both a hold-over
from the previous implementation and also allowing Python objects to be used
in the API */
PyObject *PyExc_BaseException = (PyObject *)&_PyExc_BaseException;

/* note these macros omit the last semicolon so the macro invocation may
 * include it and not look strange.
 */
#define SimpleExtendsException(EXCBASE, EXCNAME, EXCDOC) \
static PyTypeObject _PyExc_ ## EXCNAME = { \
    PyVarObject_HEAD_INIT(NULL, 0) \
    # EXCNAME, \
    sizeof(PyBaseExceptionObject), \
    0, BaseException_dealloc, 0, 0, 0, 0, 0, 0, 0, \
    0, 0, 0, 0, 0, 0, 0, \
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HAVE_GC, \
    PyDoc_STR(EXCDOC), BaseException_traverse, \
    BaseException_clear, 0, 0, 0, 0, 0, 0, 0, &_ ## EXCBASE, \
    0, 0, 0, offsetof(PyBaseExceptionObject, dict), \
    BaseException_init, 0, BaseException_new,\
}; \
PyObject *PyExc_ ## EXCNAME = (PyObject *)&_PyExc_ ## EXCNAME

#define MiddlingExtendsExceptionEx(EXCBASE, EXCNAME, PYEXCNAME, EXCSTORE, EXCDOC) \
PyTypeObject _PyExc_ ## EXCNAME = { \
    PyVarObject_HEAD_INIT(NULL, 0) \
    # PYEXCNAME, \
    sizeof(Py ## EXCSTORE ## Object), \
    0, EXCSTORE ## _dealloc, 0, 0, 0, 0, 0, 0, 0, 0, 0, \
    0, 0, 0, 0, 0, \
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HAVE_GC, \
    PyDoc_STR(EXCDOC), EXCSTORE ## _traverse, \
    EXCSTORE ## _clear, 0, 0, 0, 0, 0, 0, 0, &_ ## EXCBASE, \
    0, 0, 0, offsetof(Py ## EXCSTORE ## Object, dict), \
    EXCSTORE ## _init, 0, 0, \
};

#define MiddlingExtendsException(EXCBASE, EXCNAME, EXCSTORE, EXCDOC) \
    static MiddlingExtendsExceptionEx( \
        EXCBASE, EXCNAME, EXCNAME, EXCSTORE, EXCDOC); \
    PyObject *PyExc_ ## EXCNAME = (PyObject *)&_PyExc_ ## EXCNAME

#define ComplexExtendsException(EXCBASE, EXCNAME, EXCSTORE, EXCNEW, \
                                EXCMETHODS, EXCMEMBERS, EXCGETSET, \
                                EXCSTR, EXCDOC) \
static PyTypeObject _PyExc_ ## EXCNAME = { \
    PyVarObject_HEAD_INIT(NULL, 0) \
    # EXCNAME, \
    sizeof(Py ## EXCSTORE ## Object), 0, \
    EXCSTORE ## _dealloc, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, \
    EXCSTR, 0, 0, 0, \
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HAVE_GC, \
    PyDoc_STR(EXCDOC), EXCSTORE ## _traverse, \
    EXCSTORE ## _clear, 0, 0, 0, 0, EXCMETHODS, \
    EXCMEMBERS, EXCGETSET, &_ ## EXCBASE, \
    0, 0, 0, offsetof(Py ## EXCSTORE ## Object, dict), \
    EXCSTORE ## _init, 0, EXCNEW,\
}; \
PyObject *PyExc_ ## EXCNAME = (PyObject *)&_PyExc_ ## EXCNAME


/*
 *    Exception extends BaseException
 */
SimpleExtendsException(PyExc_BaseException, Exception,
                       "Common base class for all non-exit exceptions.");


/*
 *    TypeError extends Exception
 */
SimpleExtendsException(PyExc_Exception, TypeError,
                       "Inappropriate argument type.");


/*
 *    StopAsyncIteration extends Exception
 */
SimpleExtendsException(PyExc_Exception, StopAsyncIteration,
                       "Signal the end from iterator.__anext__().");


/*
 *    StopIteration extends Exception
 */

static PyMemberDef StopIteration_members[] = {
    {"value", _Py_T_OBJECT, offsetof(PyStopIterationObject, value), 0,
        PyDoc_STR("generator return value")},
    {NULL}  /* Sentinel */
};

static inline PyStopIterationObject *
PyStopIterationObject_CAST(PyObject *self)
{
    assert(PyObject_TypeCheck(self, (PyTypeObject *)PyExc_StopIteration));
    return (PyStopIterationObject *)self;
}

static int
StopIteration_init(PyObject *op, PyObject *args, PyObject *kwds)
{
    Py_ssize_t size = PyTuple_GET_SIZE(args);
    PyObject *value;

    if (BaseException_init(op, args, kwds) == -1)
        return -1;
    PyStopIterationObject *self = PyStopIterationObject_CAST(op);
    Py_CLEAR(self->value);
    if (size > 0)
        value = PyTuple_GET_ITEM(args, 0);
    else
        value = Py_None;
    self->value = Py_NewRef(value);
    return 0;
}

static int
StopIteration_clear(PyObject *op)
{
    PyStopIterationObject *self = PyStopIterationObject_CAST(op);
    Py_CLEAR(self->value);
    return BaseException_clear(op);
}

static void
StopIteration_dealloc(PyObject *self)
{
    PyObject_GC_UnTrack(self);
    (void)StopIteration_clear(self);
    Py_TYPE(self)->tp_free(self);
}

static int
StopIteration_traverse(PyObject *op, visitproc visit, void *arg)
{
    PyStopIterationObject *self = PyStopIterationObject_CAST(op);
    Py_VISIT(self->value);
    return BaseException_traverse(op, visit, arg);
}

ComplexExtendsException(PyExc_Exception, StopIteration, StopIteration,
                        0, 0, StopIteration_members, 0, 0,
                        "Signal the end from iterator.__next__().");


/*
 *    GeneratorExit extends BaseException
 */
SimpleExtendsException(PyExc_BaseException, GeneratorExit,
                       "Request that a generator exit.");


/*
 *    SystemExit extends BaseException
 */

static inline PySystemExitObject *
PySystemExitObject_CAST(PyObject *self)
{
    assert(PyObject_TypeCheck(self, (PyTypeObject *)PyExc_SystemExit));
    return (PySystemExitObject *)self;
}

static int
SystemExit_init(PyObject *op, PyObject *args, PyObject *kwds)
{
    Py_ssize_t size = PyTuple_GET_SIZE(args);

    if (BaseException_init(op, args, kwds) == -1)
        return -1;

    PySystemExitObject *self = PySystemExitObject_CAST(op);
    if (size == 0)
        return 0;
    if (size == 1) {
        Py_XSETREF(self->code, Py_NewRef(PyTuple_GET_ITEM(args, 0)));
    }
    else { /* size > 1 */
        Py_XSETREF(self->code, Py_NewRef(args));
    }
    return 0;
}

static int
SystemExit_clear(PyObject *op)
{
    PySystemExitObject *self = PySystemExitObject_CAST(op);
    Py_CLEAR(self->code);
    return BaseException_clear(op);
}

static void
SystemExit_dealloc(PyObject *self)
{
    _PyObject_GC_UNTRACK(self);
    (void)SystemExit_clear(self);
    Py_TYPE(self)->tp_free(self);
}

static int
SystemExit_traverse(PyObject *op, visitproc visit, void *arg)
{
    PySystemExitObject *self = PySystemExitObject_CAST(op);
    Py_VISIT(self->code);
    return BaseException_traverse(op, visit, arg);
}

static PyMemberDef SystemExit_members[] = {
    {"code", _Py_T_OBJECT, offsetof(PySystemExitObject, code), 0,
        PyDoc_STR("exception code")},
    {NULL}  /* Sentinel */
};

ComplexExtendsException(PyExc_BaseException, SystemExit, SystemExit,
                        0, 0, SystemExit_members, 0, 0,
                        "Request to exit from the interpreter.");

/*
 *    BaseExceptionGroup extends BaseException
 *    ExceptionGroup extends BaseExceptionGroup and Exception
 */


static inline PyBaseExceptionGroupObject*
PyBaseExceptionGroupObject_CAST(PyObject *exc)
{
    assert(_PyBaseExceptionGroup_Check(exc));
    return (PyBaseExceptionGroupObject *)exc;
}

static PyObject *
BaseExceptionGroup_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
    struct _Py_exc_state *state = get_exc_state();
    PyTypeObject *PyExc_ExceptionGroup =
        (PyTypeObject*)state->PyExc_ExceptionGroup;

    PyObject *message = NULL;
    PyObject *exceptions = NULL;

    if (!PyArg_ParseTuple(args,
                          "UO:BaseExceptionGroup.__new__",
                          &message,
                          &exceptions)) {
        return NULL;
    }

    if (!PySequence_Check(exceptions)) {
        PyErr_SetString(
            PyExc_TypeError,
            "second argument (exceptions) must be a sequence");
        return NULL;
    }

    exceptions = PySequence_Tuple(exceptions);
    if (!exceptions) {
        return NULL;
    }

    /* We are now holding a ref to the exceptions tuple */

    Py_ssize_t numexcs = PyTuple_GET_SIZE(exceptions);
    if (numexcs == 0) {
        PyErr_SetString(
            PyExc_ValueError,
            "second argument (exceptions) must be a non-empty sequence");
        goto error;
    }

    bool nested_base_exceptions = false;
    for (Py_ssize_t i = 0; i < numexcs; i++) {
        PyObject *exc = PyTuple_GET_ITEM(exceptions, i);
        if (!exc) {
            goto error;
        }
        if (!PyExceptionInstance_Check(exc)) {
            PyErr_Format(
                PyExc_ValueError,
                "Item %d of second argument (exceptions) is not an exception",
                i);
            goto error;
        }
        int is_nonbase_exception = PyObject_IsInstance(exc, PyExc_Exception);
        if (is_nonbase_exception < 0) {
            goto error;
        }
        else if (is_nonbase_exception == 0) {
            nested_base_exceptions = true;
        }
    }

    PyTypeObject *cls = type;
    if (cls == PyExc_ExceptionGroup) {
        if (nested_base_exceptions) {
            PyErr_SetString(PyExc_TypeError,
                "Cannot nest BaseExceptions in an ExceptionGroup");
            goto error;
        }
    }
    else if (cls == (PyTypeObject*)PyExc_BaseExceptionGroup) {
        if (!nested_base_exceptions) {
            /* All nested exceptions are Exception subclasses,
             * wrap them in an ExceptionGroup
             */
            cls = PyExc_ExceptionGroup;
        }
    }
    else {
        /* user-defined subclass */
        if (nested_base_exceptions) {
            int nonbase = PyObject_IsSubclass((PyObject*)cls, PyExc_Exception);
            if (nonbase == -1) {
                goto error;
            }
            else if (nonbase == 1) {
                PyErr_Format(PyExc_TypeError,
                    "Cannot nest BaseExceptions in '%.200s'",
                    cls->tp_name);
                goto error;
            }
        }
    }

    if (!cls) {
        /* Don't crash during interpreter shutdown
         * (PyExc_ExceptionGroup may have been cleared)
         */
        cls = (PyTypeObject*)PyExc_BaseExceptionGroup;
    }
    PyBaseExceptionGroupObject *self =
        PyBaseExceptionGroupObject_CAST(BaseException_new(cls, args, kwds));
    if (!self) {
        goto error;
    }

    self->msg = Py_NewRef(message);
    self->excs = exceptions;
    return (PyObject*)self;
error:
    Py_DECREF(exceptions);
    return NULL;
}

PyObject *
_PyExc_CreateExceptionGroup(const char *msg_str, PyObject *excs)
{