errors.c

/* Error handling */

#include "Python.h"
#include "pycore_call.h"          // _PyObject_CallNoArgs()
#include "pycore_initconfig.h"    // _PyStatus_ERR()
#include "pycore_pyerrors.h"      // _PyErr_Format()
#include "pycore_pystate.h"       // _PyThreadState_GET()
#include "pycore_structseq.h"     // _PyStructSequence_FiniBuiltin()
#include "pycore_sysmodule.h"     // _PySys_Audit()
#include "pycore_traceback.h"     // _PyTraceBack_FromFrame()

#ifdef MS_WINDOWS
#  include <windows.h>
#  include <winbase.h>
#  include <stdlib.h>             // _sys_nerr
#endif

/* Forward declarations */
static PyObject *
_PyErr_FormatV(PyThreadState *tstate, PyObject *exception,
               const char *format, va_list vargs);

void
_PyErr_SetRaisedException(PyThreadState *tstate, PyObject *exc)
{
    PyObject *old_exc = tstate->current_exception;
    tstate->current_exception = exc;
    Py_XDECREF(old_exc);
}

static PyObject*
_PyErr_CreateException(PyObject *exception_type, PyObject *value)
{
    PyObject *exc;

    if (value == NULL || value == Py_None) {
        exc = _PyObject_CallNoArgs(exception_type);
    }
    else if (PyTuple_Check(value)) {
        exc = PyObject_Call(exception_type, value, NULL);
    }
    else {
        exc = PyObject_CallOneArg(exception_type, value);
    }

    if (exc != NULL && !PyExceptionInstance_Check(exc)) {
        PyErr_Format(PyExc_TypeError,
                     "calling %R should have returned an instance of "
                     "BaseException, not %s",
                     exception_type, Py_TYPE(exc)->tp_name);
        Py_CLEAR(exc);
    }

    return exc;
}

void
_PyErr_Restore(PyThreadState *tstate, PyObject *type, PyObject *value,
               PyObject *traceback)
{
    if (type == NULL) {
        assert(value == NULL);
        assert(traceback == NULL);
        _PyErr_SetRaisedException(tstate, NULL);
        return;
    }
    assert(PyExceptionClass_Check(type));
    if (value != NULL && type == (PyObject *)Py_TYPE(value)) {
        /* Already normalized */
        assert(((PyBaseExceptionObject *)value)->traceback != Py_None);
    }
    else {
        PyObject *exc = _PyErr_CreateException(type, value);
        Py_XDECREF(value);
        if (exc == NULL) {
            Py_DECREF(type);
            Py_XDECREF(traceback);
            return;
        }
        value = exc;
    }
    assert(PyExceptionInstance_Check(value));
    if (traceback != NULL && !PyTraceBack_Check(traceback)) {
        if (traceback == Py_None) {
            Py_DECREF(Py_None);
            traceback = NULL;
        }
        else {
            PyErr_SetString(PyExc_TypeError, "traceback must be a Traceback or None");
            Py_XDECREF(value);
            Py_DECREF(type);
            Py_XDECREF(traceback);
            return;
        }
    }
    PyObject *old_traceback = ((PyBaseExceptionObject *)value)->traceback;
    ((PyBaseExceptionObject *)value)->traceback = traceback;
    Py_XDECREF(old_traceback);
    _PyErr_SetRaisedException(tstate, value);
    Py_DECREF(type);
}

void
PyErr_Restore(PyObject *type, PyObject *value, PyObject *traceback)
{
    PyThreadState *tstate = _PyThreadState_GET();
    _PyErr_Restore(tstate, type, value, traceback);
}

void
PyErr_SetRaisedException(PyObject *exc)
{
    PyThreadState *tstate = _PyThreadState_GET();
    _PyErr_SetRaisedException(tstate, exc);
}

_PyErr_StackItem *
_PyErr_GetTopmostException(PyThreadState *tstate)
{
    _PyErr_StackItem *exc_info = tstate->exc_info;
    assert(exc_info);

    while (exc_info->exc_value == NULL && exc_info->previous_item != NULL)
    {
        exc_info = exc_info->previous_item;
    }
    assert(!Py_IsNone(exc_info->exc_value));
    return exc_info;
}

static PyObject *
get_normalization_failure_note(PyThreadState *tstate, PyObject *exception, PyObject *value)
{
    PyObject *args = PyObject_Repr(value);
    if (args == NULL) {
        _PyErr_Clear(tstate);
        args = PyUnicode_FromFormat("<unknown>");
    }
    PyObject *note;
    const char *tpname = ((PyTypeObject*)exception)->tp_name;
    if (args == NULL) {
        _PyErr_Clear(tstate);
        note = PyUnicode_FromFormat("Normalization failed: type=%s", tpname);
    }
    else {
        note = PyUnicode_FromFormat("Normalization failed: type=%s args=%S",
                                    tpname, args);
        Py_DECREF(args);
    }
    return note;
}

void
_PyErr_SetObject(PyThreadState *tstate, PyObject *exception, PyObject *value)
{
    PyObject *exc_value;
    PyObject *tb = NULL;

    if (exception != NULL &&
        !PyExceptionClass_Check(exception)) {
        _PyErr_Format(tstate, PyExc_SystemError,
                      "_PyErr_SetObject: "
                      "exception %R is not a BaseException subclass",
                      exception);
        return;
    }
    /* Normalize the exception */
    int is_subclass = 0;
    if (value != NULL && PyExceptionInstance_Check(value)) {
        is_subclass = PyObject_IsSubclass((PyObject *)Py_TYPE(value), exception);
        if (is_subclass < 0) {
            return;
        }
    }
    Py_XINCREF(value);
    if (!is_subclass) {
        /* We must normalize the value right now */

        /* Issue #23571: functions must not be called with an
            exception set */
        _PyErr_Clear(tstate);

        PyObject *fixed_value = _PyErr_CreateException(exception, value);
        if (fixed_value == NULL) {
            PyObject *exc = _PyErr_GetRaisedException(tstate);
            assert(PyExceptionInstance_Check(exc));

            PyObject *note = get_normalization_failure_note(tstate, exception, value);
            Py_XDECREF(value);
            if (note != NULL) {
                /* ignore errors in _PyException_AddNote - they will be overwritten below */
                _PyException_AddNote(exc, note);
                Py_DECREF(note);
            }
            _PyErr_SetRaisedException(tstate, exc);
            return;
        }
        Py_XSETREF(value, fixed_value);
    }

    exc_value = _PyErr_GetTopmostException(tstate)->exc_value;
    if (exc_value != NULL && exc_value != Py_None) {
        /* Implicit exception chaining */
        Py_INCREF(exc_value);
        /* Avoid creating new reference cycles through the
           context chain, while taking care not to hang on
           pre-existing ones.
           This is O(chain length) but context chains are
           usually very short. Sensitive readers may try
           to inline the call to PyException_GetContext. */
        if (exc_value != value) {
            PyObject *o = exc_value, *context;
            PyObject *slow_o = o;  /* Floyd's cycle detection algo */
            int slow_update_toggle = 0;
            while ((context = PyException_GetContext(o))) {
                Py_DECREF(context);
                if (context == value) {
                    PyException_SetContext(o, NULL);
                    break;
                }
                o = context;
                if (o == slow_o) {
                    /* pre-existing cycle - all exceptions on the
                       path were visited and checked.  */
                    break;
                }
                if (slow_update_toggle) {
                    slow_o = PyException_GetContext(slow_o);
                    Py_DECREF(slow_o);
                }
                slow_update_toggle = !slow_update_toggle;
            }
            PyException_SetContext(value, exc_value);
        }
        else {
            Py_DECREF(exc_value);
        }
    }
    assert(value != NULL);
    if (PyExceptionInstance_Check(value))
        tb = PyException_GetTraceback(value);
    _PyErr_Restore(tstate, Py_NewRef(Py_TYPE(value)), value, tb);
}

void
PyErr_SetObject(PyObject *exception, PyObject *value)
{
    PyThreadState *tstate = _PyThreadState_GET();
    _PyErr_SetObject(tstate, exception, value);
}

/* Set a key error with the specified argument, wrapping it in a
 * tuple automatically so that tuple keys are not unpacked as the
 * exception arguments. */
void
_PyErr_SetKeyError(PyObject *arg)
{
    PyThreadState *tstate = _PyThreadState_GET();
    PyObject *tup = PyTuple_Pack(1, arg);
    if (!tup) {
        /* caller will expect error to be set anyway */
        return;
    }
    _PyErr_SetObject(tstate, PyExc_KeyError, tup);
    Py_DECREF(tup);
}

void
_PyErr_SetNone(PyThreadState *tstate, PyObject *exception)
{
    _PyErr_SetObject(tstate, exception, (PyObject *)NULL);
}


void
PyErr_SetNone(PyObject *exception)
{
    PyThreadState *tstate = _PyThreadState_GET();
    _PyErr_SetNone(tstate, exception);
}


void
_PyErr_SetString(PyThreadState *tstate, PyObject *exception,
                 const char *string)
{
    PyObject *value = PyUnicode_FromString(string);
    if (value != NULL) {
        _PyErr_SetObject(tstate, exception, value);
        Py_DECREF(value);
    }
}

void
PyErr_SetString(PyObject *exception, const char *string)
{
    PyThreadState *tstate = _PyThreadState_GET();
    _PyErr_SetString(tstate, exception, string);
}

void
_PyErr_SetLocaleString(PyObject *exception, const char *string)
{
    PyObject *value = PyUnicode_DecodeLocale(string, "surrogateescape");
    if (value != NULL) {
        PyErr_SetObject(exception, value);
        Py_DECREF(value);
    }
}

PyObject* _Py_HOT_FUNCTION
PyErr_Occurred(void)
{
    /* The caller must hold the GIL. */
    assert(PyGILState_Check());

    PyThreadState *tstate = _PyThreadState_GET();
    return _PyErr_Occurred(tstate);
}


int
PyErr_GivenExceptionMatches(PyObject *err, PyObject *exc)
{
    if (err == NULL || exc == NULL) {
        /* maybe caused by "import exceptions" that failed early on */
        return 0;
    }
    if (PyTuple_Check(exc)) {
        Py_ssize_t i, n;
        n = PyTuple_Size(exc);
        for (i = 0; i < n; i++) {
            /* Test recursively */
             if (PyErr_GivenExceptionMatches(
                 err, PyTuple_GET_ITEM(exc, i)))
             {
                 return 1;
             }
        }
        return 0;
    }
    /* err might be an instance, so check its class. */
    if (PyExceptionInstance_Check(err))
        err = PyExceptionInstance_Class(err);

    if (PyExceptionClass_Check(err) && PyExceptionClass_Check(exc)) {
        return PyType_IsSubtype((PyTypeObject *)err, (PyTypeObject *)exc);
    }

    return err == exc;
}


int
_PyErr_ExceptionMatches(PyThreadState *tstate, PyObject *exc)
{
    return PyErr_GivenExceptionMatches(_PyErr_Occurred(tstate), exc);
}


int
PyErr_ExceptionMatches(PyObject *exc)
{
    PyThreadState *tstate = _PyThreadState_GET();
    return _PyErr_ExceptionMatches(tstate, exc);
}


#ifndef Py_NORMALIZE_RECURSION_LIMIT
#define Py_NORMALIZE_RECURSION_LIMIT 32
#endif

/* Used in many places to normalize a raised exception, including in
   eval_code2(), do_raise(), and PyErr_Print()

   XXX: should PyErr_NormalizeException() also call
            PyException_SetTraceback() with the resulting value and tb?
*/
void
_PyErr_NormalizeException(PyThreadState *tstate, PyObject **exc,
                          PyObject **val, PyObject **tb)
{
    int recursion_depth = 0;
    tstate->recursion_headroom++;
    PyObject *type, *value, *initial_tb;

  restart:
    type = *exc;
    if (type == NULL) {
        /* There was no exception, so nothing to do. */
        tstate->recursion_headroom--;
        return;
    }

    value = *val;
    /* If PyErr_SetNone() was used, the value will have been actually
       set to NULL.
    */
    if (!value) {
        value = Py_NewRef(Py_None);
    }

    /* Normalize the exception so that if the type is a class, the
       value will be an instance.
    */
    if (PyExceptionClass_Check(type)) {
        PyObject *inclass = NULL;
        int is_subclass = 0;

        if (PyExceptionInstance_Check(value)) {
            inclass = PyExceptionInstance_Class(value);
            is_subclass = PyObject_IsSubclass(inclass, type);
            if (is_subclass < 0) {
                goto error;
            }
        }

        /* If the value was not an instance, or is not an instance
           whose class is (or is derived from) type, then use the
           value as an argument to instantiation of the type
           class.
        */
        if (!is_subclass) {
            PyObject *fixed_value = _PyErr_CreateException(type, value);
            if (fixed_value == NULL) {
                goto error;
            }
            Py_SETREF(value, fixed_value);
        }
        /* If the class of the instance doesn't exactly match the
           class of the type, believe the instance.
        */
        else if (inclass != type) {
            Py_SETREF(type, Py_NewRef(inclass));
        }
    }
    *exc = type;
    *val = value;
    tstate->recursion_headroom--;
    return;

  error:
    Py_DECREF(type);
    Py_DECREF(value);
    recursion_depth++;
    if (recursion_depth == Py_NORMALIZE_RECURSION_LIMIT) {
        _PyErr_SetString(tstate, PyExc_RecursionError,
                         "maximum recursion depth exceeded "
                         "while normalizing an exception");
    }
    /* If the new exception doesn't set a traceback and the old
       exception had a traceback, use the old traceback for the
       new exception.  It's better than nothing.
    */
    initial_tb = *tb;
    _PyErr_Fetch(tstate, exc, val, tb);
    assert(*exc != NULL);
    if (initial_tb != NULL) {
        if (*tb == NULL)
            *tb = initial_tb;
        else
            Py_DECREF(initial_tb);
    }
    /* Abort when Py_NORMALIZE_RECURSION_LIMIT has been exceeded, and the
       corresponding RecursionError could not be normalized, and the
       MemoryError raised when normalize this RecursionError could not be
       normalized. */
    if (recursion_depth >= Py_NORMALIZE_RECURSION_LIMIT + 2) {
        if (PyErr_GivenExceptionMatches(*exc, PyExc_MemoryError)) {
            Py_FatalError("Cannot recover from MemoryErrors "
                          "while normalizing exceptions.");
        }
        else {
            Py_FatalError("Cannot recover from the recursive normalization "
                          "of an exception.");
        }
    }
    goto restart;
}


void
PyErr_NormalizeException(PyObject **exc, PyObject **val, PyObject **tb)
{
    PyThreadState *tstate = _PyThreadState_GET();
    _PyErr_NormalizeException(tstate, exc, val, tb);
}


PyObject *
_PyErr_GetRaisedException(PyThreadState *tstate) {
    PyObject *exc = tstate->current_exception;
    tstate->current_exception = NULL;
    return exc;
}

PyObject *
PyErr_GetRaisedException(void)
{
    PyThreadState *tstate = _PyThreadState_GET();
    return _PyErr_GetRaisedException(tstate);
}

void
_PyErr_Fetch(PyThreadState *tstate, PyObject **p_type, PyObject **p_value,
             PyObject **p_traceback)
{
    PyObject *exc = _PyErr_GetRaisedException(tstate);
    *p_value = exc;
    if (exc == NULL) {
        *p_type = NULL;
        *p_traceback = NULL;
    }
    else {
        *p_type = Py_NewRef(Py_TYPE(exc));
        *p_traceback = Py_XNewRef(((PyBaseExceptionObject *)exc)->traceback);
    }
}


void
PyErr_Fetch(PyObject **p_type, PyObject **p_value, PyObject **p_traceback)
{
    PyThreadState *tstate = _PyThreadState_GET();
    _PyErr_Fetch(tstate, p_type, p_value, p_traceback);
}


void
_PyErr_Clear(PyThreadState *tstate)
{
    _PyErr_Restore(tstate, NULL, NULL, NULL);
}


void
PyErr_Clear(void)
{
    PyThreadState *tstate = _PyThreadState_GET();
    _PyErr_Clear(tstate);
}

static PyObject*
get_exc_type(PyObject *exc_value)  /* returns a borrowed ref */
{
    if (exc_value == NULL || exc_value == Py_None) {
        return Py_None;
    }
    else {
        assert(PyExceptionInstance_Check(exc_value));
        PyObject *type = PyExceptionInstance_Class(exc_value);
        assert(type != NULL);
        return type;
    }
}

static PyObject*
get_exc_traceback(PyObject *exc_value)  /* returns a borrowed ref */
{
    if (exc_value == NULL || exc_value == Py_None) {
        return Py_None;
    }
    else {
        assert(PyExceptionInstance_Check(exc_value));
        PyObject *tb = PyException_GetTraceback(exc_value);
        Py_XDECREF(tb);
        return tb ? tb : Py_None;
    }
}

void
_PyErr_GetExcInfo(PyThreadState *tstate,
                  PyObject **p_type, PyObject **p_value, PyObject **p_traceback)
{
    _PyErr_StackItem *exc_info = _PyErr_GetTopmostException(tstate);

    *p_type = Py_XNewRef(get_exc_type(exc_info->exc_value));
    *p_value = Py_XNewRef(exc_info->exc_value);
    *p_traceback = Py_XNewRef(get_exc_traceback(exc_info->exc_value));
}

PyObject*
_PyErr_GetHandledException(PyThreadState *tstate)
{
    _PyErr_StackItem *exc_info = _PyErr_GetTopmostException(tstate);
    PyObject *exc = exc_info->exc_value;
    if (exc == NULL || exc == Py_None) {
        return NULL;
    }
    return Py_NewRef(exc);
}

PyObject*
PyErr_GetHandledException(void)
{
    PyThreadState *tstate = _PyThreadState_GET();
    return _PyErr_GetHandledException(tstate);
}

void
_PyErr_SetHandledException(PyThreadState *tstate, PyObject *exc)
{
    Py_XSETREF(tstate->exc_info->exc_value, Py_XNewRef(exc == Py_None ? NULL : exc));
}

void
PyErr_SetHandledException(PyObject *exc)
{
    PyThreadState *tstate = _PyThreadState_GET();
    _PyErr_SetHandledException(tstate, exc);
}

void
PyErr_GetExcInfo(PyObject **p_type, PyObject **p_value, PyObject **p_traceback)
{
    PyThreadState *tstate = _PyThreadState_GET();
    _PyErr_GetExcInfo(tstate, p_type, p_value, p_traceback);
}

void
PyErr_SetExcInfo(PyObject *type, PyObject *value, PyObject *traceback)
{
    PyErr_SetHandledException(value);
    Py_XDECREF(value);
    /* These args are no longer used, but we still need to steal a ref */
    Py_XDECREF(type);
    Py_XDECREF(traceback);
}


PyObject*
_PyErr_StackItemToExcInfoTuple(_PyErr_StackItem *err_info)
{
    PyObject *exc_value = err_info->exc_value;

    assert(exc_value == NULL ||
           exc_value == Py_None ||
           PyExceptionInstance_Check(exc_value));

    PyObject *exc_type = get_exc_type(exc_value);
    PyObject *exc_traceback = get_exc_traceback(exc_value);

    return PyTuple_Pack(
        3,
        exc_type ? exc_type : Py_None,
        exc_value ? exc_value : Py_None,
        exc_traceback ? exc_traceback : Py_None);
}


/* Like PyErr_Restore(), but if an exception is already set,
   set the context associated with it.

   The caller is responsible for ensuring that this call won't create
   any cycles in the exception context chain. */
void
_PyErr_ChainExceptions(PyObject *typ, PyObject *val, PyObject *tb)
{
    if (typ == NULL)
        return;

    PyThreadState *tstate = _PyThreadState_GET();

    if (!PyExceptionClass_Check(typ)) {
        _PyErr_Format(tstate, PyExc_SystemError,
                      "_PyErr_ChainExceptions: "
                      "exception %R is not a BaseException subclass",
                      typ);
        return;
    }

    if (_PyErr_Occurred(tstate)) {
        _PyErr_NormalizeException(tstate, &typ, &val, &tb);
        if (tb != NULL) {
            PyException_SetTraceback(val, tb);
            Py_DECREF(tb);
        }
        Py_DECREF(typ);
        PyObject *exc2 = _PyErr_GetRaisedException(tstate);
        PyException_SetContext(exc2, val);
        _PyErr_SetRaisedException(tstate, exc2);
    }
    else {
        _PyErr_Restore(tstate, typ, val, tb);
    }
}

/* Like PyErr_SetRaisedException(), but if an exception is already set,
   set the context associated with it.

   The caller is responsible for ensuring that this call won't create
   any cycles in the exception context chain. */
void
_PyErr_ChainExceptions1(PyObject *exc)
{
    if (exc == NULL) {
        return;
    }
    PyThreadState *tstate = _PyThreadState_GET();
    if (_PyErr_Occurred(tstate)) {
        PyObject *exc2 = _PyErr_GetRaisedException(tstate);
        PyException_SetContext(exc2, exc);
        _PyErr_SetRaisedException(tstate, exc2);
    }
    else {
        _PyErr_SetRaisedException(tstate, exc);
    }
}

/* If the current thread is handling an exception (exc_info is ), set this
   exception as the context of the current raised exception.

   This function can only be called when _PyErr_Occurred() is true.
   Also, this function won't create any cycles in the exception context
   chain to the extent that _PyErr_SetObject ensures this. */
void
_PyErr_ChainStackItem(void)
{
    PyThreadState *tstate = _PyThreadState_GET();
    assert(_PyErr_Occurred(tstate));

    _PyErr_StackItem *exc_info = tstate->exc_info;
    if (exc_info->exc_value == NULL || exc_info->exc_value == Py_None) {
        return;
    }

    PyObject *exc = _PyErr_GetRaisedException(tstate);

    /* _PyErr_SetObject sets the context from PyThreadState. */
    _PyErr_SetObject(tstate, (PyObject *) Py_TYPE(exc), exc);
    Py_DECREF(exc);  // since _PyErr_Occurred was true
}

static PyObject *
_PyErr_FormatVFromCause(PyThreadState *tstate, PyObject *exception,
                        const char *format, va_list vargs)
{
    assert(_PyErr_Occurred(tstate));
    PyObject *exc = _PyErr_GetRaisedException(tstate);
    assert(!_PyErr_Occurred(tstate));
    _PyErr_FormatV(tstate, exception, format, vargs);
    PyObject *exc2 = _PyErr_GetRaisedException(tstate);
    PyException_SetCause(exc2, Py_NewRef(exc));
    PyException_SetContext(exc2, Py_NewRef(exc));
    Py_DECREF(exc);
    _PyErr_SetRaisedException(tstate, exc2);
    return NULL;
}

PyObject *
_PyErr_FormatFromCauseTstate(PyThreadState *tstate, PyObject *exception,
                             const char *format, ...)
{
    va_list vargs;
    va_start(vargs, format);
    _PyErr_FormatVFromCause(tstate, exception, format, vargs);
    va_end(vargs);
    return NULL;
}

PyObject *
_PyErr_FormatFromCause(PyObject *exception, const char *format, ...)
{
    PyThreadState *tstate = _PyThreadState_GET();
    va_list vargs;
    va_start(vargs, format);
    _PyErr_FormatVFromCause(tstate, exception, format, vargs);
    va_end(vargs);
    return NULL;
}

/* Convenience functions to set a type error exception and return 0 */

int
PyErr_BadArgument(void)
{
    PyThreadState *tstate = _PyThreadState_GET();
    _PyErr_SetString(tstate, PyExc_TypeError,
                     "bad argument type for built-in operation");
    return 0;
}

PyObject *
PyErr_NoMemory(void)
{
    PyThreadState *tstate = _PyThreadState_GET();
    return _PyErr_NoMemory(tstate);
}

PyObject *
PyErr_SetFromErrnoWithFilenameObject(PyObject *exc, PyObject *filenameObject)
{
    return PyErr_SetFromErrnoWithFilenameObjects(exc, filenameObject, NULL);
}

PyObject *
PyErr_SetFromErrnoWithFilenameObjects(PyObject *exc, PyObject *filenameObject, PyObject *filenameObject2)
{
    PyThreadState *tstate = _PyThreadState_GET();
    PyObject *message;
    PyObject *v, *args;
    int i = errno;
#ifdef MS_WINDOWS
    WCHAR *s_buf = NULL;
#endif /* Unix/Windows */

#ifdef EINTR
    if (i == EINTR && PyErr_CheckSignals())
        return NULL;
#endif

#ifndef MS_WINDOWS
    if (i != 0) {
        const char *s = strerror(i);
        message = PyUnicode_DecodeLocale(s, "surrogateescape");
    }
    else {
        /* Sometimes errno didn't get set */
        message = PyUnicode_FromString("Error");
    }
#else
    if (i == 0)
        message = PyUnicode_FromString("Error"); /* Sometimes errno didn't get set */
    else
    {
        /* Note that the Win32 errors do not lineup with the
           errno error.  So if the error is in the MSVC error
           table, we use it, otherwise we assume it really _is_
           a Win32 error code
        */
        if (i > 0 && i < _sys_nerr) {
            message = PyUnicode_FromString(_sys_errlist[i]);
        }
        else {
            int len = FormatMessageW(
                FORMAT_MESSAGE_ALLOCATE_BUFFER |
                FORMAT_MESSAGE_FROM_SYSTEM |
                FORMAT_MESSAGE_IGNORE_INSERTS,
                NULL,                   /* no message source */
                i,
                MAKELANGID(LANG_NEUTRAL,
                           SUBLANG_DEFAULT),
                           /* Default language */
                (LPWSTR) &s_buf,
                0,                      /* size not used */
                NULL);                  /* no args */
            if (len==0) {
                /* Only ever seen this in out-of-mem
                   situations */
                s_buf = NULL;
                message = PyUnicode_FromFormat("Windows Error 0x%x", i);
            } else {
                /* remove trailing cr/lf and dots */
                while (len > 0 && (s_buf[len-1] <= L' ' || s_buf[len-1] == L'.'))
                    s_buf[--len] = L'\0';
                message = PyUnicode_FromWideChar(s_buf, len);
            }
        }
    }
#endif /* Unix/Windows */

    if (message == NULL)
    {
#ifdef MS_WINDOWS
        LocalFree(s_buf);
#endif
        return NULL;
    }

    if (filenameObject != NULL) {
        if (filenameObject2 != NULL)
            args = Py_BuildValue("(iOOiO)", i, message, filenameObject, 0, filenameObject2);
        else
            args = Py_BuildValue("(iOO)", i, message, filenameObject);
    } else {
        assert(filenameObject2 == NULL);
        args = Py_BuildValue("(iO)", i, message);
    }
    Py_DECREF(message);

    if (args != NULL) {
        v = PyObject_Call(exc, args, NULL);
        Py_DECREF(args);
        if (v != NULL) {
            _PyErr_SetObject(tstate, (PyObject *) Py_TYPE(v), v);
            Py_DECREF(v);
        }
    }
#ifdef MS_WINDOWS
    LocalFree(s_buf);
#endif
    return NULL;
}

PyObject *
PyErr_SetFromErrnoWithFilename(PyObject *exc, const char *filename)
{
    PyObject *name = NULL;
    if (filename) {
        int i = errno;
        name = PyUnicode_DecodeFSDefault(filename);
        if (name == NULL) {
            return NULL;
        }
        errno = i;
    }
    PyObject *result = PyErr_SetFromErrnoWithFilenameObjects(exc, name, NULL);
    Py_XDECREF(name);
    return result;
}

PyObject *
PyErr_SetFromErrno(PyObject *exc)
{
    return PyErr_SetFromErrnoWithFilenameObjects(exc, NULL, NULL);
}

#ifdef MS_WINDOWS
/* Windows specific error code handling */
PyObject *PyErr_SetExcFromWindowsErrWithFilenameObject(
    PyObject *exc,
    int ierr,
    PyObject *filenameObject)
{
    return PyErr_SetExcFromWindowsErrWithFilenameObjects(exc, ierr,
        filenameObject, NULL);
}

PyObject *PyErr_SetExcFromWindowsErrWithFilenameObjects(
    PyObject *exc,
    int ierr,
    PyObject *filenameObject,
    PyObject *filenameObject2)
{
    PyThreadState *tstate = _PyThreadState_GET();
    int len;
    WCHAR *s_buf = NULL; /* Free via LocalFree */
    PyObject *message;
    PyObject *args, *v;

    DWORD err = (DWORD)ierr;
    if (err==0) {
        err = GetLastError();
    }

    len = FormatMessageW(
        /* Error API error */
        FORMAT_MESSAGE_ALLOCATE_BUFFER |
        FORMAT_MESSAGE_FROM_SYSTEM |
        FORMAT_MESSAGE_IGNORE_INSERTS,
        NULL,           /* no message source */
        err,
        MAKELANGID(LANG_NEUTRAL,
        SUBLANG_DEFAULT), /* Default language */
        (LPWSTR) &s_buf,
        0,              /* size not used */
        NULL);          /* no args */
    if (len==0) {
        /* Only seen this in out of mem situations */
        message = PyUnicode_FromFormat("Windows Error 0x%x", err);
        s_buf = NULL;
    } else {
        /* remove trailing cr/lf and dots */
        while (len > 0 && (s_buf[len-1] <= L' ' || s_buf[len-1] == L'.'))
            s_buf[--len] = L'\0';
        message = PyUnicode_FromWideChar(s_buf, len);
    }

    if (message == NULL)
    {
        LocalFree(s_buf);
        return NULL;
    }

    if (filenameObject == NULL) {
        assert(filenameObject2 == NULL);
        filenameObject = filenameObject2 = Py_None;
    }
    else if (filenameObject2 == NULL)
        filenameObject2 = Py_None;
    /* This is the constructor signature for OSError.
       The POSIX translation will be figured out by the constructor. */
    args = Py_BuildValue("(iOOiO)", 0, message, filenameObject, err, filenameObject2);
    Py_DECREF(message);

    if (args != NULL) {
        v = PyObject_Call(exc, args, NULL);
        Py_DECREF(args);
        if (v != NULL) {
            _PyErr_SetObject(tstate, (PyObject *) Py_TYPE(v), v);
            Py_DECREF(v);
        }
    }
    LocalFree(s_buf);
    return NULL;
}

PyObject *PyErr_SetExcFromWindowsErrWithFilename(
    PyObject *exc,