cpython/Python/errors.c

/* Error handling */

#include "Python.h"

#ifndef __STDC__
#ifndef MS_WINDOWS
extern char *strerror(int);
#endif
#endif

#ifdef MS_WINDOWS
#include <windows.h>
#include <winbase.h>
#endif

#include <ctype.h>

#ifdef __cplusplus
extern "C" {
#endif


void
PyErr_Restore(PyObject *type, PyObject *value, PyObject *traceback)
{
    PyThreadState *tstate = PyThreadState_GET();
    PyObject *oldtype, *oldvalue, *oldtraceback;

    if (traceback != NULL && !PyTraceBack_Check(traceback)) {
        /* XXX Should never happen -- fatal error instead? */
        /* Well, it could be None. */
        Py_DECREF(traceback);
        traceback = NULL;
    }

    /* Save these in locals to safeguard against recursive
       invocation through Py_XDECREF */
    oldtype = tstate->curexc_type;
    oldvalue = tstate->curexc_value;
    oldtraceback = tstate->curexc_traceback;

    tstate->curexc_type = type;
    tstate->curexc_value = value;
    tstate->curexc_traceback = traceback;

    Py_XDECREF(oldtype);
    Py_XDECREF(oldvalue);
    Py_XDECREF(oldtraceback);
}

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

    if (exception != NULL &&
        !PyExceptionClass_Check(exception)) {
        PyErr_Format(PyExc_SystemError,
                     "exception %R not a BaseException subclass",
                     exception);
        return;
    }
    Py_XINCREF(value);
    exc_value = tstate->exc_value;
    if (exc_value != NULL && exc_value != Py_None) {
        /* Implicit exception chaining */
        Py_INCREF(exc_value);
        if (value == NULL || !PyExceptionInstance_Check(value)) {
            /* We must normalize the value right now */
            PyObject *args, *fixed_value;
            if (value == NULL || value == Py_None)
                args = PyTuple_New(0);
            else if (PyTuple_Check(value)) {
                Py_INCREF(value);
                args = value;
            }
            else
                args = PyTuple_Pack(1, value);
            fixed_value = args ?
                PyEval_CallObject(exception, args) : NULL;
            Py_XDECREF(args);
            Py_XDECREF(value);
            if (fixed_value == NULL)
                return;
            value = fixed_value;
        }
        /* Avoid reference cycles through the context chain.
           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;
            while ((context = PyException_GetContext(o))) {
                Py_DECREF(context);
                if (context == value) {
                    PyException_SetContext(o, NULL);
                    break;
                }
                o = context;
            }
            PyException_SetContext(value, exc_value);
        } else {
            Py_DECREF(exc_value);
        }
    }
    if (value != NULL && PyExceptionInstance_Check(value))
        tb = PyException_GetTraceback(value);
    Py_XINCREF(exception);
    PyErr_Restore(exception, value, tb);
}

void
PyErr_SetNone(PyObject *exception)
{
    PyErr_SetObject(exception, (PyObject *)NULL);
}

void
PyErr_SetString(PyObject *exception, const char *string)
{
    PyObject *value = PyUnicode_FromString(string);
    PyErr_SetObject(exception, value);
    Py_XDECREF(value);
}


PyObject *
PyErr_Occurred(void)
{
    /* If there is no thread state, PyThreadState_GET calls
       Py_FatalError, which calls PyErr_Occurred.  To avoid the
       resulting infinite loop, we inline PyThreadState_GET here and
       treat no thread as no error. */
    PyThreadState *tstate =
        ((PyThreadState*)_Py_atomic_load_relaxed(&_PyThreadState_Current));

    return tstate == NULL ? NULL : tstate->curexc_type;
}


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)) {
        int res = 0;
        PyObject *exception, *value, *tb;
        PyErr_Fetch(&exception, &value, &tb);
        /* PyObject_IsSubclass() can recurse and therefore is
           not safe (see test_bad_getattr in test.pickletester). */
        res = PyType_IsSubtype((PyTypeObject *)err, (PyTypeObject *)exc);
        /* This function must not fail, so print the error here */
        if (res == -1) {
            PyErr_WriteUnraisable(err);
            res = 0;
        }
        PyErr_Restore(exception, value, tb);
        return res;
    }

    return err == exc;
}


int
PyErr_ExceptionMatches(PyObject *exc)
{
    return PyErr_GivenExceptionMatches(PyErr_Occurred(), exc);
}


/* 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(PyObject **exc, PyObject **val, PyObject **tb)
{
    PyObject *type = *exc;
    PyObject *value = *val;
    PyObject *inclass = NULL;
    PyObject *initial_tb = NULL;
    PyThreadState *tstate = NULL;

    if (type == NULL) {
        /* There was no exception, so nothing to do. */
        return;
    }

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

    if (PyExceptionInstance_Check(value))
        inclass = PyExceptionInstance_Class(value);

    /* Normalize the exception so that if the type is a class, the
       value will be an instance.
    */
    if (PyExceptionClass_Check(type)) {
        /* 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 (!inclass || !PyObject_IsSubclass(inclass, type)) {
            PyObject *args, *res;

            if (value == Py_None)
                args = PyTuple_New(0);
            else if (PyTuple_Check(value)) {
                Py_INCREF(value);
                args = value;
            }
            else
                args = PyTuple_Pack(1, value);

            if (args == NULL)
                goto finally;
            res = PyEval_CallObject(type, args);
            Py_DECREF(args);
            if (res == NULL)
                goto finally;
            Py_DECREF(value);
            value = res;
        }
        /* if the class of the instance doesn't exactly match the
           class of the type, believe the instance
        */
        else if (inclass != type) {
            Py_DECREF(type);
            type = inclass;
            Py_INCREF(type);
        }
    }
    *exc = type;
    *val = value;
    return;
finally:
    Py_DECREF(type);
    Py_DECREF(value);
    /* 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(exc, val, tb);
    if (initial_tb != NULL) {
        if (*tb == NULL)
            *tb = initial_tb;
        else
            Py_DECREF(initial_tb);
    }
    /* normalize recursively */
    tstate = PyThreadState_GET();
    if (++tstate->recursion_depth > Py_GetRecursionLimit()) {
        --tstate->recursion_depth;
        /* throw away the old exception... */
        Py_DECREF(*exc);
        Py_DECREF(*val);
        /* ... and use the recursion error instead */
        *exc = PyExc_RuntimeError;
        *val = PyExc_RecursionErrorInst;
        Py_INCREF(*exc);
        Py_INCREF(*val);
        /* just keeping the old traceback */
        return;
    }
    PyErr_NormalizeException(exc, val, tb);
    --tstate->recursion_depth;
}


void
PyErr_Fetch(PyObject **p_type, PyObject **p_value, PyObject **p_traceback)
{
    PyThreadState *tstate = PyThreadState_GET();

    *p_type = tstate->curexc_type;
    *p_value = tstate->curexc_value;
    *p_traceback = tstate->curexc_traceback;

    tstate->curexc_type = NULL;
    tstate->curexc_value = NULL;
    tstate->curexc_traceback = NULL;
}

void
PyErr_Clear(void)
{
    PyErr_Restore(NULL, NULL, NULL);
}

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

int
PyErr_BadArgument(void)
{
    PyErr_SetString(PyExc_TypeError,
                    "bad argument type for built-in operation");
    return 0;
}

PyObject *
PyErr_NoMemory(void)
{
    if (PyErr_ExceptionMatches(PyExc_MemoryError))
        /* already current */
        return NULL;

    /* raise the pre-allocated instance if it still exists */
    if (PyExc_MemoryErrorInst)
    {
        /* Clear the previous traceback, otherwise it will be appended
         * to the current one.
         *
         * The following statement is not likely to raise any error;
         * if it does, we simply discard it.
         */
        PyException_SetTraceback(PyExc_MemoryErrorInst, Py_None);

        PyErr_SetObject(PyExc_MemoryError, PyExc_MemoryErrorInst);
    }
    else
        /* this will probably fail since there's no memory and hee,
           hee, we have to instantiate this class
        */
        PyErr_SetNone(PyExc_MemoryError);

    return NULL;
}

PyObject *
PyErr_SetFromErrnoWithFilenameObject(PyObject *exc, PyObject *filenameObject)
{
    PyObject *message;
    PyObject *v;
    int i = errno;
#ifndef MS_WINDOWS
    char *s;
#else
    WCHAR *s_buf = NULL;
#endif /* Unix/Windows */

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

#ifndef MS_WINDOWS
    if (i == 0)
        s = "Error"; /* Sometimes errno didn't get set */
    else
        s = strerror(i);
    message = PyUnicode_DecodeUTF8(s, strlen(s), "ignore");
#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_FromUnicode(s_buf, len);
            }
        }
    }
#endif /* Unix/Windows */

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

    if (filenameObject != NULL)
        v = Py_BuildValue("(iOO)", i, message, filenameObject);
    else
        v = Py_BuildValue("(iO)", i, message);
    Py_DECREF(message);

    if (v != NULL) {
        PyErr_SetObject(exc, v);
        Py_DECREF(v);
    }
#ifdef MS_WINDOWS
    LocalFree(s_buf);
#endif
    return NULL;
}


PyObject *
PyErr_SetFromErrnoWithFilename(PyObject *exc, const char *filename)
{
    PyObject *name = filename ? PyUnicode_DecodeFSDefault(filename) : NULL;
    PyObject *result = PyErr_SetFromErrnoWithFilenameObject(exc, name);
    Py_XDECREF(name);
    return result;
}

#ifdef MS_WINDOWS
PyObject *
PyErr_SetFromErrnoWithUnicodeFilename(PyObject *exc, const Py_UNICODE *filename)
{
    PyObject *name = filename ?
                     PyUnicode_FromUnicode(filename, wcslen(filename)) :
             NULL;
    PyObject *result = PyErr_SetFromErrnoWithFilenameObject(exc, name);
    Py_XDECREF(name);
    return result;
}
#endif /* MS_WINDOWS */

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

#ifdef MS_WINDOWS
/* Windows specific error code handling */
PyObject *PyErr_SetExcFromWindowsErrWithFilenameObject(
    PyObject *exc,
    int ierr,
    PyObject *filenameObject)
{
    int len;
    WCHAR *s_buf = NULL; /* Free via LocalFree */
    PyObject *message;
    PyObject *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_FromUnicode(s_buf, len);
    }

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

    if (filenameObject != NULL)
        v = Py_BuildValue("(iOO)", err, message, filenameObject);
    else
        v = Py_BuildValue("(iO)", err, message);
    Py_DECREF(message);

    if (v != NULL) {
        PyErr_SetObject(exc, v);
        Py_DECREF(v);
    }
    LocalFree(s_buf);
    return NULL;
}

PyObject *PyErr_SetExcFromWindowsErrWithFilename(
    PyObject *exc,
    int ierr,
    const char *filename)
{
    PyObject *name = filename ? PyUnicode_FromString(filename) : NULL;
    PyObject *ret = PyErr_SetExcFromWindowsErrWithFilenameObject(exc,
                                                                 ierr,
                                                                 name);
    Py_XDECREF(name);
    return ret;
}

PyObject *PyErr_SetExcFromWindowsErrWithUnicodeFilename(
    PyObject *exc,
    int ierr,
    const Py_UNICODE *filename)
{
    PyObject *name = filename ?
                     PyUnicode_FromUnicode(filename, wcslen(filename)) :
             NULL;
    PyObject *ret = PyErr_SetExcFromWindowsErrWithFilenameObject(exc,
                                                                 ierr,
                                                                 name);
    Py_XDECREF(name);
    return ret;
}

PyObject *PyErr_SetExcFromWindowsErr(PyObject *exc, int ierr)
{
    return PyErr_SetExcFromWindowsErrWithFilename(exc, ierr, NULL);
}

PyObject *PyErr_SetFromWindowsErr(int ierr)
{
    return PyErr_SetExcFromWindowsErrWithFilename(PyExc_WindowsError,
                                                  ierr, NULL);
}
PyObject *PyErr_SetFromWindowsErrWithFilename(
    int ierr,
    const char *filename)
{
    PyObject *name = filename ? PyUnicode_FromString(filename) : NULL;
    PyObject *result = PyErr_SetExcFromWindowsErrWithFilenameObject(
                                                  PyExc_WindowsError,
                                                  ierr, name);
    Py_XDECREF(name);
    return result;
}

PyObject *PyErr_SetFromWindowsErrWithUnicodeFilename(
    int ierr,
    const Py_UNICODE *filename)
{
    PyObject *name = filename ?
                     PyUnicode_FromUnicode(filename, wcslen(filename)) :
             NULL;
    PyObject *result = PyErr_SetExcFromWindowsErrWithFilenameObject(
                                                  PyExc_WindowsError,
                                                  ierr, name);
    Py_XDECREF(name);
    return result;
}
#endif /* MS_WINDOWS */

void
_PyErr_BadInternalCall(const char *filename, int lineno)
{
    PyErr_Format(PyExc_SystemError,
                 "%s:%d: bad argument to internal function",
                 filename, lineno);
}

/* Remove the preprocessor macro for PyErr_BadInternalCall() so that we can
   export the entry point for existing object code: */
#undef PyErr_BadInternalCall
void
PyErr_BadInternalCall(void)
{
    PyErr_Format(PyExc_SystemError,
                 "bad argument to internal function");
}
#define PyErr_BadInternalCall() _PyErr_BadInternalCall(__FILE__, __LINE__)



PyObject *
PyErr_Format(PyObject *exception, const char *format, ...)
{
    va_list vargs;
    PyObject* string;

#ifdef HAVE_STDARG_PROTOTYPES
    va_start(vargs, format);
#else
    va_start(vargs);
#endif

    string = PyUnicode_FromFormatV(format, vargs);
    PyErr_SetObject(exception, string);
    Py_XDECREF(string);
    va_end(vargs);
    return NULL;
}



PyObject *
PyErr_NewException(const char *name, PyObject *base, PyObject *dict)
{
    const char *dot;
    PyObject *modulename = NULL;
    PyObject *classname = NULL;
    PyObject *mydict = NULL;
    PyObject *bases = NULL;
    PyObject *result = NULL;
    dot = strrchr(name, '.');
    if (dot == NULL) {
        PyErr_SetString(PyExc_SystemError,
            "PyErr_NewException: name must be module.class");
        return NULL;
    }
    if (base == NULL)
        base = PyExc_Exception;
    if (dict == NULL) {
        dict = mydict = PyDict_New();
        if (dict == NULL)
            goto failure;
    }
    if (PyDict_GetItemString(dict, "__module__") == NULL) {
        modulename = PyUnicode_FromStringAndSize(name,
                                             (Py_ssize_t)(dot-name));
        if (modulename == NULL)
            goto failure;
        if (PyDict_SetItemString(dict, "__module__", modulename) != 0)
            goto failure;
    }
    if (PyTuple_Check(base)) {
        bases = base;
        /* INCREF as we create a new ref in the else branch */
        Py_INCREF(bases);
    } else {
        bases = PyTuple_Pack(1, base);
        if (bases == NULL)
            goto failure;
    }
    /* Create a real new-style class. */
    result = PyObject_CallFunction((PyObject *)&PyType_Type, "sOO",
                                   dot+1, bases, dict);
  failure:
    Py_XDECREF(bases);
    Py_XDECREF(mydict);
    Py_XDECREF(classname);
    Py_XDECREF(modulename);
    return result;
}


/* Create an exception with docstring */
PyObject *
PyErr_NewExceptionWithDoc(const char *name, const char *doc,
                          PyObject *base, PyObject *dict)
{
    int result;
    PyObject *ret = NULL;
    PyObject *mydict = NULL; /* points to the dict only if we create it */
    PyObject *docobj;

    if (dict == NULL) {
        dict = mydict = PyDict_New();
        if (dict == NULL) {
            return NULL;
        }
    }

    if (doc != NULL) {
        docobj = PyUnicode_FromString(doc);
        if (docobj == NULL)
            goto failure;
        result = PyDict_SetItemString(dict, "__doc__", docobj);
        Py_DECREF(docobj);
        if (result < 0)
            goto failure;
    }

    ret = PyErr_NewException(name, base, dict);
  failure:
    Py_XDECREF(mydict);
    return ret;
}


/* Call when an exception has occurred but there is no way for Python
   to handle it.  Examples: exception in __del__ or during GC. */
void
PyErr_WriteUnraisable(PyObject *obj)
{
    PyObject *f, *t, *v, *tb;
    PyErr_Fetch(&t, &v, &tb);
    f = PySys_GetObject("stderr");
    if (f != NULL && f != Py_None) {
        PyFile_WriteString("Exception ", f);
        if (t) {
            PyObject* moduleName;
            char* className;
            assert(PyExceptionClass_Check(t));
            className = PyExceptionClass_Name(t);
            if (className != NULL) {
                char *dot = strrchr(className, '.');
                if (dot != NULL)
                    className = dot+1;
            }

            moduleName = PyObject_GetAttrString(t, "__module__");
            if (moduleName == NULL)
                PyFile_WriteString("<unknown>", f);
            else {
                char* modstr = _PyUnicode_AsString(moduleName);
                if (modstr &&
                    strcmp(modstr, "builtins") != 0)
                {
                    PyFile_WriteString(modstr, f);
                    PyFile_WriteString(".", f);
                }
            }
            if (className == NULL)
                PyFile_WriteString("<unknown>", f);
            else
                PyFile_WriteString(className, f);
            if (v && v != Py_None) {
                PyFile_WriteString(": ", f);
                PyFile_WriteObject(v, f, 0);
            }
            Py_XDECREF(moduleName);
        }
        PyFile_WriteString(" in ", f);
        PyFile_WriteObject(obj, f, 0);
        PyFile_WriteString(" ignored\n", f);
        PyErr_Clear(); /* Just in case */
    }
    Py_XDECREF(t);
    Py_XDECREF(v);
    Py_XDECREF(tb);
}

extern PyObject *PyModule_GetWarningsModule(void);


void
PyErr_SyntaxLocation(const char *filename, int lineno) {
    PyErr_SyntaxLocationEx(filename, lineno, -1);
}


/* Set file and line information for the current exception.
   If the exception is not a SyntaxError, also sets additional attributes
   to make printing of exceptions believe it is a syntax error. */

void
PyErr_SyntaxLocationEx(const char *filename, int lineno, int col_offset)
{
    PyObject *exc, *v, *tb, *tmp;

    /* add attributes for the line number and filename for the error */
    PyErr_Fetch(&exc, &v, &tb);
    PyErr_NormalizeException(&exc, &v, &tb);
    /* XXX check that it is, indeed, a syntax error. It might not
     * be, though. */
    tmp = PyLong_FromLong(lineno);
    if (tmp == NULL)
        PyErr_Clear();
    else {
        if (PyObject_SetAttrString(v, "lineno", tmp))
            PyErr_Clear();
        Py_DECREF(tmp);
    }
    if (col_offset >= 0) {
        tmp = PyLong_FromLong(col_offset);
        if (tmp == NULL)
            PyErr_Clear();
        else {
            if (PyObject_SetAttrString(v, "offset", tmp))
                PyErr_Clear();
            Py_DECREF(tmp);
        }
    }
    if (filename != NULL) {
        tmp = PyUnicode_FromString(filename);
        if (tmp == NULL)
            PyErr_Clear();
        else {
            if (PyObject_SetAttrString(v, "filename", tmp))
                PyErr_Clear();
            Py_DECREF(tmp);
        }

        tmp = PyErr_ProgramText(filename, lineno);
        if (tmp) {
            if (PyObject_SetAttrString(v, "text", tmp))
                PyErr_Clear();
            Py_DECREF(tmp);
        }
    }
    if (PyObject_SetAttrString(v, "offset", Py_None)) {
        PyErr_Clear();
    }
    if (exc != PyExc_SyntaxError) {
        if (!PyObject_HasAttrString(v, "msg")) {
            tmp = PyObject_Str(v);
            if (tmp) {
                if (PyObject_SetAttrString(v, "msg", tmp))
                    PyErr_Clear();
                Py_DECREF(tmp);
            } else {
                PyErr_Clear();
            }
        }
        if (!PyObject_HasAttrString(v, "print_file_and_line")) {
            if (PyObject_SetAttrString(v, "print_file_and_line",
                                       Py_None))
                PyErr_Clear();
        }
    }
    PyErr_Restore(exc, v, tb);
}

/* Attempt to load the line of text that the exception refers to.  If it
   fails, it will return NULL but will not set an exception.

   XXX The functionality of this function is quite similar to the
   functionality in tb_displayline() in traceback.c. */

PyObject *
PyErr_ProgramText(const char *filename, int lineno)
{
    FILE *fp;
    int i;
    char linebuf[1000];

    if (filename == NULL || *filename == '\0' || lineno <= 0)
        return NULL;
    fp = fopen(filename, "r" PY_STDIOTEXTMODE);
    if (fp == NULL)
        return NULL;
    for (i = 0; i < lineno; i++) {
        char *pLastChar = &linebuf[sizeof(linebuf) - 2];
        do {
            *pLastChar = '\0';
            if (Py_UniversalNewlineFgets(linebuf, sizeof linebuf,
                                         fp, NULL) == NULL)
                break;
            /* fgets read *something*; if it didn't get as
               far as pLastChar, it must have found a newline
               or hit the end of the file; if pLastChar is \n,
               it obviously found a newline; else we haven't
               yet seen a newline, so must continue */
        } while (*pLastChar != '\0' && *pLastChar != '\n');
    }
    fclose(fp);
    if (i == lineno) {
        char *p = linebuf;
        PyObject *res;
        while (*p == ' ' || *p == '\t' || *p == '\014')
            p++;
        res = PyUnicode_FromString(p);
        if (res == NULL)
            PyErr_Clear();
        return res;
    }
    return NULL;
}

#ifdef __cplusplus
}
#endif