pythonrun.c

/* Python interpreter top-level routines, including init/exit */

#include "Python.h"

#include "Python-ast.h"
#undef Yield /* undefine macro conflicting with winbase.h */
#include "grammar.h"
#include "node.h"
#include "token.h"
#include "parsetok.h"
#include "errcode.h"
#include "code.h"
#include "symtable.h"
#include "ast.h"
#include "marshal.h"
#include "osdefs.h"
#include <locale.h>

#ifdef HAVE_SIGNAL_H
#include <signal.h>
#endif

#ifdef MS_WINDOWS
#include "malloc.h" /* for alloca */
#endif

#ifdef HAVE_LANGINFO_H
#include <langinfo.h>
#endif

#ifdef MS_WINDOWS
#undef BYTE
#include "windows.h"
#endif

_Py_IDENTIFIER(builtins);
_Py_IDENTIFIER(excepthook);
_Py_IDENTIFIER(flush);
_Py_IDENTIFIER(last_traceback);
_Py_IDENTIFIER(last_type);
_Py_IDENTIFIER(last_value);
_Py_IDENTIFIER(ps1);
_Py_IDENTIFIER(ps2);
_Py_IDENTIFIER(stdin);
_Py_IDENTIFIER(stdout);
_Py_IDENTIFIER(stderr);
_Py_static_string(PyId_string, "<string>");

#ifdef __cplusplus
extern "C" {
#endif

extern grammar _PyParser_Grammar; /* From graminit.c */

/* Forward */
static void flush_io(void);
static PyObject *run_mod(mod_ty, PyObject *, PyObject *, PyObject *,
                          PyCompilerFlags *, PyArena *);
static PyObject *run_pyc_file(FILE *, const char *, PyObject *, PyObject *,
                              PyCompilerFlags *);
static void err_input(perrdetail *);
static void err_free(perrdetail *);

/* Parse input from a file and execute it */

int
PyRun_AnyFileExFlags(FILE *fp, const char *filename, int closeit,
                     PyCompilerFlags *flags)
{
    if (filename == NULL)
        filename = "???";
    if (Py_FdIsInteractive(fp, filename)) {
        int err = PyRun_InteractiveLoopFlags(fp, filename, flags);
        if (closeit)
            fclose(fp);
        return err;
    }
    else
        return PyRun_SimpleFileExFlags(fp, filename, closeit, flags);
}

int
PyRun_InteractiveLoopFlags(FILE *fp, const char *filename_str, PyCompilerFlags *flags)
{
    PyObject *filename, *v;
    int ret, err;
    PyCompilerFlags local_flags;

    filename = PyUnicode_DecodeFSDefault(filename_str);
    if (filename == NULL) {
        PyErr_Print();
        return -1;
    }

    if (flags == NULL) {
        flags = &local_flags;
        local_flags.cf_flags = 0;
    }
    v = _PySys_GetObjectId(&PyId_ps1);
    if (v == NULL) {
        _PySys_SetObjectId(&PyId_ps1, v = PyUnicode_FromString(">>> "));
        Py_XDECREF(v);
    }
    v = _PySys_GetObjectId(&PyId_ps2);
    if (v == NULL) {
        _PySys_SetObjectId(&PyId_ps2, v = PyUnicode_FromString("... "));
        Py_XDECREF(v);
    }
    err = -1;
    for (;;) {
        ret = PyRun_InteractiveOneObject(fp, filename, flags);
        _PY_DEBUG_PRINT_TOTAL_REFS();
        if (ret == E_EOF) {
            err = 0;
            break;
        }
        /*
        if (ret == E_NOMEM)
            break;
        */
    }
    Py_DECREF(filename);
    return err;
}

/* compute parser flags based on compiler flags */
static int PARSER_FLAGS(PyCompilerFlags *flags)
{
    int parser_flags = 0;
    if (!flags)
        return 0;
    if (flags->cf_flags & PyCF_DONT_IMPLY_DEDENT)
        parser_flags |= PyPARSE_DONT_IMPLY_DEDENT;
    if (flags->cf_flags & PyCF_IGNORE_COOKIE)
        parser_flags |= PyPARSE_IGNORE_COOKIE;
    if (flags->cf_flags & CO_FUTURE_BARRY_AS_BDFL)
        parser_flags |= PyPARSE_BARRY_AS_BDFL;
    return parser_flags;
}

#if 0
/* Keep an example of flags with future keyword support. */
#define PARSER_FLAGS(flags) \
    ((flags) ? ((((flags)->cf_flags & PyCF_DONT_IMPLY_DEDENT) ? \
                  PyPARSE_DONT_IMPLY_DEDENT : 0) \
                | ((flags)->cf_flags & CO_FUTURE_WITH_STATEMENT ? \
                   PyPARSE_WITH_IS_KEYWORD : 0)) : 0)
#endif

int
PyRun_InteractiveOneObject(FILE *fp, PyObject *filename, PyCompilerFlags *flags)
{
    PyObject *m, *d, *v, *w, *oenc = NULL, *mod_name;
    mod_ty mod;
    PyArena *arena;
    char *ps1 = "", *ps2 = "", *enc = NULL;
    int errcode = 0;
    _Py_IDENTIFIER(encoding);
    _Py_IDENTIFIER(__main__);

    mod_name = _PyUnicode_FromId(&PyId___main__); /* borrowed */
    if (mod_name == NULL) {
        PyErr_Print();
        return -1;
    }

    if (fp == stdin) {
        /* Fetch encoding from sys.stdin if possible. */
        v = _PySys_GetObjectId(&PyId_stdin);
        if (v && v != Py_None) {
            oenc = _PyObject_GetAttrId(v, &PyId_encoding);
            if (oenc)
                enc = _PyUnicode_AsString(oenc);
            if (!enc)
                PyErr_Clear();
        }
    }
    v = _PySys_GetObjectId(&PyId_ps1);
    if (v != NULL) {
        v = PyObject_Str(v);
        if (v == NULL)
            PyErr_Clear();
        else if (PyUnicode_Check(v)) {
            ps1 = _PyUnicode_AsString(v);
            if (ps1 == NULL) {
                PyErr_Clear();
                ps1 = "";
            }
        }
    }
    w = _PySys_GetObjectId(&PyId_ps2);
    if (w != NULL) {
        w = PyObject_Str(w);
        if (w == NULL)
            PyErr_Clear();
        else if (PyUnicode_Check(w)) {
            ps2 = _PyUnicode_AsString(w);
            if (ps2 == NULL) {
                PyErr_Clear();
                ps2 = "";
            }
        }
    }
    arena = PyArena_New();
    if (arena == NULL) {
        Py_XDECREF(v);
        Py_XDECREF(w);
        Py_XDECREF(oenc);
        return -1;
    }
    mod = PyParser_ASTFromFileObject(fp, filename, enc,
                                     Py_single_input, ps1, ps2,
                                     flags, &errcode, arena);
    Py_XDECREF(v);
    Py_XDECREF(w);
    Py_XDECREF(oenc);
    if (mod == NULL) {
        PyArena_Free(arena);
        if (errcode == E_EOF) {
            PyErr_Clear();
            return E_EOF;
        }
        PyErr_Print();
        return -1;
    }
    m = PyImport_AddModuleObject(mod_name);
    if (m == NULL) {
        PyArena_Free(arena);
        return -1;
    }
    d = PyModule_GetDict(m);
    v = run_mod(mod, filename, d, d, flags, arena);
    PyArena_Free(arena);
    if (v == NULL) {
        PyErr_Print();
        flush_io();
        return -1;
    }
    Py_DECREF(v);
    flush_io();
    return 0;
}

int
PyRun_InteractiveOneFlags(FILE *fp, const char *filename_str, PyCompilerFlags *flags)
{
    PyObject *filename;
    int res;

    filename = PyUnicode_DecodeFSDefault(filename_str);
    if (filename == NULL) {
        PyErr_Print();
        return -1;
    }
    res = PyRun_InteractiveOneObject(fp, filename, flags);
    Py_DECREF(filename);
    return res;
}


/* Issue #29537: handle issue27286 bytecode incompatibility
 *   See Lib/importlib/_bootstrap_external.py for general discussion
 */
extern PY_UINT32_T _Py_BACKCOMPAT_HALF_MAGIC;
static int
_check_half_magic(unsigned int read_value, unsigned int halfmagic) {
    return (read_value == halfmagic || read_value == _Py_BACKCOMPAT_HALF_MAGIC);
}

extern PY_UINT32_T _Py_BACKCOMPAT_MAGIC_NUMBER;
static int
_check_magic(long read_value, long magic) {
    return (read_value == magic || read_value == _Py_BACKCOMPAT_MAGIC_NUMBER);
}

/* Check whether a file maybe a pyc file: Look at the extension,
   the file type, and, if we may close it, at the first few bytes. */

static int
maybe_pyc_file(FILE *fp, const char* filename, const char* ext, int closeit)
{
    if (strcmp(ext, ".pyc") == 0)
        return 1;

    /* Only look into the file if we are allowed to close it, since
       it then should also be seekable. */
    if (closeit) {
        /* Read only two bytes of the magic. If the file was opened in
           text mode, the bytes 3 and 4 of the magic (\r\n) might not
           be read as they are on disk. */
        unsigned int halfmagic = PyImport_GetMagicNumber() & 0xFFFF;
        unsigned char buf[2];
        /* Mess:  In case of -x, the stream is NOT at its start now,
           and ungetc() was used to push back the first newline,
           which makes the current stream position formally undefined,
           and a x-platform nightmare.
           Unfortunately, we have no direct way to know whether -x
           was specified.  So we use a terrible hack:  if the current
           stream position is not 0, we assume -x was specified, and
           give up.  Bug 132850 on SourceForge spells out the
           hopelessness of trying anything else (fseek and ftell
           don't work predictably x-platform for text-mode files).
        */
        int ispyc = 0;
        if (ftell(fp) == 0) {
            if (fread(buf, 1, 2, fp) == 2 &&
                _check_half_magic(((unsigned int)buf[1]<<8 | buf[0]), halfmagic))
                ispyc = 1;
            rewind(fp);
        }
        return ispyc;
    }
    return 0;
}

static int
set_main_loader(PyObject *d, const char *filename, const char *loader_name)
{
    PyInterpreterState *interp;
    PyThreadState *tstate;
    PyObject *filename_obj, *bootstrap, *loader_type = NULL, *loader;
    int result = 0;

    filename_obj = PyUnicode_DecodeFSDefault(filename);
    if (filename_obj == NULL)
        return -1;
    /* Get current thread state and interpreter pointer */
    tstate = PyThreadState_GET();
    interp = tstate->interp;
    bootstrap = PyObject_GetAttrString(interp->importlib,
                                       "_bootstrap_external");
    if (bootstrap != NULL) {
        loader_type = PyObject_GetAttrString(bootstrap, loader_name);
        Py_DECREF(bootstrap);
    }
    if (loader_type == NULL) {
        Py_DECREF(filename_obj);
        return -1;
    }
    loader = PyObject_CallFunction(loader_type, "sN", "__main__", filename_obj);
    Py_DECREF(loader_type);
    if (loader == NULL) {
        return -1;
    }
    if (PyDict_SetItemString(d, "__loader__", loader) < 0) {
        result = -1;
    }
    Py_DECREF(loader);
    return result;
}

int
PyRun_SimpleFileExFlags(FILE *fp, const char *filename, int closeit,
                        PyCompilerFlags *flags)
{
    PyObject *m, *d, *v;
    const char *ext;
    int set_file_name = 0, ret = -1;
    size_t len;

    m = PyImport_AddModule("__main__");
    if (m == NULL)
        return -1;
    Py_INCREF(m);
    d = PyModule_GetDict(m);
    if (PyDict_GetItemString(d, "__file__") == NULL) {
        PyObject *f;
        f = PyUnicode_DecodeFSDefault(filename);
        if (f == NULL)
            goto done;
        if (PyDict_SetItemString(d, "__file__", f) < 0) {
            Py_DECREF(f);
            goto done;
        }
        if (PyDict_SetItemString(d, "__cached__", Py_None) < 0) {
            Py_DECREF(f);
            goto done;
        }
        set_file_name = 1;
        Py_DECREF(f);
    }
    len = strlen(filename);
    ext = filename + len - (len > 4 ? 4 : 0);
    if (maybe_pyc_file(fp, filename, ext, closeit)) {
        FILE *pyc_fp;
        /* Try to run a pyc file. First, re-open in binary */
        if (closeit)
            fclose(fp);
        if ((pyc_fp = _Py_fopen(filename, "rb")) == NULL) {
            fprintf(stderr, "python: Can't reopen .pyc file\n");
            goto done;
        }

        if (set_main_loader(d, filename, "SourcelessFileLoader") < 0) {
            fprintf(stderr, "python: failed to set __main__.__loader__\n");
            ret = -1;
            fclose(pyc_fp);
            goto done;
        }
        v = run_pyc_file(pyc_fp, filename, d, d, flags);
        fclose(pyc_fp);
    } else {
        /* When running from stdin, leave __main__.__loader__ alone */
        if (strcmp(filename, "<stdin>") != 0 &&
            set_main_loader(d, filename, "SourceFileLoader") < 0) {
            fprintf(stderr, "python: failed to set __main__.__loader__\n");
            ret = -1;
            goto done;
        }
        v = PyRun_FileExFlags(fp, filename, Py_file_input, d, d,
                              closeit, flags);
    }
    flush_io();
    if (v == NULL) {
        PyErr_Print();
        goto done;
    }
    Py_DECREF(v);
    ret = 0;
  done:
    if (set_file_name && PyDict_DelItemString(d, "__file__"))
        PyErr_Clear();
    Py_DECREF(m);
    return ret;
}

int
PyRun_SimpleStringFlags(const char *command, PyCompilerFlags *flags)
{
    PyObject *m, *d, *v;
    m = PyImport_AddModule("__main__");
    if (m == NULL)
        return -1;
    d = PyModule_GetDict(m);
    v = PyRun_StringFlags(command, Py_file_input, d, d, flags);
    if (v == NULL) {
        PyErr_Print();
        return -1;
    }
    Py_DECREF(v);
    return 0;
}

static int
parse_syntax_error(PyObject *err, PyObject **message, PyObject **filename,
                   int *lineno, int *offset, PyObject **text)
{
    long hold;
    PyObject *v;
    _Py_IDENTIFIER(msg);
    _Py_IDENTIFIER(filename);
    _Py_IDENTIFIER(lineno);
    _Py_IDENTIFIER(offset);
    _Py_IDENTIFIER(text);

    *message = NULL;
    *filename = NULL;

    /* new style errors.  `err' is an instance */
    *message = _PyObject_GetAttrId(err, &PyId_msg);
    if (!*message)
        goto finally;

    v = _PyObject_GetAttrId(err, &PyId_filename);
    if (!v)
        goto finally;
    if (v == Py_None) {
        Py_DECREF(v);
        *filename = _PyUnicode_FromId(&PyId_string);
        if (*filename == NULL)
            goto finally;
        Py_INCREF(*filename);
    }
    else {
        *filename = v;
    }

    v = _PyObject_GetAttrId(err, &PyId_lineno);
    if (!v)
        goto finally;
    hold = PyLong_AsLong(v);
    Py_DECREF(v);
    if (hold < 0 && PyErr_Occurred())
        goto finally;
    *lineno = (int)hold;

    v = _PyObject_GetAttrId(err, &PyId_offset);
    if (!v)
        goto finally;
    if (v == Py_None) {
        *offset = -1;
        Py_DECREF(v);
    } else {
        hold = PyLong_AsLong(v);
        Py_DECREF(v);
        if (hold < 0 && PyErr_Occurred())
            goto finally;
        *offset = (int)hold;
    }

    v = _PyObject_GetAttrId(err, &PyId_text);
    if (!v)
        goto finally;
    if (v == Py_None) {
        Py_DECREF(v);
        *text = NULL;
    }
    else {
        *text = v;
    }
    return 1;

finally:
    Py_XDECREF(*message);
    Py_XDECREF(*filename);
    return 0;
}

void
PyErr_Print(void)
{
    PyErr_PrintEx(1);
}

static void
print_error_text(PyObject *f, int offset, PyObject *text_obj)
{
    char *text;
    char *nl;

    text = _PyUnicode_AsString(text_obj);
    if (text == NULL)
        return;

    if (offset >= 0) {
        if (offset > 0 && (size_t)offset == strlen(text) && text[offset - 1] == '\n')
            offset--;
        for (;;) {
            nl = strchr(text, '\n');
            if (nl == NULL || nl-text >= offset)
                break;
            offset -= (int)(nl+1-text);
            text = nl+1;
        }
        while (*text == ' ' || *text == '\t' || *text == '\f') {
            text++;
            offset--;
        }
    }
    PyFile_WriteString("    ", f);
    PyFile_WriteString(text, f);
    if (*text == '\0' || text[strlen(text)-1] != '\n')
        PyFile_WriteString("\n", f);
    if (offset == -1)
        return;
    PyFile_WriteString("    ", f);
    while (--offset > 0)
        PyFile_WriteString(" ", f);
    PyFile_WriteString("^\n", f);
}

static void
handle_system_exit(void)
{
    PyObject *exception, *value, *tb;
    int exitcode = 0;

    if (Py_InspectFlag)
        /* Don't exit if -i flag was given. This flag is set to 0
         * when entering interactive mode for inspecting. */
        return;

    PyErr_Fetch(&exception, &value, &tb);
    fflush(stdout);
    if (value == NULL || value == Py_None)
        goto done;
    if (PyExceptionInstance_Check(value)) {
        /* The error code should be in the `code' attribute. */
        _Py_IDENTIFIER(code);
        PyObject *code = _PyObject_GetAttrId(value, &PyId_code);
        if (code) {
            Py_DECREF(value);
            value = code;
            if (value == Py_None)
                goto done;
        }
        /* If we failed to dig out the 'code' attribute,
           just let the else clause below print the error. */
    }
    if (PyLong_Check(value))
        exitcode = (int)PyLong_AsLong(value);
    else {
        PyObject *sys_stderr = _PySys_GetObjectId(&PyId_stderr);
        /* We clear the exception here to avoid triggering the assertion
         * in PyObject_Str that ensures it won't silently lose exception
         * details.
         */
        PyErr_Clear();
        if (sys_stderr != NULL && sys_stderr != Py_None) {
            PyFile_WriteObject(value, sys_stderr, Py_PRINT_RAW);
        } else {
            PyObject_Print(value, stderr, Py_PRINT_RAW);
            fflush(stderr);
        }
        PySys_WriteStderr("\n");
        exitcode = 1;
    }
 done:
    /* Restore and clear the exception info, in order to properly decref
     * the exception, value, and traceback.      If we just exit instead,
     * these leak, which confuses PYTHONDUMPREFS output, and may prevent
     * some finalizers from running.
     */
    PyErr_Restore(exception, value, tb);
    PyErr_Clear();
    Py_Exit(exitcode);
    /* NOTREACHED */
}

void
PyErr_PrintEx(int set_sys_last_vars)
{
    PyObject *exception, *v, *tb, *hook;

    if (PyErr_ExceptionMatches(PyExc_SystemExit)) {
        handle_system_exit();
    }
    PyErr_Fetch(&exception, &v, &tb);
    if (exception == NULL)
        return;
    PyErr_NormalizeException(&exception, &v, &tb);
    if (tb == NULL) {
        tb = Py_None;
        Py_INCREF(tb);
    }
    PyException_SetTraceback(v, tb);
    if (exception == NULL)
        return;
    /* Now we know v != NULL too */
    if (set_sys_last_vars) {
        _PySys_SetObjectId(&PyId_last_type, exception);
        _PySys_SetObjectId(&PyId_last_value, v);
        _PySys_SetObjectId(&PyId_last_traceback, tb);
    }
    hook = _PySys_GetObjectId(&PyId_excepthook);
    if (hook) {
        PyObject *args = PyTuple_Pack(3, exception, v, tb);
        PyObject *result = PyEval_CallObject(hook, args);
        if (result == NULL) {
            PyObject *exception2, *v2, *tb2;
            if (PyErr_ExceptionMatches(PyExc_SystemExit)) {
                handle_system_exit();
            }
            PyErr_Fetch(&exception2, &v2, &tb2);
            PyErr_NormalizeException(&exception2, &v2, &tb2);
            /* It should not be possible for exception2 or v2
               to be NULL. However PyErr_Display() can't
               tolerate NULLs, so just be safe. */
            if (exception2 == NULL) {
                exception2 = Py_None;
                Py_INCREF(exception2);
            }
            if (v2 == NULL) {
                v2 = Py_None;
                Py_INCREF(v2);
            }
            fflush(stdout);
            PySys_WriteStderr("Error in sys.excepthook:\n");
            PyErr_Display(exception2, v2, tb2);
            PySys_WriteStderr("\nOriginal exception was:\n");
            PyErr_Display(exception, v, tb);
            Py_DECREF(exception2);
            Py_DECREF(v2);
            Py_XDECREF(tb2);
        }
        Py_XDECREF(result);
        Py_XDECREF(args);
    } else {
        PySys_WriteStderr("sys.excepthook is missing\n");
        PyErr_Display(exception, v, tb);
    }
    Py_XDECREF(exception);
    Py_XDECREF(v);
    Py_XDECREF(tb);
}

static void
print_exception(PyObject *f, PyObject *value)
{
    int err = 0;
    PyObject *type, *tb;
    _Py_IDENTIFIER(print_file_and_line);

    if (!PyExceptionInstance_Check(value)) {
        err = PyFile_WriteString("TypeError: print_exception(): Exception expected for value, ", f);
        err += PyFile_WriteString(Py_TYPE(value)->tp_name, f);
        err += PyFile_WriteString(" found\n", f);
        if (err)
            PyErr_Clear();
        return;
    }

    Py_INCREF(value);
    fflush(stdout);
    type = (PyObject *) Py_TYPE(value);
    tb = PyException_GetTraceback(value);
    if (tb && tb != Py_None)
        err = PyTraceBack_Print(tb, f);
    if (err == 0 &&
        _PyObject_HasAttrId(value, &PyId_print_file_and_line))
    {
        PyObject *message, *filename, *text;
        int lineno, offset;
        if (!parse_syntax_error(value, &message, &filename,
                                &lineno, &offset, &text))
            PyErr_Clear();
        else {
            PyObject *line;

            Py_DECREF(value);
            value = message;

            line = PyUnicode_FromFormat("  File \"%U\", line %d\n",
                                          filename, lineno);
            Py_DECREF(filename);
            if (line != NULL) {
                PyFile_WriteObject(line, f, Py_PRINT_RAW);
                Py_DECREF(line);
            }

            if (text != NULL) {
                print_error_text(f, offset, text);
                Py_DECREF(text);
            }

            /* Can't be bothered to check all those
               PyFile_WriteString() calls */
            if (PyErr_Occurred())
                err = -1;
        }
    }
    if (err) {
        /* Don't do anything else */
    }
    else {
        PyObject* moduleName;
        char* className;
        _Py_IDENTIFIER(__module__);
        assert(PyExceptionClass_Check(type));
        className = PyExceptionClass_Name(type);
        if (className != NULL) {
            char *dot = strrchr(className, '.');
            if (dot != NULL)
                className = dot+1;
        }

        moduleName = _PyObject_GetAttrId(type, &PyId___module__);
        if (moduleName == NULL || !PyUnicode_Check(moduleName))
        {
            Py_XDECREF(moduleName);
            err = PyFile_WriteString("<unknown>", f);
        }
        else {
            if (!_PyUnicode_EqualToASCIIId(moduleName, &PyId_builtins))
            {
                err = PyFile_WriteObject(moduleName, f, Py_PRINT_RAW);
                err += PyFile_WriteString(".", f);
            }
            Py_DECREF(moduleName);
        }
        if (err == 0) {
            if (className == NULL)
                      err = PyFile_WriteString("<unknown>", f);
            else
                      err = PyFile_WriteString(className, f);
        }
    }
    if (err == 0 && (value != Py_None)) {
        PyObject *s = PyObject_Str(value);
        /* only print colon if the str() of the
           object is not the empty string
        */
        if (s == NULL) {
            PyErr_Clear();
            err = -1;
            PyFile_WriteString(": <exception str() failed>", f);
        }
        else if (!PyUnicode_Check(s) ||
            PyUnicode_GetLength(s) != 0)
            err = PyFile_WriteString(": ", f);
        if (err == 0)
          err = PyFile_WriteObject(s, f, Py_PRINT_RAW);
        Py_XDECREF(s);
    }
    /* try to write a newline in any case */
    if (err < 0) {
        PyErr_Clear();
    }
    err += PyFile_WriteString("\n", f);
    Py_XDECREF(tb);
    Py_DECREF(value);
    /* If an error happened here, don't show it.
       XXX This is wrong, but too many callers rely on this behavior. */
    if (err != 0)
        PyErr_Clear();
}

static const char *cause_message =
    "\nThe above exception was the direct cause "
    "of the following exception:\n\n";

static const char *context_message =
    "\nDuring handling of the above exception, "
    "another exception occurred:\n\n";

static void
print_exception_recursive(PyObject *f, PyObject *value, PyObject *seen)
{
    int err = 0, res;
    PyObject *cause, *context;

    if (seen != NULL) {
        /* Exception chaining */
        if (PySet_Add(seen, value) == -1)
            PyErr_Clear();
        else if (PyExceptionInstance_Check(value)) {
            cause = PyException_GetCause(value);
            context = PyException_GetContext(value);
            if (cause) {
                res = PySet_Contains(seen, cause);
                if (res == -1)
                    PyErr_Clear();
                if (res == 0) {
                    print_exception_recursive(
                        f, cause, seen);
                    err |= PyFile_WriteString(
                        cause_message, f);
                }
            }
            else if (context &&
                !((PyBaseExceptionObject *)value)->suppress_context) {
                res = PySet_Contains(seen, context);
                if (res == -1)
                    PyErr_Clear();
                if (res == 0) {
                    print_exception_recursive(
                        f, context, seen);
                    err |= PyFile_WriteString(
                        context_message, f);
                }
            }
            Py_XDECREF(context);
            Py_XDECREF(cause);
        }
    }
    print_exception(f, value);
    if (err != 0)
        PyErr_Clear();
}

void
PyErr_Display(PyObject *exception, PyObject *value, PyObject *tb)
{
    PyObject *seen;
    PyObject *f = _PySys_GetObjectId(&PyId_stderr);
    if (PyExceptionInstance_Check(value)
        && tb != NULL && PyTraceBack_Check(tb)) {
        /* Put the traceback on the exception, otherwise it won't get
           displayed.  See issue #18776. */
        PyObject *cur_tb = PyException_GetTraceback(value);
        if (cur_tb == NULL)
            PyException_SetTraceback(value, tb);
        else
            Py_DECREF(cur_tb);
    }
    if (f == Py_None) {
        /* pass */
    }
    else if (f == NULL) {
        _PyObject_Dump(value);
        fprintf(stderr, "lost sys.stderr\n");
    }
    else {
        /* We choose to ignore seen being possibly NULL, and report
           at least the main exception (it could be a MemoryError).
        */
        seen = PySet_New(NULL);
        if (seen == NULL)
            PyErr_Clear();
        print_exception_recursive(f, value, seen);
        Py_XDECREF(seen);
    }
}

PyObject *
PyRun_StringFlags(const char *str, int start, PyObject *globals,
                  PyObject *locals, PyCompilerFlags *flags)
{
    PyObject *ret = NULL;
    mod_ty mod;
    PyArena *arena;
    PyObject *filename;

    filename = _PyUnicode_FromId(&PyId_string); /* borrowed */
    if (filename == NULL)
        return NULL;

    arena = PyArena_New();
    if (arena == NULL)
        return NULL;

    mod = PyParser_ASTFromStringObject(str, filename, start, flags, arena);
    if (mod != NULL)
        ret = run_mod(mod, filename, globals, locals, flags, arena);
    PyArena_Free(arena);
    return ret;
}

PyObject *
PyRun_FileExFlags(FILE *fp, const char *filename_str, int start, PyObject *globals,
                  PyObject *locals, int closeit, PyCompilerFlags *flags)
{
    PyObject *ret = NULL;
    mod_ty mod;
    PyArena *arena = NULL;
    PyObject *filename;

    filename = PyUnicode_DecodeFSDefault(filename_str);
    if (filename == NULL)
        goto exit;

    arena = PyArena_New();
    if (arena == NULL)
        goto exit;

    mod = PyParser_ASTFromFileObject(fp, filename, NULL, start, 0, 0,
                                     flags, NULL, arena);
    if (closeit)
        fclose(fp);
    if (mod == NULL) {
        goto exit;
    }
    ret = run_mod(mod, filename, globals, locals, flags, arena);

exit:
    Py_XDECREF(filename);
    if (arena != NULL)
        PyArena_Free(arena);
    return ret;
}

static void
flush_io(void)
{
    PyObject *f, *r;
    PyObject *type, *value, *traceback;

    /* Save the current exception */
    PyErr_Fetch(&type, &value, &traceback);

    f = _PySys_GetObjectId(&PyId_stderr);
    if (f != NULL) {
        r = _PyObject_CallMethodId(f, &PyId_flush, "");
        if (r)
            Py_DECREF(r);
        else
            PyErr_Clear();
    }
    f = _PySys_GetObjectId(&PyId_stdout);
    if (f != NULL) {
        r = _PyObject_CallMethodId(f, &PyId_flush, "");
        if (r)
            Py_DECREF(r);
        else
            PyErr_Clear();
    }

    PyErr_Restore(type, value, traceback);
}

static PyObject *
run_mod(mod_ty mod, PyObject *filename, PyObject *globals, PyObject *locals,
            PyCompilerFlags *flags, PyArena *arena)
{
    PyCodeObject *co;
    PyObject *v;
    co = PyAST_CompileObject(mod, filename, flags, -1, arena);
    if (co == NULL)
        return NULL;
    v = PyEval_EvalCode((PyObject*)co, globals, locals);
    Py_DECREF(co);
    return v;
}

static PyObject *
run_pyc_file(FILE *fp, const char *filename, PyObject *globals,
             PyObject *locals, PyCompilerFlags *flags)
{
    PyCodeObject *co;