_tkinter.c

/***********************************************************
Copyright (C) 1994 Steen Lumholt.

                        All Rights Reserved

******************************************************************/

/* _tkinter.c -- Interface to libtk.a and libtcl.a. */

/* TCL/TK VERSION INFO:

    Only Tcl/Tk 8.5.12 and later are supported.  Older versions are not
    supported. Use Python 3.10 or older if you cannot upgrade your
    Tcl/Tk libraries.
*/

/* XXX Further speed-up ideas, involving Tcl 8.0 features:

   - Register a new Tcl type, "Python callable", which can be called more
   efficiently and passed to Tcl_EvalObj() directly (if this is possible).

*/

#ifndef Py_BUILD_CORE_BUILTIN
#  define Py_BUILD_CORE_MODULE 1
#endif

#include "Python.h"
#ifdef MS_WINDOWS
#  include "pycore_fileutils.h"   // _Py_stat()
#endif

#include "pycore_long.h"          // _PyLong_IsNegative()

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

#define CHECK_SIZE(size, elemsize) \
    ((size_t)(size) <= Py_MIN((size_t)INT_MAX, UINT_MAX / (size_t)(elemsize)))

/* If Tcl is compiled for threads, we must also define TCL_THREAD. We define
   it always; if Tcl is not threaded, the thread functions in
   Tcl are empty.  */
#define TCL_THREADS

#ifdef TK_FRAMEWORK
#  include <Tcl/tcl.h>
#  include <Tk/tk.h>
#else
#  include <tcl.h>
#  include <tk.h>
#endif

#include "tkinter.h"

#if TK_HEX_VERSION < 0x0805020c
#error "Tk older than 8.5.12 not supported"
#endif

#ifndef TCL_WITH_EXTERNAL_TOMMATH
#define TCL_NO_TOMMATH_H
#endif
#include <tclTomMath.h>

#if defined(TCL_WITH_EXTERNAL_TOMMATH) || (TK_HEX_VERSION >= 0x08070000)
#define USE_DEPRECATED_TOMMATH_API 0
#else
#define USE_DEPRECATED_TOMMATH_API 1
#endif

#if !(defined(MS_WINDOWS) || defined(__CYGWIN__))
#define HAVE_CREATEFILEHANDLER
#endif

#ifdef HAVE_CREATEFILEHANDLER

/* This bit is to ensure that TCL_UNIX_FD is defined and doesn't interfere
   with the proper calculation of FHANDLETYPE == TCL_UNIX_FD below. */
#ifndef TCL_UNIX_FD
#  ifdef TCL_WIN_SOCKET
#    define TCL_UNIX_FD (! TCL_WIN_SOCKET)
#  else
#    define TCL_UNIX_FD 1
#  endif
#endif

/* Tcl_CreateFileHandler() changed several times; these macros deal with the
   messiness.  In Tcl 8.0 and later, it is not available on Windows (and on
   Unix, only because Jack added it back); when available on Windows, it only
   applies to sockets. */

#ifdef MS_WINDOWS
#define FHANDLETYPE TCL_WIN_SOCKET
#else
#define FHANDLETYPE TCL_UNIX_FD
#endif

/* If Tcl can wait for a Unix file descriptor, define the EventHook() routine
   which uses this to handle Tcl events while the user is typing commands. */

#if FHANDLETYPE == TCL_UNIX_FD
#define WAIT_FOR_STDIN
#endif

#endif /* HAVE_CREATEFILEHANDLER */

/* Use OS native encoding for converting between Python strings and
   Tcl objects.
   On Windows use UTF-16 (or UTF-32 for 32-bit Tcl_UniChar) with the
   "surrogatepass" error handler for converting to/from Tcl Unicode objects.
   On Linux use UTF-8 with the "surrogateescape" error handler for converting
   to/from Tcl String objects. */
#ifdef MS_WINDOWS
#define USE_TCL_UNICODE 1
#else
#define USE_TCL_UNICODE 0
#endif

#if PY_LITTLE_ENDIAN
#define NATIVE_BYTEORDER -1
#else
#define NATIVE_BYTEORDER 1
#endif

#ifdef MS_WINDOWS
#include <conio.h>
#define WAIT_FOR_STDIN

static PyObject *
_get_tcl_lib_path(void)
{
    static PyObject *tcl_library_path = NULL;
    static int already_checked = 0;

    if (already_checked == 0) {
        struct stat stat_buf;
        int stat_return_value;

        PyObject *prefix = PySys_GetObject("prefix");  // borrowed reference
        if (prefix == NULL) {
            return NULL;
        }

        /* Check expected location for an installed Python first */
        tcl_library_path = PyUnicode_FromString("\\tcl\\tcl" TCL_VERSION);
        if (tcl_library_path == NULL) {
            return NULL;
        }
        tcl_library_path = PyUnicode_Concat(prefix, tcl_library_path);
        if (tcl_library_path == NULL) {
            return NULL;
        }
        stat_return_value = _Py_stat(tcl_library_path, &stat_buf);
        if (stat_return_value == -2) {
            return NULL;
        }
        if (stat_return_value == -1) {
            /* install location doesn't exist, reset errno and see if
               we're a repository build */
            errno = 0;
#ifdef Py_TCLTK_DIR
            tcl_library_path = PyUnicode_FromString(
                                    Py_TCLTK_DIR "\\lib\\tcl" TCL_VERSION);
            if (tcl_library_path == NULL) {
                return NULL;
            }
            stat_return_value = _Py_stat(tcl_library_path, &stat_buf);
            if (stat_return_value == -2) {
                return NULL;
            }
            if (stat_return_value == -1) {
                /* tcltkDir for a repository build doesn't exist either,
                   reset errno and leave Tcl to its own devices */
                errno = 0;
                tcl_library_path = NULL;
            }
#else
            tcl_library_path = NULL;
#endif
        }
        already_checked = 1;
    }
    return tcl_library_path;
}
#endif /* MS_WINDOWS */

/* The threading situation is complicated.  Tcl is not thread-safe, except
   when configured with --enable-threads.

   So we need to use a lock around all uses of Tcl.  Previously, the
   Python interpreter lock was used for this.  However, this causes
   problems when other Python threads need to run while Tcl is blocked
   waiting for events.

   To solve this problem, a separate lock for Tcl is introduced.
   Holding it is incompatible with holding Python's interpreter lock.
   The following four macros manipulate both locks together.

   ENTER_TCL and LEAVE_TCL are brackets, just like
   Py_BEGIN_ALLOW_THREADS and Py_END_ALLOW_THREADS.  They should be
   used whenever a call into Tcl is made that could call an event
   handler, or otherwise affect the state of a Tcl interpreter.  These
   assume that the surrounding code has the Python interpreter lock;
   inside the brackets, the Python interpreter lock has been released
   and the lock for Tcl has been acquired.

   Sometimes, it is necessary to have both the Python lock and the Tcl
   lock.  (For example, when transferring data from the Tcl
   interpreter result to a Python string object.)  This can be done by
   using different macros to close the ENTER_TCL block: ENTER_OVERLAP
   reacquires the Python lock (and restores the thread state) but
   doesn't release the Tcl lock; LEAVE_OVERLAP_TCL releases the Tcl
   lock.

   By contrast, ENTER_PYTHON and LEAVE_PYTHON are used in Tcl event
   handlers when the handler needs to use Python.  Such event handlers
   are entered while the lock for Tcl is held; the event handler
   presumably needs to use Python.  ENTER_PYTHON releases the lock for
   Tcl and acquires the Python interpreter lock, restoring the
   appropriate thread state, and LEAVE_PYTHON releases the Python
   interpreter lock and re-acquires the lock for Tcl.  It is okay for
   ENTER_TCL/LEAVE_TCL pairs to be contained inside the code between
   ENTER_PYTHON and LEAVE_PYTHON.

   These locks expand to several statements and brackets; they should
   not be used in branches of if statements and the like.

   If Tcl is threaded, this approach won't work anymore. The Tcl
   interpreter is only valid in the thread that created it, and all Tk
   activity must happen in this thread, also. That means that the
   mainloop must be invoked in the thread that created the
   interpreter. Invoking commands from other threads is possible;
   _tkinter will queue an event for the interpreter thread, which will
   then execute the command and pass back the result. If the main
   thread is not in the mainloop, and invoking commands causes an
   exception; if the main loop is running but not processing events,
   the command invocation will block.

   In addition, for a threaded Tcl, a single global tcl_tstate won't
   be sufficient anymore, since multiple Tcl interpreters may
   simultaneously dispatch in different threads. So we use the Tcl TLS
   API.

*/

static PyThread_type_lock tcl_lock = 0;

#ifdef TCL_THREADS
static Tcl_ThreadDataKey state_key;
typedef PyThreadState *ThreadSpecificData;
#define tcl_tstate \
    (*(PyThreadState**)Tcl_GetThreadData(&state_key, sizeof(PyThreadState*)))
#else
static PyThreadState *tcl_tstate = NULL;
#endif

#define ENTER_TCL \
    { PyThreadState *tstate = PyThreadState_Get(); \
      Py_BEGIN_ALLOW_THREADS \
      if(tcl_lock)PyThread_acquire_lock(tcl_lock, 1); \
      tcl_tstate = tstate;

#define LEAVE_TCL \
    tcl_tstate = NULL; \
    if(tcl_lock)PyThread_release_lock(tcl_lock); \
    Py_END_ALLOW_THREADS}

#define ENTER_OVERLAP \
    Py_END_ALLOW_THREADS

#define LEAVE_OVERLAP_TCL \
    tcl_tstate = NULL; if(tcl_lock)PyThread_release_lock(tcl_lock); }

#define ENTER_PYTHON \
    { PyThreadState *tstate = tcl_tstate; tcl_tstate = NULL; \
      if(tcl_lock) \
        PyThread_release_lock(tcl_lock); \
      PyEval_RestoreThread((tstate)); }

#define LEAVE_PYTHON \
    { PyThreadState *tstate = PyEval_SaveThread(); \
      if(tcl_lock)PyThread_acquire_lock(tcl_lock, 1); \
      tcl_tstate = tstate; }

#define CHECK_TCL_APPARTMENT \
    if (((TkappObject *)self)->threaded && \
        ((TkappObject *)self)->thread_id != Tcl_GetCurrentThread()) { \
        PyErr_SetString(PyExc_RuntimeError, \
                        "Calling Tcl from different apartment"); \
        return 0; \
    }

#ifndef FREECAST
#define FREECAST (char *)
#endif

/**** Tkapp Object Declaration ****/

static PyObject *Tkapp_Type;

typedef struct {
    PyObject_HEAD
    Tcl_Interp *interp;
    int wantobjects;
    int threaded; /* True if tcl_platform[threaded] */
    Tcl_ThreadId thread_id;
    int dispatching;
    /* We cannot include tclInt.h, as this is internal.
       So we cache interesting types here. */
    const Tcl_ObjType *OldBooleanType;
    const Tcl_ObjType *BooleanType;
    const Tcl_ObjType *ByteArrayType;
    const Tcl_ObjType *DoubleType;
    const Tcl_ObjType *IntType;
    const Tcl_ObjType *WideIntType;
    const Tcl_ObjType *BignumType;
    const Tcl_ObjType *ListType;
    const Tcl_ObjType *StringType;
} TkappObject;

#define Tkapp_Interp(v) (((TkappObject *) (v))->interp)


/**** Error Handling ****/

static PyObject *Tkinter_TclError;
static int quitMainLoop = 0;
static int errorInCmd = 0;
static PyObject *excInCmd;


static PyObject *Tkapp_UnicodeResult(TkappObject *);

static PyObject *
Tkinter_Error(TkappObject *self)
{
    PyObject *res = Tkapp_UnicodeResult(self);
    if (res != NULL) {
        PyErr_SetObject(Tkinter_TclError, res);
        Py_DECREF(res);
    }
    return NULL;
}



/**** Utils ****/

static int Tkinter_busywaitinterval = 20;

#ifndef MS_WINDOWS

/* Millisecond sleep() for Unix platforms. */

static void
Sleep(int milli)
{
    /* XXX Too bad if you don't have select(). */
    struct timeval t;
    t.tv_sec = milli/1000;
    t.tv_usec = (milli%1000) * 1000;
    select(0, (fd_set *)0, (fd_set *)0, (fd_set *)0, &t);
}
#endif /* MS_WINDOWS */

/* Wait up to 1s for the mainloop to come up. */

static int
WaitForMainloop(TkappObject* self)
{
    int i;
    for (i = 0; i < 10; i++) {
        if (self->dispatching)
            return 1;
        Py_BEGIN_ALLOW_THREADS
        Sleep(100);
        Py_END_ALLOW_THREADS
    }
    if (self->dispatching)
        return 1;
    PyErr_SetString(PyExc_RuntimeError, "main thread is not in main loop");
    return 0;
}



#define ARGSZ 64



static PyObject *
unicodeFromTclStringAndSize(const char *s, Py_ssize_t size)
{
    PyObject *r = PyUnicode_DecodeUTF8(s, size, NULL);
    if (r != NULL || !PyErr_ExceptionMatches(PyExc_UnicodeDecodeError)) {
        return r;
    }

    char *buf = NULL;
    PyErr_Clear();
    /* Tcl encodes null character as \xc0\x80.
       https://en.wikipedia.org/wiki/UTF-8#Modified_UTF-8 */
    if (memchr(s, '\xc0', size)) {
        char *q;
        const char *e = s + size;
        q = buf = (char *)PyMem_Malloc(size);
        if (buf == NULL) {
            PyErr_NoMemory();
            return NULL;
        }
        while (s != e) {
            if (s + 1 != e && s[0] == '\xc0' && s[1] == '\x80') {
                *q++ = '\0';
                s += 2;
            }
            else
                *q++ = *s++;
        }
        s = buf;
        size = q - s;
    }
    r = PyUnicode_DecodeUTF8(s, size, "surrogateescape");
    if (buf != NULL) {
        PyMem_Free(buf);
    }
    if (r == NULL || PyUnicode_KIND(r) == PyUnicode_1BYTE_KIND) {
        return r;
    }

    /* In CESU-8 non-BMP characters are represented as a surrogate pair,
       like in UTF-16, and then each surrogate code point is encoded in UTF-8.
       https://en.wikipedia.org/wiki/CESU-8 */
    Py_ssize_t len = PyUnicode_GET_LENGTH(r);
    Py_ssize_t i, j;
    /* All encoded surrogate characters start with \xED. */
    i = PyUnicode_FindChar(r, 0xdcED, 0, len, 1);
    if (i == -2) {
        Py_DECREF(r);
        return NULL;
    }
    if (i == -1) {
        return r;
    }
    Py_UCS4 *u = PyUnicode_AsUCS4Copy(r);
    Py_DECREF(r);
    if (u == NULL) {
        return NULL;
    }
    Py_UCS4 ch;
    for (j = i; i < len; i++, u[j++] = ch) {
        Py_UCS4 ch1, ch2, ch3, high, low;
        /* Low surrogates U+D800 - U+DBFF are encoded as
           \xED\xA0\x80 - \xED\xAF\xBF. */
        ch1 = ch = u[i];
        if (ch1 != 0xdcED) continue;
        ch2 = u[i + 1];
        if (!(0xdcA0 <= ch2 && ch2 <= 0xdcAF)) continue;
        ch3 = u[i + 2];
        if (!(0xdc80 <= ch3 && ch3 <= 0xdcBF)) continue;
        high = 0xD000 | ((ch2 & 0x3F) << 6) | (ch3 & 0x3F);
        assert(Py_UNICODE_IS_HIGH_SURROGATE(high));
        /* High surrogates U+DC00 - U+DFFF are encoded as
           \xED\xB0\x80 - \xED\xBF\xBF. */
        ch1 = u[i + 3];
        if (ch1 != 0xdcED) continue;
        ch2 = u[i + 4];
        if (!(0xdcB0 <= ch2 && ch2 <= 0xdcBF)) continue;
        ch3 = u[i + 5];
        if (!(0xdc80 <= ch3 && ch3 <= 0xdcBF)) continue;
        low = 0xD000 | ((ch2 & 0x3F) << 6) | (ch3 & 0x3F);
        assert(Py_UNICODE_IS_HIGH_SURROGATE(high));
        ch = Py_UNICODE_JOIN_SURROGATES(high, low);
        i += 5;
    }
    r = PyUnicode_FromKindAndData(PyUnicode_4BYTE_KIND, u, j);
    PyMem_Free(u);
    return r;
}

static PyObject *
unicodeFromTclString(const char *s)
{
    return unicodeFromTclStringAndSize(s, strlen(s));
}

static PyObject *
unicodeFromTclObj(Tcl_Obj *value)
{
    int len;
#if USE_TCL_UNICODE
    int byteorder = NATIVE_BYTEORDER;
    const Tcl_UniChar *u = Tcl_GetUnicodeFromObj(value, &len);
    if (sizeof(Tcl_UniChar) == 2)
        return PyUnicode_DecodeUTF16((const char *)u, len * 2,
                                     "surrogatepass", &byteorder);
    else if (sizeof(Tcl_UniChar) == 4)
        return PyUnicode_DecodeUTF32((const char *)u, len * 4,
                                     "surrogatepass", &byteorder);
    else
        Py_UNREACHABLE();
#else
    const char *s = Tcl_GetStringFromObj(value, &len);
    return unicodeFromTclStringAndSize(s, len);
#endif
}

/*[clinic input]
module _tkinter
class _tkinter.tkapp "TkappObject *" "&Tkapp_Type_spec"
class _tkinter.Tcl_Obj "PyTclObject *" "&PyTclObject_Type_spec"
class _tkinter.tktimertoken "TkttObject *" "&Tktt_Type_spec"
[clinic start generated code]*/
/*[clinic end generated code: output=da39a3ee5e6b4b0d input=b1ebf15c162ee229]*/

/**** Tkapp Object ****/

#ifndef WITH_APPINIT
int
Tcl_AppInit(Tcl_Interp *interp)
{
    const char * _tkinter_skip_tk_init;

    if (Tcl_Init(interp) == TCL_ERROR) {
        PySys_WriteStderr("Tcl_Init error: %s\n", Tcl_GetStringResult(interp));
        return TCL_ERROR;
    }

    _tkinter_skip_tk_init = Tcl_GetVar(interp,
                    "_tkinter_skip_tk_init", TCL_GLOBAL_ONLY);
    if (_tkinter_skip_tk_init != NULL &&
                    strcmp(_tkinter_skip_tk_init, "1") == 0) {
        return TCL_OK;
    }

    if (Tk_Init(interp) == TCL_ERROR) {
        PySys_WriteStderr("Tk_Init error: %s\n", Tcl_GetStringResult(interp));
        return TCL_ERROR;
    }

    return TCL_OK;
}
#endif /* !WITH_APPINIT */




/* Initialize the Tk application; see the `main' function in
 * `tkMain.c'.
 */

static void EnableEventHook(void); /* Forward */
static void DisableEventHook(void); /* Forward */

static TkappObject *
Tkapp_New(const char *screenName, const char *className,
          int interactive, int wantobjects, int wantTk, int sync,
          const char *use)
{
    TkappObject *v;
    char *argv0;

    v = PyObject_New(TkappObject, (PyTypeObject *) Tkapp_Type);
    if (v == NULL)
        return NULL;

    v->interp = Tcl_CreateInterp();
    v->wantobjects = wantobjects;
    v->threaded = Tcl_GetVar2Ex(v->interp, "tcl_platform", "threaded",
                                TCL_GLOBAL_ONLY) != NULL;
    v->thread_id = Tcl_GetCurrentThread();
    v->dispatching = 0;

#ifndef TCL_THREADS
    if (v->threaded) {
        PyErr_SetString(PyExc_RuntimeError,
                        "Tcl is threaded but _tkinter is not");
        Py_DECREF(v);
        return 0;
    }
#endif
    if (v->threaded && tcl_lock) {
        /* If Tcl is threaded, we don't need the lock. */
        PyThread_free_lock(tcl_lock);
        tcl_lock = NULL;
    }

    v->OldBooleanType = Tcl_GetObjType("boolean");
    v->BooleanType = Tcl_GetObjType("booleanString");
    v->ByteArrayType = Tcl_GetObjType("bytearray");
    v->DoubleType = Tcl_GetObjType("double");
    v->IntType = Tcl_GetObjType("int");
    v->WideIntType = Tcl_GetObjType("wideInt");
    v->BignumType = Tcl_GetObjType("bignum");
    v->ListType = Tcl_GetObjType("list");
    v->StringType = Tcl_GetObjType("string");

    /* Delete the 'exit' command, which can screw things up */
    Tcl_DeleteCommand(v->interp, "exit");

    if (screenName != NULL)
        Tcl_SetVar2(v->interp, "env", "DISPLAY",
                    screenName, TCL_GLOBAL_ONLY);

    if (interactive)
        Tcl_SetVar(v->interp, "tcl_interactive", "1", TCL_GLOBAL_ONLY);
    else
        Tcl_SetVar(v->interp, "tcl_interactive", "0", TCL_GLOBAL_ONLY);

    /* This is used to get the application class for Tk 4.1 and up */
    argv0 = (char*)PyMem_Malloc(strlen(className) + 1);
    if (!argv0) {
        PyErr_NoMemory();
        Py_DECREF(v);
        return NULL;
    }

    strcpy(argv0, className);
    if (Py_ISUPPER(argv0[0]))
        argv0[0] = Py_TOLOWER(argv0[0]);
    Tcl_SetVar(v->interp, "argv0", argv0, TCL_GLOBAL_ONLY);
    PyMem_Free(argv0);

    if (! wantTk) {
        Tcl_SetVar(v->interp,
                        "_tkinter_skip_tk_init", "1", TCL_GLOBAL_ONLY);
    }

    /* some initial arguments need to be in argv */
    if (sync || use) {
        char *args;
        Py_ssize_t len = 0;

        if (sync)
            len += sizeof "-sync";
        if (use)
            len += strlen(use) + sizeof "-use ";  /* never overflows */

        args = (char*)PyMem_Malloc(len);
        if (!args) {
            PyErr_NoMemory();
            Py_DECREF(v);
            return NULL;
        }

        args[0] = '\0';
        if (sync)
            strcat(args, "-sync");
        if (use) {
            if (sync)
                strcat(args, " ");
            strcat(args, "-use ");
            strcat(args, use);
        }

        Tcl_SetVar(v->interp, "argv", args, TCL_GLOBAL_ONLY);
        PyMem_Free(args);
    }

#ifdef MS_WINDOWS
    {
        PyObject *str_path;
        PyObject *utf8_path;
        DWORD ret;

        ret = GetEnvironmentVariableW(L"TCL_LIBRARY", NULL, 0);
        if (!ret && GetLastError() == ERROR_ENVVAR_NOT_FOUND) {
            str_path = _get_tcl_lib_path();
            if (str_path == NULL && PyErr_Occurred()) {
                return NULL;
            }
            if (str_path != NULL) {
                utf8_path = PyUnicode_AsUTF8String(str_path);
                if (utf8_path == NULL) {
                    return NULL;
                }
                Tcl_SetVar(v->interp,
                           "tcl_library",
                           PyBytes_AS_STRING(utf8_path),
                           TCL_GLOBAL_ONLY);
                Py_DECREF(utf8_path);
            }
        }
    }
#endif

    if (Tcl_AppInit(v->interp) != TCL_OK) {
        PyObject *result = Tkinter_Error(v);
        Py_DECREF((PyObject *)v);
        return (TkappObject *)result;
    }

    EnableEventHook();

    return v;
}


static void
Tkapp_ThreadSend(TkappObject *self, Tcl_Event *ev,
                 Tcl_Condition *cond, Tcl_Mutex *mutex)
{
    Py_BEGIN_ALLOW_THREADS;
    Tcl_MutexLock(mutex);
    Tcl_ThreadQueueEvent(self->thread_id, ev, TCL_QUEUE_TAIL);
    Tcl_ThreadAlert(self->thread_id);
    Tcl_ConditionWait(cond, mutex, NULL);
    Tcl_MutexUnlock(mutex);
    Py_END_ALLOW_THREADS
}


/** Tcl Eval **/

typedef struct {
    PyObject_HEAD
    Tcl_Obj *value;
    PyObject *string; /* This cannot cause cycles. */
} PyTclObject;

static PyObject *PyTclObject_Type;
#define PyTclObject_Check(v) Py_IS_TYPE(v, (PyTypeObject *) PyTclObject_Type)

static PyObject *
newPyTclObject(Tcl_Obj *arg)
{
    PyTclObject *self;
    self = PyObject_New(PyTclObject, (PyTypeObject *) PyTclObject_Type);
    if (self == NULL)
        return NULL;
    Tcl_IncrRefCount(arg);
    self->value = arg;
    self->string = NULL;
    return (PyObject*)self;
}

static void
PyTclObject_dealloc(PyObject *_self)
{
    PyTclObject *self = (PyTclObject *)_self;
    PyObject *tp = (PyObject *) Py_TYPE(self);
    Tcl_DecrRefCount(self->value);
    Py_XDECREF(self->string);
    PyObject_Free(self);
    Py_DECREF(tp);
}

/* Like _str, but create Unicode if necessary. */
PyDoc_STRVAR(PyTclObject_string__doc__,
"the string representation of this object, either as str or bytes");

static PyObject *
PyTclObject_string(PyObject *_self, void *ignored)
{
    PyTclObject *self = (PyTclObject *)_self;
    if (!self->string) {
        self->string = unicodeFromTclObj(self->value);
        if (!self->string)
            return NULL;
    }
    return Py_NewRef(self->string);
}

static PyObject *
PyTclObject_str(PyObject *_self)
{
    PyTclObject *self = (PyTclObject *)_self;
    if (self->string) {
        return Py_NewRef(self->string);
    }
    /* XXX Could cache result if it is non-ASCII. */
    return unicodeFromTclObj(self->value);
}

static PyObject *
PyTclObject_repr(PyObject *_self)
{
    PyTclObject *self = (PyTclObject *)_self;
    PyObject *repr, *str = PyTclObject_str(_self);
    if (str == NULL)
        return NULL;
    repr = PyUnicode_FromFormat("<%s object: %R>",
                                self->value->typePtr->name, str);
    Py_DECREF(str);
    return repr;
}

static PyObject *
PyTclObject_richcompare(PyObject *self, PyObject *other, int op)
{
    int result;

    /* neither argument should be NULL, unless something's gone wrong */
    if (self == NULL || other == NULL) {
        PyErr_BadInternalCall();
        return NULL;
    }

    /* both arguments should be instances of PyTclObject */
    if (!PyTclObject_Check(self) || !PyTclObject_Check(other)) {
        Py_RETURN_NOTIMPLEMENTED;
    }

    if (self == other)
        /* fast path when self and other are identical */
        result = 0;
    else
        result = strcmp(Tcl_GetString(((PyTclObject *)self)->value),
                        Tcl_GetString(((PyTclObject *)other)->value));
    Py_RETURN_RICHCOMPARE(result, 0, op);
}

PyDoc_STRVAR(get_typename__doc__, "name of the Tcl type");

static PyObject*
get_typename(PyObject *self, void* ignored)
{
    PyTclObject *obj = (PyTclObject *)self;
    return unicodeFromTclString(obj->value->typePtr->name);
}


static PyGetSetDef PyTclObject_getsetlist[] = {
    {"typename", get_typename, NULL, get_typename__doc__},
    {"string", PyTclObject_string, NULL,
     PyTclObject_string__doc__},
    {0},
};

static PyType_Slot PyTclObject_Type_slots[] = {
    {Py_tp_dealloc, PyTclObject_dealloc},
    {Py_tp_repr, PyTclObject_repr},
    {Py_tp_str, PyTclObject_str},
    {Py_tp_getattro, PyObject_GenericGetAttr},
    {Py_tp_richcompare, PyTclObject_richcompare},
    {Py_tp_getset, PyTclObject_getsetlist},
    {0, 0}
};

static PyType_Spec PyTclObject_Type_spec = {
    "_tkinter.Tcl_Obj",
    sizeof(PyTclObject),
    0,
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_DISALLOW_INSTANTIATION,
    PyTclObject_Type_slots,
};


#if SIZE_MAX > INT_MAX
#define CHECK_STRING_LENGTH(s) do {                                     \
        if (s != NULL && strlen(s) >= INT_MAX) {                        \
            PyErr_SetString(PyExc_OverflowError, "string is too long"); \
            return NULL;                                                \
        } } while(0)
#else
#define CHECK_STRING_LENGTH(s)
#endif

static Tcl_Obj*
asBignumObj(PyObject *value)
{
    Tcl_Obj *result;
    int neg;
    PyObject *hexstr;
    const char *hexchars;
    mp_int bigValue;

    assert(PyLong_Check(value));
    neg = _PyLong_IsNegative((PyLongObject *)value);
    hexstr = _PyLong_Format(value, 16);
    if (hexstr == NULL)
        return NULL;
    hexchars = PyUnicode_AsUTF8(hexstr);
    if (hexchars == NULL) {
        Py_DECREF(hexstr);
        return NULL;
    }
    hexchars += neg + 2; /* skip sign and "0x" */
    if (mp_init(&bigValue) != MP_OKAY ||
        mp_read_radix(&bigValue, hexchars, 16) != MP_OKAY)
    {
        mp_clear(&bigValue);
        Py_DECREF(hexstr);
        PyErr_NoMemory();
        return NULL;
    }
    Py_DECREF(hexstr);
    bigValue.sign = neg ? MP_NEG : MP_ZPOS;
    result = Tcl_NewBignumObj(&bigValue);
    mp_clear(&bigValue);
    if (result == NULL) {
        PyErr_NoMemory();
        return NULL;
    }
    return result;
}

static Tcl_Obj*
AsObj(PyObject *value)
{
    Tcl_Obj *result;

    if (PyBytes_Check(value)) {
        if (PyBytes_GET_SIZE(value) >= INT_MAX) {
            PyErr_SetString(PyExc_OverflowError, "bytes object is too long");
            return NULL;
        }
        return Tcl_NewByteArrayObj((unsigned char *)PyBytes_AS_STRING(value),
                                   (int)PyBytes_GET_SIZE(value));
    }

    if (PyBool_Check(value))
        return Tcl_NewBooleanObj(PyObject_IsTrue(value));

    if (PyLong_CheckExact(value)) {
        int overflow;
        long longValue;
        Tcl_WideInt wideValue;
        longValue = PyLong_AsLongAndOverflow(value, &overflow);
        if (!overflow) {
            return Tcl_NewLongObj(longValue);
        }
        /* If there is an overflow in the long conversion,
           fall through to wideInt handling. */
        if (_PyLong_AsByteArray((PyLongObject *)value,
                                (unsigned char *)(void *)&wideValue,
                                sizeof(wideValue),
                                PY_LITTLE_ENDIAN,
                                /* signed */ 1,
                                /* with_exceptions */ 1) == 0) {
            return Tcl_NewWideIntObj(wideValue);
        }
        PyErr_Clear();
        /* If there is an overflow in the wideInt conversion,
           fall through to bignum handling. */
        return asBignumObj(value);
        /* If there is no wideInt or bignum support,
           fall through to default object handling. */
    }

    if (PyFloat_Check(value))
        return Tcl_NewDoubleObj(PyFloat_AS_DOUBLE(value));

    if (PyTuple_Check(value) || PyList_Check(value)) {
        Tcl_Obj **argv;
        Py_ssize_t size, i;

        size = PySequence_Fast_GET_SIZE(value);
        if (size == 0)
            return Tcl_NewListObj(0, NULL);
        if (!CHECK_SIZE(size, sizeof(Tcl_Obj *))) {
            PyErr_SetString(PyExc_OverflowError,
                            PyTuple_Check(value) ? "tuple is too long" :
                                                   "list is too long");
            return NULL;
        }
        argv = (Tcl_Obj **) PyMem_Malloc(((size_t)size) * sizeof(Tcl_Obj *));
        if (!argv) {
          PyErr_NoMemory();
          return NULL;
        }
        for (i = 0; i < size; i++)
          argv[i] = AsObj(PySequence_Fast_GET_ITEM(value,i));
        result = Tcl_NewListObj((int)size, argv);
        PyMem_Free(argv);
        return result;
    }

    if (PyUnicode_Check(value)) {
        Py_ssize_t size = PyUnicode_GET_LENGTH(value);
        if (size == 0) {
            return Tcl_NewStringObj("", 0);
        }
        if (!CHECK_SIZE(size, sizeof(Tcl_UniChar))) {
            PyErr_SetString(PyExc_OverflowError, "string is too long");
            return NULL;
        }
        if (PyUnicode_IS_ASCII(value)) {
            return Tcl_NewStringObj((const char *)PyUnicode_DATA(value),
                                    (int)size);
        }

        PyObject *encoded;
#if USE_TCL_UNICODE
        if (sizeof(Tcl_UniChar) == 2)
            encoded = _PyUnicode_EncodeUTF16(value,
                    "surrogatepass", NATIVE_BYTEORDER);
        else if (sizeof(Tcl_UniChar) == 4)
            encoded = _PyUnicode_EncodeUTF32(value,
                    "surrogatepass", NATIVE_BYTEORDER);
        else
            Py_UNREACHABLE();
#else
        encoded = _PyUnicode_AsUTF8String(value, "surrogateescape");
#endif
        if (!encoded) {
            return NULL;
        }
        size = PyBytes_GET_SIZE(encoded);
        if (size > INT_MAX) {