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Dead code in tkinter #140494
Description
Bug report
Bug description:
Modules/_tkinter.c always defines TCL_THREADS:
/* 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_THREADSbut in two places in Modules/_tkinter.c , we check if TCL_THREADS is defined:
#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;
#endifand
#ifndef TCL_THREADS
if (v->threaded) {
PyErr_SetString(PyExc_RuntimeError,
"Tcl is threaded but _tkinter is not");
Py_DECREF(v);
return 0;
}
#endifEspecially the latter is confusing, as this code block is not compiled and the test is never executed.
CPython versions tested on:
CPython main branch
Operating systems tested on:
No response
Activity
terryjreedy commentedon Oct 23, 2025
tcl/tk 8.5 was by default compiled without thread_support. 8.6 by default is, and perhaps the option is gone. Thread support was once optional in python, but now is mandatory so _tkinter should support them also.
I suspect that the define and the comment before could be eliminated (if these are the only two uses) and the code between
#ifdef TCL_THREADSand #ELSE# made unconditional and the other code eliminated. @serhiy-storchaka ?serhiy-storchaka commentedon Oct 23, 2025
It was unconditionally enabled in b5bfb9f, 23 years ago. Well, I think we can remove this code now. Note that some comments may be need to be updated.
mdehoon commentedon Oct 24, 2025
We still need to #define TCL_THREADS , otherwise tkinter won't compile.
Should we require that tcl/tk was compiled with thread support, or should we still allow tcl/tk without thread support?
serhiy-storchaka commentedon Jul 17, 2026
I think we can drop support of non-threaded Tcl/Tk in main. AFAIK, 8.6 is threaded by default, and 9.0 is always threaded. But the minimal supported version was still 8.5.12. Some distributors can still need to build without threaded support, they may even patch
#define TCL_THREADS. So this is main-only change.To make backporting easier, it is better to hold these changes until we fix other issues.