Dead code in tkinter

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_THREADS

but 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;
#endif

and

#ifndef TCL_THREADS
    if (v->threaded) {
        PyErr_SetString(PyExc_RuntimeError,
                        "Tcl is threaded but _tkinter is not");
        Py_DECREF(v);
        return 0;
    }
#endif

Especially 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

Linked PRs

• gh-141241
• gh-152841

从 Modules/_tkinter.c 开始，阅读 TCL_THREADS 定义和报告中显示的两个条件代码块，然后查看链接的 PR gh-141241 和 gh-152841，了解已有的工作。完成的标准是：一致地删除或澄清不可达的条件代码，且不留下报告中指出的死路径。