Issue #21951: Fixed a crash in Tkinter on AIX when called Tcl command with

empty string or tuple argument.

On some platforms Tcl memory allocator returns NULL when allocating zero-sized
block of memory.

Lib/test/test_tcl.py

@@ -418,7 +418,6 @@ class TclTest(unittest.TestCase):
         self.assertEqual(passValue(['a', ['b', 'c']]),
                          ('a', ('b', 'c')) if self.wantobjects else 'a {b c}')
 
-    @unittest.skipIf(sys.platform.startswith("aix"), 'Issue #21951: crashes on AIX')
     def test_user_command(self):
         result = None
         def testfunc(arg):
@@ -446,9 +445,11 @@ class TclTest(unittest.TestCase):
         check('string')
         check('string\xbd')
         check('string\u20ac')
+        check('')
         check(b'string', 'string')
         check(b'string\xe2\x82\xac', 'string\xe2\x82\xac')
         check(b'string\xbd', 'string\xbd')
+        check(b'', '')
         check('str\x00ing')
         check('str\x00ing\xbd')
         check('str\x00ing\u20ac')

Misc/NEWS

@@ -132,6 +132,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #21951: Fixed a crash in Tkinter on AIX when called Tcl command with
+  empty string or tuple argument.
+
 - Issue #21951: Tkinter now most likely raises MemoryError instead of crash
   if the memory allocation fails.
 

Modules/_tkinter.c

@@ -906,6 +906,8 @@ AsObj(PyObject *value)
         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" :
@@ -936,6 +938,8 @@ AsObj(PyObject *value)
 
         inbuf = PyUnicode_DATA(value);
         size = PyUnicode_GET_LENGTH(value);
+        if (size == 0)
+            return Tcl_NewUnicodeObj((const void *)"", 0);
         if (!CHECK_SIZE(size, sizeof(Tcl_UniChar))) {
             PyErr_SetString(PyExc_OverflowError, "string is too long");
             return NULL;