gh-128335: Make slice generic at runtime

Lib/test/test_genericalias.py

@@ -101,6 +101,7 @@
 class BaseTest(unittest.TestCase):
     """Test basics."""
     generic_types = [type, tuple, list, dict, set, frozenset, enumerate, memoryview,
+                     slice,
                      defaultdict, deque,
                      SequenceMatcher,
                      dircmp,

Misc/NEWS.d/next/Core_and_Builtins/2024-12-29-21-33-08.gh-issue-128334.3c5Nou.rst

@@ -0,0 +1 @@
+Make slice type subscriptable at runtime

Objects/sliceobject.c

@@ -560,6 +560,7 @@ static PyMethodDef slice_methods[] = {
      METH_O,            slice_indices_doc},
     {"__reduce__",      (PyCFunction)slice_reduce,
      METH_NOARGS,       reduce_doc},
+    {"__class_getitem__", Py_GenericAlias, METH_O|METH_CLASS, "See PEP 585"},
     {NULL, NULL}
 };