python · gpshead · Jul 2, 2026
diff --git a/Lib/test/test_int.py b/Lib/test/test_int.py
@@ -732,6 +732,24 @@ def test_int_max_str_digits_is_per_interpreter(self):
             after_value = sys.get_int_max_str_digits()
             self.assertEqual(before_value, after_value)
 
+    def test_int_max_str_digits_not_inherited_by_subinterpreter(self):
+        # gh-98417: sys.set_int_max_str_digits() changes runtime state
+        # only; it must not be written back into the interpreter's
+        # initialization config.  Interpreters created afterwards start
+        # from the initial config, not the current runtime value.
+        sentinel = 99_999
+        if sys.get_int_max_str_digits() == sentinel:
+            sentinel = 88_888
+        code = f"""if 1:
+        import sys
+        if sys.get_int_max_str_digits() == {sentinel}:
+            raise AssertionError(
+                'subinterpreter inherited a runtime limit change')
+        """
+        with support.adjust_int_max_str_digits(sentinel):
+            self.assertEqual(support.run_in_subinterp(code), 0,
+                             'subinterp code failure, check stderr.')
+
 
 class IntSubclassStrDigitLimitsTests(IntStrDigitLimitsTests):
     int_class = IntSubclass

diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2026-07-02-06-15-00.gh-issue-98417.Qk3vXm.rst b/Misc/NEWS.d/next/Core_and_Builtins/2026-07-02-06-15-00.gh-issue-98417.Qk3vXm.rst
@@ -0,0 +1,5 @@
+:func:`sys.set_int_max_str_digits` no longer writes the new limit back into
+the interpreter's initialization configuration (:c:type:`PyConfig`).  As a
+consequence, interpreters created after changing the limit at runtime now
+start with the initial configured limit rather than inheriting the runtime
+value.
@@ -4701,10 +4701,7 @@ _PySys_SetIntMaxStrDigits(int maxdigits)
         return -1;
     }
 
-    // Set PyInterpreterState.long_state.max_str_digits
-    // and PyInterpreterState.config.int_max_str_digits.
     PyInterpreterState *interp = _PyInterpreterState_GET();
     _Py_atomic_store_int(&interp->long_state.max_str_digits, maxdigits);
-    _Py_atomic_store_int(&interp->config.int_max_str_digits, maxdigits);
     return 0;
 }