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gh-98417: Stop modifying PyConfig in sys.set_int_max_str_digits() #152869

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gh-98417: Stop modifying PyConfig in sys.set_int_max_str_digits() #152869

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gh-98417: Stop modifying PyConfig in sys.set_int_max_str_digits() 
PyConfig is an input to interpreter initialization; the copy stored on
PyInterpreterState records how the interpreter was initialized.  The
runtime int<->str digit limit already lives in
PyInterpreterState.long_state.max_str_digits and that is what all
readers use, so drop the write-back into
interp->config.int_max_str_digits from _PySys_SetIntMaxStrDigits().

As a consequence, interpreters created after a runtime limit change now
start from the initially-configured limit instead of inheriting the
current runtime value.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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@gpshead @claude
gpshead and claude committed Jul 2, 2026
commit 967527448b77d3e2f6080ae0d741067787378d82
18 changes: 18 additions & 0 deletions Lib/test/test_int.py
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Original file line number Diff line number Diff line change
Expand Up @@ -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
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5 changes: 5 additions & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2026-07-02-06-15-00.gh-issue-98417.Qk3vXm.rst
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@@ -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.
3 changes: 0 additions & 3 deletions Python/sysmodule.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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;
}
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