https://github.com/python/cpython/commit/3a1b5473f217fc493f743c9ca8b877d2e76f8e6b
commit: 3a1b5473f217fc493f743c9ca8b877d2e76f8e6b
branch: main
author: Serhiy Storchaka <[email protected]>
committer: serhiy-storchaka <[email protected]>
date: 2026-07-06T21:10:23+03:00
summary:
gh-153200: Fix math.isqrt() for int subclasses with overridden comparison
operators (GH-153203)
The final check-and-correct comparison in the arbitrary precision path
could call a comparison operator overridden in an int subclass.
Compare by value with int's tp_richcompare.
files:
A Misc/NEWS.d/next/Library/2026-07-06-12-00-00.gh-issue-153200.isqrtLt.rst
M Lib/test/test_math_integer.py
M Modules/mathintegermodule.c
diff --git a/Lib/test/test_math_integer.py b/Lib/test/test_math_integer.py
index 09a98d93bd636c..d1bc776dc42391 100644
--- a/Lib/test/test_math_integer.py
+++ b/Lib/test/test_math_integer.py
@@ -15,6 +15,19 @@ def __init__(self, value):
def __index__(self):
return self.value
+# int subclass with broken arithmetic operators; implementations must
+# convert their arguments to exact ints instead of using these.
+class BadIntSubclass(int):
+ def _binop(self, other='ignored', mod=None):
+ return 42
+ __add__ = __radd__ = __sub__ = __rsub__ = _binop
+ __mul__ = __rmul__ = __mod__ = __rmod__ = _binop
+ __divmod__ = __rdivmod__ = __pow__ = __rpow__ = _binop
+ __floordiv__ = __rfloordiv__ = _binop
+ __lshift__ = __rlshift__ = __rshift__ = __rrshift__ = _binop
+ __and__ = __rand__ = __or__ = __ror__ = __xor__ = __rxor__ = _binop
+ __lt__ = __le__ = __gt__ = __ge__ = _binop
+
# Here's a pure Python version of the math.integer.factorial algorithm, for
# documentation and comparison purposes.
#
@@ -226,6 +239,11 @@ def test_isqrt(self):
self.assertIntEqual(isqrt(False), 0)
self.assertIntEqual(isqrt(MyIndexable(1729)), 41)
+ # Overridden operators of an int subclass must not affect the
+ # result.
+ self.assertIntEqual(isqrt(BadIntSubclass(10**20)), 10**10)
+ self.assertIntEqual(isqrt(BadIntSubclass(10**20 - 1)), 10**10 - 1)
+
with self.assertRaises(ValueError):
isqrt(MyIndexable(-3))
diff --git
a/Misc/NEWS.d/next/Library/2026-07-06-12-00-00.gh-issue-153200.isqrtLt.rst
b/Misc/NEWS.d/next/Library/2026-07-06-12-00-00.gh-issue-153200.isqrtLt.rst
new file mode 100644
index 00000000000000..a27ac73fe31a70
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-07-06-12-00-00.gh-issue-153200.isqrtLt.rst
@@ -0,0 +1,3 @@
+Fix :func:`math.isqrt` returning an incorrect result for arguments not
+less than 2**64 that are instances of an :class:`int` subclass with an
+overridden comparison operator.
diff --git a/Modules/mathintegermodule.c b/Modules/mathintegermodule.c
index cfad4154b2d361..0f660d461e349f 100644
--- a/Modules/mathintegermodule.c
+++ b/Modules/mathintegermodule.c
@@ -454,16 +454,20 @@ math_integer_isqrt(PyObject *module, PyObject *n)
/* The correct result is either a or a - 1. Figure out which, and
decrement a if necessary. */
- /* a_too_large = n < a * a */
+ /* a_too_large = n < a * a. Compare by value: n can be an instance
+ of an int subclass with an overridden __lt__ method. */
b = PyNumber_Multiply(a, a);
if (b == NULL) {
goto error;
}
- a_too_large = PyObject_RichCompareBool(n, b, Py_LT);
+ PyObject *cmp = PyLong_Type.tp_richcompare(n, b, Py_LT);
Py_DECREF(b);
- if (a_too_large == -1) {
+ if (cmp == NULL) {
goto error;
}
+ assert(PyBool_Check(cmp));
+ a_too_large = (cmp == Py_True);
+ Py_DECREF(cmp);
if (a_too_large) {
Py_SETREF(a, PyNumber_Subtract(a, _PyLong_GetOne()));
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