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gh-156865: Don't raise exceptions for ctypes.c_float_complex overflows #156919

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gh-156865: Don't raise exceptions for ctypes.c_float_complex overflows #156919

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ca96502
gh-156865: don't raise exceptions for overflows in the ctypes module
skirpichev Sep 4, 2026
bb3fd9e
skip that for poor childrens
skirpichev Sep 4, 2026
e7afd4e
Merge branch 'main' into fix-ctypes-Zf_set_sw
skirpichev Sep 4, 2026
309d8f3
Update Misc/NEWS.d/next/Library/2026-09-04-11-45-08.gh-issue-156865.m…
skirpichev Sep 18, 2026
bdfb931
Merge branch 'master' into fix-ctypes-Zf_set_sw
skirpichev Sep 18, 2026
c00602e
address review: split tests
skirpichev Sep 18, 2026
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20 changes: 20 additions & 0 deletions Lib/test/test_ctypes/test_numbers.py
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Original file line number Diff line number Diff line change
Expand Up @@ -240,6 +240,26 @@ def test_float_overflow(self):
if (hasattr(t, "__ctype_le__")):
self.assertRaises(OverflowError, t.__ctype_le__, big_int)

# gh-156865: be silent in overflows of C types
self.assertEqual(ctypes.c_float(3e300).value, float('inf'))
self.assertEqual(ctypes.c_float.__ctype_le__(3e300).value, float('inf'))
self.assertEqual(ctypes.c_float.__ctype_be__(3e300).value, float('inf'))

@unittest.skipUnless(hasattr(ctypes, "c_float_complex"),
"requires C11 complex type")
def test_complex_overflow(self):
# gh-156865: be silent in overflows of C types
self.assertEqual(ctypes.c_float_complex(3e300).value, complex('inf'))
self.assertEqual(ctypes.c_float_complex.__ctype_le__(3e300).value,
complex('inf'))
self.assertEqual(ctypes.c_float_complex.__ctype_be__(3e300).value,
complex('inf'))
self.assertEqual(ctypes.c_float_complex(3e300j).value, complex('infj'))
self.assertEqual(ctypes.c_float_complex.__ctype_le__(3e300j).value,
complex('infj'))
self.assertEqual(ctypes.c_float_complex.__ctype_be__(3e300j).value,
complex('infj'))


if __name__ == '__main__':
unittest.main()
2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2026-09-04-11-45-08.gh-issue-156865.mrdfKJ.rst
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@@ -0,0 +1,2 @@
:mod:`ctypes`: Don't raise exceptions on overflows in floating-point types.

@vstinner vstinner Sep 23, 2026

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If I understand the change correctly, only ctypes.c_float_complex is affected. So I suggest to mention the type directly:

Suggested change
:mod:`ctypes`: Don't raise exceptions on overflows in floating-point types.
Don't raise exceptions on overflows in :class:`ctypes.c_float_complex`.

Patch by Sergey B Kirpichev.
8 changes: 4 additions & 4 deletions Modules/_ctypes/cfield.c
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Expand Up @@ -865,14 +865,14 @@ Zf_set_sw(void *ptr, PyObject *value, Py_ssize_t size)
return NULL;
}
#ifdef WORDS_BIGENDIAN

@vstinner vstinner Sep 23, 2026

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The purpose of the casts is not obvious to me. IMO it's worth it to add a comment to explain they.

Suggested change
#ifdef WORDS_BIGENDIAN
// gh-156865: Cast double to float to avoid overflow in PyFloat_Pack4()
#ifdef WORDS_BIGENDIAN

if (PyFloat_Pack4(c.real, ptr, 1)
|| PyFloat_Pack4(c.imag, ptr + sizeof(float), 1))
if (PyFloat_Pack4((float)c.real, ptr, 1)
|| PyFloat_Pack4((float)c.imag, ptr + sizeof(float), 1))
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{
return NULL;
}
#else
if (PyFloat_Pack4(c.real, ptr, 0)
|| PyFloat_Pack4(c.imag, ptr + sizeof(float), 0))
if (PyFloat_Pack4((float)c.real, ptr, 0)
|| PyFloat_Pack4((float)c.imag, ptr + sizeof(float), 0))
{
return NULL;
}
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