gh-156865: don't raise exceptions for overflows in the ctypes module

Author: skirpichev

Lib/test/test_ctypes/test_numbers.py

@@ -240,6 +240,21 @@ 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'))
+        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()

Misc/NEWS.d/next/Library/2026-09-04-11-45-08.gh-issue-156865.mrdfKJ.rst

@@ -0,0 +1,2 @@
+Don't raise exceptions on overflows in floating-point types of the
+:mod:`ctypes`.  Patch by Sergey B Kirpichev.

Modules/_ctypes/cfield.c

@@ -865,14 +865,14 @@ Zf_set_sw(void *ptr, PyObject *value, Py_ssize_t size)
         return NULL;
     }
 #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))
     {
         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;
     }