fix: Explicitly disallow _as_parameter_ returning tuples for default conversions in ctypes and add a test for the TypeError it raises.

Author: CodeMaverick-143

Lib/test/test_ctypes/test_parameters.py

@@ -297,6 +297,20 @@ def from_param(cls, value):
 
         self.assertEqual(trace, [1, 2, 3, 4, 5])
 
+    def test_as_parameter_tuple(self):
+        class Dangerous(object):
+            @property
+            def _as_parameter_(self):
+                return ('i', 42)
+
+        func = CDLL(_ctypes_test.__file__)._testfunc_p_p
+        func.restype = c_int
+        # func.argtypes = [c_void_p]  # Do not set argtypes to force default conversion
+
+        # Should raise TypeError because tuples are not supported in default conversion
+        with self.assertRaisesRegex(TypeError, "Don't know how to convert parameter 1"):
+            func(Dangerous(), 0)
+
 
 if __name__ == '__main__':
     unittest.main()

Modules/_ctypes/callproc.c

@@ -620,9 +620,6 @@ PyType_Spec carg_spec = {
  *    by value, or a 2-tuple or 3-tuple which will be used according
  *    to point 2 above. The third item (if any), is ignored. It is normally
  *    used to keep the object alive where this parameter refers to.
- *    XXX This convention is dangerous - you can construct arbitrary tuples
- *    in Python and pass them. Would it be safer to use a custom container
- *    datatype instead of a tuple?
  *
  * 4. Other Python objects cannot be passed as parameters - an exception is raised.
  *