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gh-144100: Fix crash for POINTER(str) used in ctypes argtypes #144108

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Merged
vstinner merged 7 commits into from
Jan 26, 2026
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gh-144100: Fix crash for POINTER(str) used in ctypes argtypes #144108

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gh-144100: Fix crash for POINTER(str) used in ctypes argtypes
VanshAgarwal24036 Jan 21, 2026
bda7921
Test corrected
VanshAgarwal24036 Jan 21, 2026
1685958
Update Modules/_ctypes/_ctypes.c
VanshAgarwal24036 Jan 23, 2026
5587067
Update Modules/_ctypes/_ctypes.c
VanshAgarwal24036 Jan 23, 2026
e948a1a
Update test file
VanshAgarwal24036 Jan 23, 2026
8a05d9e
Update test file
VanshAgarwal24036 Jan 23, 2026
138e52d
Fx error fail
VanshAgarwal24036 Jan 23, 2026
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18 changes: 18 additions & 0 deletions Lib/test/test_ctypes/test_pointers.py
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Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,7 @@
import gc
import sys
import unittest
import os
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@vstinner vstinner Jan 23, 2026

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This import can be removed with my proposed code.

from ctypes import (CDLL, CFUNCTYPE, Structure,
POINTER, pointer, _Pointer,
byref, sizeof,
Expand Down Expand Up @@ -472,6 +473,23 @@ class C(Structure):
ptr.set_type(c_int)
self.assertIs(ptr._type_, c_int)

class TestPointerStringProto(unittest.TestCase):
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@vstinner vstinner Jan 23, 2026

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I would prefer to add the test to the end of PointersTestCase, instead of adding a new test case.

def test_pointer_string_proto_argtypes_error(self):
with self.assertWarns(DeprecationWarning):
BadType = ctypes.POINTER("BugTrigger")
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@vstinner vstinner Jan 23, 2026

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I would prefer to avoid deprecated code path. You should be able to use:

Suggested change
with self.assertWarns(DeprecationWarning):
BadType = ctypes.POINTER("BugTrigger")
class BadType(ctypes._Pointer):
# _type_ is not defined on purpose
pass


if os.name == "nt":
libc = ctypes.WinDLL("kernel32.dll")
func = libc.GetCurrentProcessId
else:
libc = ctypes.CDLL(None)
func = libc.getpid

func.argtypes = (BadType,)
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@vstinner vstinner Jan 23, 2026

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You can use the Python C API:

Suggested change
if os.name == "nt":
libc = ctypes.WinDLL("kernel32.dll")
func = libc.GetCurrentProcessId
else:
libc = ctypes.CDLL(None)
func = libc.getpid
func.argtypes = (BadType,)
func = ctypes.pythonapi.Py_GetVersion
func.argtypes = (BadType,)


with self.assertRaises(ctypes.ArgumentError):
func(ctypes.byref(ctypes.c_int(0)))


if __name__ == '__main__':
unittest.main()
3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Library/2026-01-21-19-39-07.gh-issue-144100.hLMZ8Y.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
Fixed a crash in ctypes when using a deprecated ``POINTER(str)`` type in
``argtypes``. Instead of aborting, ctypes now raises a proper Python
exception when the pointer target type is unresolved.
8 changes: 7 additions & 1 deletion Modules/_ctypes/_ctypes.c
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Expand Up @@ -1419,7 +1419,13 @@ PyCPointerType_from_param_impl(PyObject *type, PyTypeObject *cls,
/* If we expect POINTER(<type>), but receive a <type> instance, accept
it by calling byref(<type>).
*/
assert(typeinfo->proto);
if(typeinfo->proto == NULL){
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PyErr_SetString(
PyExc_TypeError,
"cannot convert argument: POINTER target type is unresolved"
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);
return NULL;
}
switch (PyObject_IsInstance(value, typeinfo->proto)) {
case 1:
Py_INCREF(value); /* _byref steals a refcount */
Expand Down
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