https://github.com/python/cpython/commit/3f33bf83e8496737b86333bc9ec55dc3ccb3faca
commit: 3f33bf83e8496737b86333bc9ec55dc3ccb3faca
branch: main
author: Serhiy Storchaka <[email protected]>
committer: serhiy-storchaka <[email protected]>
date: 2026-03-10T18:29:23+02:00
summary:
gh-145743: Fix inconsistency after calling Struct.__init__() with invalid
format (GH-145744)
Only set the format attribute after successful (re-)initialization.
files:
M Lib/test/test_struct.py
M Modules/_struct.c
diff --git a/Lib/test/test_struct.py b/Lib/test/test_struct.py
index 4cbfd7ad8b1e48..6904572d095d31 100644
--- a/Lib/test/test_struct.py
+++ b/Lib/test/test_struct.py
@@ -584,8 +584,24 @@ def test_Struct_reinitialization(self):
# Issue 9422: there was a memory leak when reinitializing a
# Struct instance. This test can be used to detect the leak
# when running with regrtest -L.
- s = struct.Struct('i')
- s.__init__('ii')
+ s = struct.Struct('>h')
+ s.__init__('>hh')
+ self.assertEqual(s.format, '>hh')
+ packed = b'\x00\x01\x00\x02'
+ self.assertEqual(s.pack(1, 2), packed)
+ self.assertEqual(s.unpack(packed), (1, 2))
+
+ with self.assertRaises(UnicodeEncodeError):
+ s.__init__('\udc00')
+ self.assertEqual(s.format, '>hh')
+ self.assertEqual(s.pack(1, 2), packed)
+ self.assertEqual(s.unpack(packed), (1, 2))
+
+ with self.assertRaises(struct.error):
+ s.__init__('$')
+ self.assertEqual(s.format, '>hh')
+ self.assertEqual(s.pack(1, 2), packed)
+ self.assertEqual(s.unpack(packed), (1, 2))
def check_sizeof(self, format_str, number_of_codes):
# The size of 'PyStructObject'
diff --git a/Modules/_struct.c b/Modules/_struct.c
index dcc3c7ec63e9e0..c2f7b1fe0e800a 100644
--- a/Modules/_struct.c
+++ b/Modules/_struct.c
@@ -1620,11 +1620,11 @@ align(Py_ssize_t size, char c, const formatdef *e)
/* calculate the size of a format string */
static int
-prepare_s(PyStructObject *self)
+prepare_s(PyStructObject *self, PyObject *format)
{
const formatdef *f;
const formatdef *e;
- formatcode *codes;
+ formatcode *codes, *codes0;
const char *s;
const char *fmt;
@@ -1634,8 +1634,8 @@ prepare_s(PyStructObject *self)
_structmodulestate *state = get_struct_state_structinst(self);
- fmt = PyBytes_AS_STRING(self->s_format);
- if (strlen(fmt) != (size_t)PyBytes_GET_SIZE(self->s_format)) {
+ fmt = PyBytes_AS_STRING(format);
+ if (strlen(fmt) != (size_t)PyBytes_GET_SIZE(format)) {
PyErr_SetString(state->StructError,
"embedded null character");
return -1;
@@ -1711,13 +1711,7 @@ prepare_s(PyStructObject *self)
PyErr_NoMemory();
return -1;
}
- /* Free any s_codes value left over from a previous initialization. */
- if (self->s_codes != NULL)
- PyMem_Free(self->s_codes);
- self->s_codes = codes;
- self->s_size = size;
- self->s_len = len;
-
+ codes0 = codes;
s = fmt;
size = 0;
while ((c = *s++) != '\0') {
@@ -1757,6 +1751,14 @@ prepare_s(PyStructObject *self)
codes->size = 0;
codes->repeat = 0;
+ /* Free any s_codes value left over from a previous initialization. */
+ if (self->s_codes != NULL)
+ PyMem_Free(self->s_codes);
+ self->s_codes = codes0;
+ self->s_size = size;
+ self->s_len = len;
+ Py_XSETREF(self->s_format, Py_NewRef(format));
+
return 0;
overflow:
@@ -1820,9 +1822,8 @@ Struct___init___impl(PyStructObject *self, PyObject
*format)
return -1;
}
- Py_SETREF(self->s_format, format);
-
- ret = prepare_s(self);
+ ret = prepare_s(self, format);
+ Py_DECREF(format);
return ret;
}
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