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gh-145166: Fix crash in tzinfo.fromutc() when subclass __new__ returns non-datetime #145181

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gh-145166: Fix crash in tzinfo.fromutc() when subclass __new__ returns non-datetime #145181

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13 changes: 12 additions & 1 deletion Lib/_pydatetime.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1348,11 +1348,22 @@ def fromutc(self, dt):
delta = dtoff - dtdst
if delta:
dt += delta
if not isinstance(dt, datetime):
raise TypeError(
f"datetime arithmetic on a subclass returned non-datetime "
f"(type {type(dt).__name__})"
)
dtdst = dt.dst()
if dtdst is None:
raise ValueError("fromutc(): dt.dst gave inconsistent "
"results; cannot convert")
return dt + dtdst
result = dt + dtdst
if not isinstance(result, datetime):
raise TypeError(
f"datetime arithmetic on a subclass returned non-datetime "
f"(type {type(result).__name__})"
)
return result

# Pickle support.

Expand Down
41 changes: 41 additions & 0 deletions Lib/test/datetimetester.py
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Expand Up @@ -5133,6 +5133,47 @@ def test_pickling(self):
self.assertEqual(derived.tzname(), 'cookie')
self.assertEqual(orig.__reduce__(), orig.__reduce_ex__(2))

def test_fromutc_subclass_new_returns_non_datetime(self):
call_count = 0

class EvilDatetime(self.theclass):
def __new__(cls, *args, **kwargs):
nonlocal call_count
call_count += 1
if call_count > 1:
return bytearray(b'\x00' * 200)
return super().__new__(cls, *args, **kwargs)

class SimpleTZ(tzinfo):
def utcoffset(self, dt): return timedelta(hours=1)
def dst(self, dt): return timedelta(hours=1)
def tzname(self, dt): return "Test"

tz = SimpleTZ()
dt = EvilDatetime(2000, 1, 1, 12, 0, 0, tzinfo=tz)
with self.assertRaises(TypeError):
tz.fromutc(dt)

def test_fromutc_subclass_new_returns_non_datetime_with_delta(self):
call_count = 0

class EvilDatetime(self.theclass):
def __new__(cls, *args, **kwargs):
nonlocal call_count
call_count += 1
if call_count > 1:
return bytearray(b'\x00' * 200)
return super().__new__(cls, *args, **kwargs)
class SimpleTZ(tzinfo):
def utcoffset(self, dt): return timedelta(hours=2)
def dst(self, dt): return timedelta(hours=1)
def tzname(self, dt): return "Test"

tz = SimpleTZ()
dt = EvilDatetime(2000, 1, 1, 12, 0, 0, tzinfo=tz)
with self.assertRaises(TypeError):
tz.fromutc(dt)

def test_compat_unpickle(self):
tests = [
b'cdatetime\ndatetime\n'
Expand Down
3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Library/2026-02-24-19-14-43.gh-issue-145166.bG_Rp2.rst
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@@ -0,0 +1,3 @@
Fix crash in :meth:`datetime.tzinfo.fromutc` when a
:class:`~datetime.datetime` subclass ``__new__`` returns a non-datetime
object. A :exc:`TypeError` is now raised instead.
20 changes: 14 additions & 6 deletions Modules/_datetimemodule.c
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Expand Up @@ -4168,7 +4168,6 @@ tzinfo_fromutc(PyObject *self, PyObject *dt)
result = add_datetime_timedelta((PyDateTime_DateTime *)dt, delta, 1);
if (result == NULL)
goto Fail;

Py_DECREF(dst);
dst = call_dst(GET_DT_TZINFO(dt), result);
if (dst == NULL)
Expand Down Expand Up @@ -6210,11 +6209,20 @@ add_datetime_timedelta(PyDateTime_DateTime *date, PyDateTime_Delta *delta,
return NULL;
}

return new_datetime_subclass_ex(year, month, day,
hour, minute, second, microsecond,
HASTZINFO(date) ? date->tzinfo : Py_None,
Py_TYPE(date));
}
PyObject *result = new_datetime_subclass_ex(year, month, day,
hour, minute, second, microsecond,
HASTZINFO(date) ? date->tzinfo : Py_None,
Py_TYPE(date));
if (result != NULL && !PyDateTime_Check(result)) {
PyErr_Format(PyExc_TypeError,
"datetime arithmetic on a subclass returned "
"non-datetime (type %.200s)",
Py_TYPE(result)->tp_name);
Py_DECREF(result);
return NULL;
}
return result;
}

static PyObject *
datetime_add(PyObject *left, PyObject *right)
Expand Down
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