Issue #24731: Fixed crash on converting objects with special methods

__bytes__, __trunc__, and __float__ returning instances of subclasses of
bytes, int, and float to subclasses of bytes, int, and float correspondingly.

Lib/test/test_bytes.py

@@ -744,6 +744,14 @@ def __bytes__(self):
             def __index__(self):
                 return 42
         self.assertEqual(bytes(A()), b'a')
+        # Issue #24731
+        class A:
+            def __bytes__(self):
+                return OtherBytesSubclass(b'abc')
+        self.assertEqual(bytes(A()), b'abc')
+        self.assertIs(type(bytes(A())), OtherBytesSubclass)
+        self.assertEqual(BytesSubclass(A()), b'abc')
+        self.assertIs(type(BytesSubclass(A())), BytesSubclass)
 
     # Test PyBytes_FromFormat()
     def test_from_format(self):
@@ -1465,6 +1473,9 @@ class ByteArraySubclass(bytearray):
 class BytesSubclass(bytes):
     pass
 
+class OtherBytesSubclass(bytes):
+    pass
+
 class ByteArraySubclassTest(SubclassTest, unittest.TestCase):
     type2test = bytearray
     subclass2test = ByteArraySubclass

Lib/test/test_float.py

@@ -25,6 +25,12 @@
 test_dir = os.path.dirname(__file__) or os.curdir
 format_testfile = os.path.join(test_dir, 'formatfloat_testcases.txt')
 
+class FloatSubclass(float):
+    pass
+
+class OtherFloatSubclass(float):
+    pass
+
 class GeneralFloatCases(unittest.TestCase):
 
     def test_float(self):
@@ -167,6 +173,15 @@ def __float__(self):
                 return ""
         self.assertRaises(TypeError, time.sleep, Foo5())
 
+        # Issue #24731
+        class F:
+            def __float__(self):
+                return OtherFloatSubclass(42.)
+        self.assertAlmostEqual(float(F()), 42.)
+        self.assertIs(type(float(F())), OtherFloatSubclass)
+        self.assertAlmostEqual(FloatSubclass(F()), 42.)
+        self.assertIs(type(FloatSubclass(F())), FloatSubclass)
+
     def test_is_integer(self):
         self.assertFalse((1.1).is_integer())
         self.assertTrue((1.).is_integer())

Lib/test/test_int.py

@@ -24,6 +24,9 @@
         ("\u0200", ValueError)
 ]
 
+class IntSubclass(int):
+    pass
+
 class IntTestCases(unittest.TestCase):
 
     def test_basic(self):
@@ -441,6 +444,10 @@ def __trunc__(self):
         good_int = TruncReturnsIntSubclass()
         n = int(good_int)
         self.assertEqual(n, 1)
+        self.assertIs(type(n), bool)
+        n = IntSubclass(good_int)
+        self.assertEqual(n, 1)
+        self.assertIs(type(n), IntSubclass)
 
     def test_error_message(self):
         def check(s, base=None):

Lib/test/test_unicode.py

@@ -42,6 +42,9 @@ def duplicate_string(text):
     """
     return text.encode().decode()
 
+class StrSubclass(str):
+    pass
+
 class UnicodeTest(string_tests.CommonTest,
         string_tests.MixinStrUnicodeUserStringTest,
         string_tests.MixinStrUnicodeTest,
@@ -1412,11 +1415,8 @@ def test_constructor(self):
             'unicode remains unicode'
         )
 
-        class UnicodeSubclass(str):
-            pass
-
         for text in ('ascii', '\xe9', '\u20ac', '\U0010FFFF'):
-            subclass = UnicodeSubclass(text)
+            subclass = StrSubclass(text)
             self.assertEqual(str(subclass), text)
             self.assertEqual(len(subclass), len(text))
             if text == 'ascii':
@@ -2169,6 +2169,9 @@ def __str__(self):
         s = str(StrSubclassToStrSubclass("foo"))
         self.assertEqual(s, "foofoo")
         self.assertIs(type(s), StrSubclassToStrSubclass)
+        s = StrSubclass(StrSubclassToStrSubclass("foo"))
+        self.assertEqual(s, "foofoo")
+        self.assertIs(type(s), StrSubclass)
 
     def test_unicode_repr(self):
         class s1:

Misc/NEWS

@@ -10,6 +10,10 @@ Release date: tba
 Core and Builtins
 -----------------
 
+- Issue #24731: Fixed crash on converting objects with special methods
+  __bytes__, __trunc__, and __float__ returning instances of subclasses of
+  bytes, int, and float to subclasses of bytes, int, and float correspondingly.
+
 - Issue #25388: Fixed tokenizer crash when processing undecodable source code
   with a null byte.
 

Objects/bytesobject.c

@@ -2445,7 +2445,7 @@ bytes_methods[] = {
 };
 
 static PyObject *
-str_subtype_new(PyTypeObject *type, PyObject *args, PyObject *kwds);
+bytes_subtype_new(PyTypeObject *type, PyObject *args, PyObject *kwds);
 
 static PyObject *
 bytes_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
@@ -2460,7 +2460,7 @@ bytes_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
     _Py_IDENTIFIER(__bytes__);
 
     if (type != &PyBytes_Type)
-        return str_subtype_new(type, args, kwds);
+        return bytes_subtype_new(type, args, kwds);
     if (!PyArg_ParseTupleAndKeywords(args, kwds, "|Oss:bytes", kwlist, &x,
                                      &encoding, &errors))
         return NULL;
@@ -2687,7 +2687,7 @@ PyBytes_FromObject(PyObject *x)
 }
 
 static PyObject *
-str_subtype_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
+bytes_subtype_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
 {
     PyObject *tmp, *pnew;
     Py_ssize_t n;
@@ -2696,7 +2696,7 @@ str_subtype_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
     tmp = bytes_new(&PyBytes_Type, args, kwds);
     if (tmp == NULL)
         return NULL;
-    assert(PyBytes_CheckExact(tmp));
+    assert(PyBytes_Check(tmp));
     n = PyBytes_GET_SIZE(tmp);
     pnew = type->tp_alloc(type, n);
     if (pnew != NULL) {

Objects/floatobject.c

@@ -1567,7 +1567,7 @@ float_subtype_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
     tmp = float_new(&PyFloat_Type, args, kwds);
     if (tmp == NULL)
         return NULL;
-    assert(PyFloat_CheckExact(tmp));
+    assert(PyFloat_Check(tmp));
     newobj = type->tp_alloc(type, 0);
     if (newobj == NULL) {
         Py_DECREF(tmp);

Objects/longobject.c

@@ -4405,7 +4405,7 @@ long_subtype_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
     tmp = (PyLongObject *)long_new(&PyLong_Type, args, kwds);
     if (tmp == NULL)
         return NULL;
-    assert(PyLong_CheckExact(tmp));
+    assert(PyLong_Check(tmp));
     n = Py_SIZE(tmp);
     if (n < 0)
         n = -n;