gh-112358: Fix Python 3.12 regression with subclassing struct.Struct. (#112424)

Revert commit c8c0afc7137ab9f22bf59d591084948ca967c97c (PR #94532),
which moved `struct.Struct` initialisation from `Struct.__init__` to `Struct.__new__`.
This caused issues with code in the wild that subclasses `struct.Struct`.

1 files changed, 9 insertions, 14 deletions

diff --git a/Lib/test/test_struct.py b/Lib/test/test_struct.py
index c76649c..15f6ee0 100644
--- a/Lib/test/test_struct.py
+++ b/Lib/test/test_struct.py
@@ -700,20 +700,6 @@ class StructTest(unittest.TestCase):
                 with self.assertRaises(TypeError):
                     cls.x = 1
 
-    @support.cpython_only
-    def test__struct_Struct__new__initialized(self):
-        # See https://github.com/python/cpython/issues/78724
-
-        s = struct.Struct.__new__(struct.Struct, "b")
-        s.unpack_from(b"abcd")
-
-    @support.cpython_only
-    def test__struct_Struct_subclassing(self):
-        class Bob(struct.Struct):
-            pass
-
-        s = Bob("b")
-        s.unpack_from(b"abcd")
 
     def test_issue35714(self):
         # Embedded null characters should not be allowed in format strings.
@@ -774,6 +760,15 @@ class StructTest(unittest.TestCase):
         test_error_propagation('N')
         test_error_propagation('n')
 
+    def test_struct_subclass_instantiation(self):
+        # Regression test for https://github.com/python/cpython/issues/112358
+        class MyStruct(struct.Struct):
+            def __init__(self):
+                super().__init__('>h')
+
+        my_struct = MyStruct()
+        self.assertEqual(my_struct.pack(12345), b'\x30\x39')
+
     def test_repr(self):
         s = struct.Struct('=i2H')
         self.assertEqual(repr(s), f'Struct({s.format!r})')