Issue #24164: Objects that need calling ``__new__`` with keyword arguments,

can now be pickled using pickle protocols older than protocol version 4.

2 files changed, 14 insertions, 9 deletions

diff --git a/Lib/pickle.py b/Lib/pickle.py
index e93057a..d41753d 100644
--- a/Lib/pickle.py
+++ b/Lib/pickle.py
@@ -27,6 +27,7 @@ from types import FunctionType
 from copyreg import dispatch_table
 from copyreg import _extension_registry, _inverted_registry, _extension_cache
 from itertools import islice
+from functools import partial
 import sys
 from sys import maxsize
 from struct import pack, unpack
@@ -544,7 +545,7 @@ class _Pickler:
         write = self.write
 
         func_name = getattr(func, "__name__", "")
-        if self.proto >= 4 and func_name == "__newobj_ex__":
+        if self.proto >= 2 and func_name == "__newobj_ex__":
             cls, args, kwargs = args
             if not hasattr(cls, "__new__"):
                 raise PicklingError("args[0] from {} args has no __new__"
@@ -552,10 +553,16 @@ class _Pickler:
             if obj is not None and cls is not obj.__class__:
                 raise PicklingError("args[0] from {} args has the wrong class"
                                     .format(func_name))
-            save(cls)
-            save(args)
-            save(kwargs)
-            write(NEWOBJ_EX)
+            if self.proto >= 4:
+                save(cls)
+                save(args)
+                save(kwargs)
+                write(NEWOBJ_EX)
+            else:
+                func = partial(cls.__new__, cls, *args, **kwargs)
+                save(func)
+                save(())
+                write(REDUCE)
         elif self.proto >= 2 and func_name == "__newobj__":
             # A __reduce__ implementation can direct protocol 2 or newer to
             # use the more efficient NEWOBJ opcode, while still
diff --git a/Lib/test/pickletester.py b/Lib/test/pickletester.py
index 2ef48e6..fd641e3 100644
--- a/Lib/test/pickletester.py
+++ b/Lib/test/pickletester.py
@@ -1580,16 +1580,14 @@ class AbstractPickleTests(unittest.TestCase):
         x.abc = 666
         for proto in protocols:
             with self.subTest(proto=proto):
-                if 2 <= proto < 4:
-                    self.assertRaises(ValueError, self.dumps, x, proto)
-                    continue
                 s = self.dumps(x, proto)
                 if proto < 1:
                     self.assertIn(b'\nL64206', s)  # LONG
                 elif proto < 2:
                     self.assertIn(b'M\xce\xfa', s)  # BININT2
+                elif proto < 4:
+                    self.assertIn(b'X\x04\x00\x00\x00FACE', s)  # BINUNICODE
                 else:
-                    assert proto >= 4
                     self.assertIn(b'\x8c\x04FACE', s)  # SHORT_BINUNICODE
                 self.assertFalse(opcode_in_pickle(pickle.NEWOBJ, s))
                 self.assertEqual(opcode_in_pickle(pickle.NEWOBJ_EX, s),