RustPython · youknowone · May 17, 2026 · May 17, 2026
diff --git a/Lib/test/test_xpickle.py b/Lib/test/test_xpickle.py
@@ -0,0 +1,281 @@
+# This test covers backwards compatibility with previous versions of Python
+# by bouncing pickled objects through Python versions by running xpickle_worker.py.
+import io
+import os
+import pickle
+import struct
+import subprocess
+import sys
+import unittest
+
+
+from test import support
+from test import pickletester
+
+try:
+    import _pickle
+    has_c_implementation = True
+except ModuleNotFoundError:
+    has_c_implementation = False
+
+support.requires('xpickle')
+
+is_windows = sys.platform.startswith('win')
+
+# Map python version to a tuple containing the name of a corresponding valid
+# Python binary to execute and its arguments.
+py_executable_map = {}
+
+protocols_map = {
+    3: (3, 0),
+    4: (3, 4),
+    5: (3, 8),
+}
+
+def highest_proto_for_py_version(py_version):
+    """Finds the highest supported pickle protocol for a given Python version.
+    Args:
+        py_version: a 2-tuple of the major, minor version. Eg. Python 3.7 would
+                    be (3, 7)
+    Returns:
+        int for the highest supported pickle protocol
+    """
+    proto = 2
+    for p, v in protocols_map.items():
+        if py_version < v:
+            break
+        proto = p
+    return proto
+
+def have_python_version(py_version):
+    """Check whether a Python binary exists for the given py_version and has
+    support. This respects your PATH.
+    For Windows, it will first try to use the py launcher specified in PEP 397.
+    Otherwise (and for all other platforms), it will attempt to check for
+    python<py_version[0]>.<py_version[1]>.
+
+    Eg. given a *py_version* of (3, 7), the function will attempt to try
+    'py -3.7' (for Windows) first, then 'python3.7', and return
+    ['py', '-3.7'] (on Windows) or ['python3.7'] on other platforms.
+
+    Args:
+        py_version: a 2-tuple of the major, minor version. Eg. python 3.7 would
+                    be (3, 7)
+    Returns:
+        List/Tuple containing the Python binary name and its required arguments,
+        or None if no valid binary names found.
+    """
+    python_str = ".".join(map(str, py_version))
+    targets = [('py', f'-{python_str}'), (f'python{python_str}',)]
+    if py_version not in py_executable_map:
+        for target in targets[0 if is_windows else 1:]:
+            try:
+                worker = subprocess.Popen([*target, '-c', 'pass'],
+                                          stdout=subprocess.DEVNULL,
+                                          stderr=subprocess.DEVNULL,
+                                          shell=is_windows)
+                worker.communicate()
+                if worker.returncode == 0:
+                    py_executable_map[py_version] = target
+                break
+            except FileNotFoundError:
+                pass
+
+    return py_executable_map.get(py_version, None)
+
+
+def read_exact(f, n):
+    buf = b''
+    while len(buf) < n:
+        chunk = f.read(n - len(buf))
+        if not chunk:
+            raise EOFError
+        buf += chunk
+    return buf
+
+
+class AbstractCompatTests(pickletester.AbstractPickleTests):
+    py_version = None
+    worker = None
+
+    @classmethod
+    def setUpClass(cls):
+        assert cls.py_version is not None, 'Needs a python version tuple'
+        if not have_python_version(cls.py_version):
+            py_version_str = ".".join(map(str, cls.py_version))
+            raise unittest.SkipTest(f'Python {py_version_str} not available')
+        cls.addClassCleanup(cls.finish_worker)
+        # Override the default pickle protocol to match what xpickle worker
+        # will be running.
+        highest_protocol = highest_proto_for_py_version(cls.py_version)
+        cls.enterClassContext(support.swap_attr(pickletester, 'protocols',
+                                                range(highest_protocol + 1)))
+        cls.enterClassContext(support.swap_attr(pickle, 'HIGHEST_PROTOCOL',
+                                                highest_protocol))
+
+    @classmethod
+    def start_worker(cls, python):
+        target = os.path.join(os.path.dirname(__file__), 'xpickle_worker.py')
+        worker = subprocess.Popen([*python, target],
+                                  stdin=subprocess.PIPE,
+                                  stdout=subprocess.PIPE,
+                                  stderr=subprocess.PIPE,
+                                  # For windows bpo-17023.
+                                  shell=is_windows)
+        cls.worker = worker
+        return worker
+
+    @classmethod
+    def finish_worker(cls):
+        worker = cls.worker
+        if worker is None:
+            return
+        cls.worker = None
+        worker.stdin.close()
+        worker.stdout.close()
+        worker.stderr.close()
+        worker.terminate()
+        worker.wait()
+
+    @classmethod
+    def send_to_worker(cls, python, data):
+        """Bounce a pickled object through another version of Python.
+        This will send data to a child process where it will
+        be unpickled, then repickled and sent back to the parent process.
+        Args:
+            python: list containing the python binary to start and its arguments
+            data: bytes object to send to the child process
+        Returns:
+            The pickled data received from the child process.
+        """
+        worker = cls.worker
+        if worker is None:
+            worker = cls.start_worker(python)
+
+        try:
+            worker.stdin.write(struct.pack('!i', len(data)) + data)
+            worker.stdin.flush()
+
+            size, = struct.unpack('!i', read_exact(worker.stdout, 4))
+            if size > 0:
+                return read_exact(worker.stdout, size)
+            # if the worker fails, it will write the exception to stdout
+            if size < 0:
+                stdout = read_exact(worker.stdout, -size)
+                try:
+                    exception = pickle.loads(stdout)
+                except (pickle.UnpicklingError, EOFError):
+                    pass
+                else:
+                    if isinstance(exception, Exception):
+                        # To allow for tests which test for errors.
+                        raise exception
+            _, stderr = worker.communicate()
+            raise RuntimeError(stderr)
+        except:
+            cls.finish_worker()
+            raise
+
+    def dumps(self, arg, proto=0, **kwargs):
+        # Skip tests that require buffer_callback arguments since
+        # there isn't a reliable way to marshal/pickle the callback and ensure
+        # it works in a different Python version.
+        if 'buffer_callback' in kwargs:
+            self.skipTest('Test does not support "buffer_callback" argument.')
+        f = io.BytesIO()
+        p = self.pickler(f, proto, **kwargs)
+        p.dump(arg)
+        data = struct.pack('!i', proto) + f.getvalue()
+        python = py_executable_map[self.py_version]
+        return self.send_to_worker(python, data)
+
+    def loads(self, buf, **kwds):
+        f = io.BytesIO(buf)
+        u = self.unpickler(f, **kwds)
+        return u.load()
+
+    # A scaled-down version of test_bytes from pickletester, to reduce
+    # the number of calls to self.dumps() and hence reduce the number of
+    # child python processes forked. This allows the test to complete
+    # much faster (the one from pickletester takes 3-4 minutes when running
+    # under text_xpickle).
+    def test_bytes(self):
+        if self.py_version < (3, 0):
+            self.skipTest('not supported in Python < 3.0')
+        for proto in pickletester.protocols:
+            for s in b'', b'xyz', b'xyz'*100:
+                p = self.dumps(s, proto)
+                self.assert_is_copy(s, self.loads(p))
+            s = bytes(range(256))
+            p = self.dumps(s, proto)
+            self.assert_is_copy(s, self.loads(p))
+            s = bytes([i for i in range(256) for _ in range(2)])
+            p = self.dumps(s, proto)
+            self.assert_is_copy(s, self.loads(p))
+
+    # These tests are disabled because they require some special setup
+    # on the worker that's hard to keep in sync.
+    test_global_ext1 = None
+    test_global_ext2 = None
+    test_global_ext4 = None
+
+    # These tests fail because they require classes from pickletester
+    # which cannot be properly imported by the xpickle worker.
+    test_recursive_nested_names = None
+    test_recursive_nested_names2 = None
+
+    # Attribute lookup problems are expected, disable the test
+    test_dynamic_class = None
+    test_evil_class_mutating_dict = None
+
+    # Expected exception is raised during unpickling in a subprocess.
+    test_pickle_setstate_None = None
+
+    # Other Python version may not have NumPy.
+    test_buffers_numpy = None
+
+    # Skip tests that require buffer_callback arguments since
+    # there isn't a reliable way to marshal/pickle the callback and ensure
+    # it works in a different Python version.
+    test_in_band_buffers = None
+    test_buffers_error = None
+    test_oob_buffers = None
+    test_oob_buffers_writable_to_readonly = None
+
+class PyPicklePythonCompat(AbstractCompatTests):
+    pickler = pickle._Pickler
+    unpickler = pickle._Unpickler
+
+if has_c_implementation:
+    class CPicklePythonCompat(AbstractCompatTests):
+        pickler = _pickle.Pickler
+        unpickler = _pickle.Unpickler
+
+
+def make_test(py_version, base):
+    class_dict = {'py_version': py_version}
+    name = base.__name__.replace('Python', 'Python%d%d' % py_version)
+    return type(name, (base, unittest.TestCase), class_dict)
+
+def load_tests(loader, tests, pattern):
+    def add_tests(py_version):
+        test_class = make_test(py_version, PyPicklePythonCompat)
+        tests.addTest(loader.loadTestsFromTestCase(test_class))
+        if has_c_implementation:
+            test_class = make_test(py_version, CPicklePythonCompat)
+            tests.addTest(loader.loadTestsFromTestCase(test_class))
+
+    value = support.get_resource_value('xpickle')
+    if value is None:
+        major = sys.version_info.major
+        assert major == 3
+        add_tests((2, 7))
+        for minor in range(2, sys.version_info.minor):
+            add_tests((major, minor))
+    else:
+        add_tests(tuple(map(int, value.split('.'))))
+    return tests
+
+
+if __name__ == '__main__':
+    unittest.main()
diff --git a/Lib/test/xpickle_worker.py b/Lib/test/xpickle_worker.py
@@ -0,0 +1,62 @@
+# This script is called by test_xpickle as a subprocess to load and dump
+# pickles in a different Python version.
+import os
+import pickle
+import struct
+import sys
+
+
+# This allows the xpickle worker to import picklecommon.py, which it needs
+# since some of the pickle objects hold references to picklecommon.py.
+test_mod_path = os.path.abspath(os.path.join(os.path.dirname(__file__),
+                                             'picklecommon.py'))
+if sys.version_info >= (3, 5):
+    import importlib.util
+    spec = importlib.util.spec_from_file_location('test.picklecommon', test_mod_path)
+    sys.modules['test'] = type(sys)('test')
+    test_module = importlib.util.module_from_spec(spec)
+    spec.loader.exec_module(test_module)
+    sys.modules['test.picklecommon'] = test_module
+else:
+    test_module = type(sys)('test.picklecommon')
+    sys.modules['test.picklecommon'] = test_module
+    sys.modules['test'] = type(sys)('test')
+    with open(test_mod_path, 'rb') as f:
+        sources = f.read()
+    exec(sources, vars(test_module))
+
+def read_exact(f, n):
+    buf = b''
+    while len(buf) < n:
+        chunk = f.read(n - len(buf))
+        if not chunk:
+            raise EOFError
+        buf += chunk
+    return buf
+
+in_stream = getattr(sys.stdin, 'buffer', sys.stdin)
+out_stream = getattr(sys.stdout, 'buffer', sys.stdout)
+
+try:
+    while True:
+        size, = struct.unpack('!i', read_exact(in_stream, 4))
+        if not size:
+            break
+        data = read_exact(in_stream, size)
+        protocol, = struct.unpack('!i', data[:4])
+        obj = pickle.loads(data[4:])
+        data = pickle.dumps(obj, protocol)
+        out_stream.write(struct.pack('!i', len(data)) + data)
+        out_stream.flush()
+except Exception as exc:
+    # dump the exception to stdout and write to stderr, then exit
+    try:
+        data = pickle.dumps(exc)
+        out_stream.write(struct.pack('!i', -len(data)) + data)
+        out_stream.flush()
+    except Exception:
+        out_stream.write(struct.pack('!i', 0))
+        out_stream.flush()
+        sys.stderr.write(repr(exc))
+        sys.stderr.flush()
+    sys.exit(1)
diff --git a/scripts/update_lib/deps.py b/scripts/update_lib/deps.py
@@ -320,10 +320,12 @@ def clear_import_graph_caches() -> None:
     "pickle": {
         "hard_deps": ["_compat_pickle.py"],
         "test": [
+            "picklecommon.py",
             "test_pickle.py",
             "test_picklebuffer.py",
             "test_pickletools.py",
-            "picklecommon.py",
+            "test_xpickle.py",
+            "xpickle_worker.py",
         ],
     },
     "re": {