Support pickling cached_property descriptors on Python 3.8-3.11

CHANGES.md

@@ -1,6 +1,9 @@
 In development
 ==============
 
+- Support pickling `functools.cached_property` descriptors on Python 3.8-3.11.
+  ([issue #438](https://github.com/cloudpipe/cloudpickle/issues/438))
+
 - Make pickling of functions depending on globals in notebook more
   deterministic. ([PR#560](https://github.com/cloudpipe/cloudpickle/pull/560))
 

cloudpickle/cloudpickle.py

@@ -58,6 +58,7 @@
 import dataclasses
 import dis
 from enum import Enum
+import functools
 import io
 import itertools
 import logging
@@ -1049,6 +1050,15 @@ def _property_reduce(obj):
     return property, (obj.fget, obj.fset, obj.fdel, obj.__doc__)
 
 
+def _cached_property_reduce(obj):
+    # Recreate the descriptor's lock (Python < 3.12), not its locked state.
+    state = obj.__dict__.copy()
+    state.pop("func")
+    if sys.version_info < (3, 12):
+        state.pop("lock", None)
+    return functools.cached_property, (obj.func,), state
+
+
 def _weakset_reduce(obj):
     return weakref.WeakSet, (list(obj),)
 
@@ -1244,6 +1254,7 @@ class Pickler(pickle.Pickler):
     _dispatch_table[logging.RootLogger] = _root_logger_reduce
     _dispatch_table[memoryview] = _memoryview_reduce
     _dispatch_table[property] = _property_reduce
+    _dispatch_table[functools.cached_property] = _cached_property_reduce
     _dispatch_table[staticmethod] = _classmethod_reduce
     _dispatch_table[CellType] = _cell_reduce
     _dispatch_table[types.CodeType] = _code_reduce

tests/cloudpickle_test.py

@@ -1640,6 +1640,92 @@ def read_write_value(self, value):
         assert depickled_obj.read_write_value == 3
         type(depickled_obj).read_only_value.__doc__ == "A read-only attribute"
 
+    def test_cached_property(self):
+        class MyObject:
+            def __init__(self, value):
+                self.value = value
+                self.calls = 0
+
+            @functools.cached_property
+            def doubled(self):
+                "A cached result"
+                self.calls += 1
+                return self.value * 2
+
+        original = MyObject(3)
+        clone = subprocess_pickle_echo(original, protocol=self.protocol)
+        assert clone.doubled == 6
+        clone.value = 10
+        assert clone.doubled == 6
+        assert clone.calls == 1
+        del clone.doubled
+        assert clone.doubled == 20
+        assert clone.calls == 2
+        assert type(clone).doubled.__doc__ == "A cached result"
+
+        original.doubled
+        original.value = 10
+        clone = subprocess_pickle_echo(original, protocol=self.protocol)
+        assert clone.doubled == 6
+        assert clone.calls == 1
+
+    def test_cached_property_descriptor(self):
+        def func(obj):
+            "Original documentation"
+            return obj.value * 2
+
+        descriptor = functools.cached_property(func)
+        descriptor.__set_name__(object, "doubled")
+        descriptor.__doc__ = "Updated documentation"
+        descriptor.extra = [1, 2]
+        if sys.version_info >= (3, 12):
+            descriptor.lock = "a user-defined attribute"
+        clone, repeated = subprocess_pickle_echo(
+            [descriptor, descriptor], protocol=self.protocol
+        )
+        assert clone is repeated
+        assert clone.attrname == "doubled"
+        assert clone.__doc__ == "Updated documentation"
+        assert clone.extra == [1, 2]
+        if sys.version_info < (3, 12):
+            assert clone.lock is not descriptor.lock
+        else:
+            assert clone.lock == "a user-defined attribute"
+        obj = types.SimpleNamespace(value=4)
+        assert clone.__get__(obj) == 8
+        obj.value = 10
+        assert clone.__get__(obj) == 8
+
+    def test_cached_property_unbound(self):
+        descriptor = functools.cached_property(lambda obj: 42)
+        clone = subprocess_pickle_echo(descriptor, protocol=self.protocol)
+        assert clone.attrname is None
+        with pytest.raises(TypeError, match="__set_name__"):
+            clone.__get__(types.SimpleNamespace())
+        clone.__set_name__(object, "answer")
+        assert clone.__get__(types.SimpleNamespace()) == 42
+
+    def test_cached_property_class_in_fresh_process(self):
+        script = """
+            import functools
+            import cloudpickle
+            import pickle
+            import subprocess
+            import sys
+
+            class MyObject:
+                @functools.cached_property
+                def myself(self):
+                    return MyObject
+
+            payload = cloudpickle.dumps(MyObject, protocol={protocol})
+            code = "import pickle,sys; C=pickle.loads(sys.stdin.buffer.read()); "
+            code += "obj=C(); assert obj.myself is C; "
+            code += "assert obj.__dict__['myself'] is C"
+            subprocess.run([sys.executable, "-c", code], input=payload, check=True)
+        """
+        assert_run_python_script(textwrap.dedent(script.format(protocol=self.protocol)))
+
     def test_namedtuple(self):
         MyTuple = collections.namedtuple("MyTuple", ["a", "b", "c"])
         t1 = MyTuple(1, 2, 3)