support property pickling in python 3.8 + (#329)

Author: pierreglaser

Diff for: CHANGES.md

@@ -1,6 +1,10 @@
 1.2.3
 =====
 
+- Fix a regression in cloudpickle and python3.8 causing an error when trying to
+  pickle property objects.
+  ([PR #329](https://github.com/cloudpipe/cloudpickle/pull/329)).
+
 - Fix a bug when a thread imports a module while cloudpickle iterates
   over the module list
   ([PR #322](https://github.com/cloudpipe/cloudpickle/pull/322)).

Diff for: cloudpickle/cloudpickle_fast.py

@@ -291,6 +291,10 @@ def _root_logger_reduce(obj):
     return logging.getLogger, ()
 
 
+def _property_reduce(obj):
+    return property, (obj.fget, obj.fset, obj.fdel, obj.__doc__)
+
+
 def _weakset_reduce(obj):
     return weakref.WeakSet, (list(obj),)
 
@@ -406,6 +410,7 @@ class CloudPickler(Pickler):
     dispatch[logging.Logger] = _logger_reduce
     dispatch[logging.RootLogger] = _root_logger_reduce
     dispatch[memoryview] = _memoryview_reduce
+    dispatch[property] = _property_reduce
     dispatch[staticmethod] = _classmethod_reduce
     dispatch[types.CellType] = _cell_reduce
     dispatch[types.CodeType] = _code_reduce

Diff for: tests/cloudpickle_test.py

@@ -1119,6 +1119,50 @@ def func(x):
         cloned = pickle_depickle(func, protocol=self.protocol)
         self.assertEqual(cloned.__qualname__, func.__qualname__)
 
+    def test_property(self):
+        class MyObject:
+            _read_only_value = 1
+            _read_write_value = 1
+
+            @property
+            def read_only_value(self):
+                "A read-only attribute"
+                return self._read_only_value
+
+            @property
+            def read_write_value(self):
+                return self._read_write_value
+
+            @read_write_value.setter
+            def read_write_value(self, value):
+                self._read_write_value = value
+
+
+
+        my_object = MyObject()
+
+        assert my_object.read_only_value == 1
+        assert MyObject.read_only_value.__doc__ == "A read-only attribute"
+
+        with pytest.raises(AttributeError):
+            my_object.read_only_value = 2
+        my_object.read_write_value = 2
+
+        depickled_obj = pickle_depickle(my_object)
+
+        assert depickled_obj.read_only_value == 1
+        assert depickled_obj.read_write_value == 2
+
+        # make sure the depickled read_only_value attribute is still read-only
+        with pytest.raises(AttributeError):
+            my_object.read_only_value = 2
+
+        # make sure the depickled read_write_value attribute is writeable
+        depickled_obj.read_write_value = 3
+        assert depickled_obj.read_write_value == 3
+        type(depickled_obj).read_only_value.__doc__ == "A read-only attribute"
+
+
     def test_namedtuple(self):
         MyTuple = collections.namedtuple('MyTuple', ['a', 'b', 'c'])
         t1 = MyTuple(1, 2, 3)