Make Patch pickleable

CHANGELOG.md

@@ -6,6 +6,7 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 
 ## Fixed
 
+- [#2498](https://github.com/plotly/dash/pull/2498) Fix error when caching callbacks which return `Patch` objects by making `Patch` objects picklable
 - [#2491](https://github.com/plotly/dash/pull/2491) Fix clientside inline function name not found, fix [#2488](https://github.com/plotly/dash/issues/2488)
 
 ## [2.9.2] - 2023-03-29

dash/_patch.py

@@ -30,6 +30,12 @@ def __init__(self, location=None, parent=None):
         else:
             self._operations = []
 
+    def __getstate__(self):
+        return vars(self)
+
+    def __setstate__(self, state):
+        vars(self).update(state)
+
     def __getitem__(self, item):
         validate_slice(item)
         return Patch(location=self._location + [item], parent=self)

tests/unit/test_patch.py

@@ -244,3 +244,14 @@ def test_pat019_patch_remove():
         "location": [],
         "params": {"value": "item"},
     }
+
+
+def test_pat020_patch_pickle():
+    import pickle
+
+    p = Patch()
+    p["a"] = "a"
+    data = pickle.dumps(p)
+    q = pickle.loads(data)
+
+    assert patch_to_dict(p) == patch_to_dict(q)