Keep patched values independent of the diff

dictdiffer/__init__.py

@@ -294,6 +294,7 @@ def patch(diff_result, destination, in_place=False):
 
     def add(node, changes):
         for key, value in changes:
+            value = deepcopy(value)
             dest = dot_lookup(destination, node)
             if isinstance(dest, LIST_TYPES):
                 dest.insert(key, value)
@@ -311,7 +312,7 @@ def change(node, changes):
         if isinstance(dest, LIST_TYPES):
             last_node = int(last_node)
         _, value = changes
-        dest[last_node] = value
+        dest[last_node] = deepcopy(value)
 
     def remove(node, changes):
         for key, value in changes:

tests/test_dictdiffer.py

@@ -753,5 +753,18 @@ def test_ignore_dotted_ignore_key(ignore, dot_notation, diff_size):
                   ignore=[ignore])))
 
 
+@pytest.mark.parametrize('first', [{}, {'value': None}])
+@pytest.mark.parametrize('in_place', [False, True])
+def test_patch_does_not_alias_diff_values(first, in_place):
+    first = dict(first)
+    second = {'value': {'items': [1]}}
+    changes = list(diff(first, second))
+    original_changes = list(diff(first, second))
+    result = patch(changes, first, in_place=in_place)
+    result['value']['items'].append(2)
+    assert changes == original_changes
+    assert patch(changes, {})['value'] == {'items': [1]}
+
+
 if __name__ == "__main__":
     unittest.main()