fix: restore attrs del functionality

Author: ianhi

src/zarr/core/attributes.py

@@ -28,7 +28,7 @@ def __setitem__(self, key: str, value: JSON) -> None:
     def __delitem__(self, key: str) -> None:
         new_attrs = dict(self._obj.metadata.attributes)
         del new_attrs[key]
-        self._obj = self._obj.update_attributes(new_attrs)
+        self.put(new_attrs)
 
     def __iter__(self) -> Iterator[str]:
         return iter(self._obj.metadata.attributes)

tests/test_attributes.py

@@ -59,3 +59,12 @@ def test_update_no_changes() -> None:
 
     z.update_attributes({})
     assert dict(z.attrs) == {"a": [], "b": 3}
+
+
+def test_del_works() -> None:
+    store = zarr.storage.MemoryStore()
+    z = zarr.create(10, store=store, overwrite=True)
+    assert dict(z.attrs) == {}
+    z.update_attributes({"a": [3, 4], "c": 4})
+    del z.attrs["a"]
+    assert "c" in z.attrs