check type of attribute keys (#1066)

* check type of attribute keys

* introduce deprecation cycle

* fix typo

* stringify keys

* cleanup

* do not cover except

zarr/attrs.py

@@ -1,3 +1,4 @@
+import warnings
 from collections.abc import MutableMapping
 
 from zarr._storage.store import Store, StoreV3
@@ -128,6 +129,27 @@ def put(self, d):
             self._write_op(self._put_nosync, dict(attributes=d))
 
     def _put_nosync(self, d):
+
+        d_to_check = d if self._version == 2 else d["attributes"]
+        if not all(isinstance(item, str) for item in d_to_check):
+            # TODO: Raise an error for non-string keys
+            # raise TypeError("attribute keys must be strings")
+            warnings.warn(
+                "only attribute keys of type 'string' will be allowed in the future",
+                DeprecationWarning,
+                stacklevel=2
+                )
+
+            try:
+                d_to_check = {str(k): v for k, v in d_to_check.items()}
+            except TypeError as ex:  # pragma: no cover
+                raise TypeError("attribute keys can not be stringified") from ex
+
+            if self._version == 2:
+                d = d_to_check
+            else:
+                d["attributes"] = d_to_check
+
         if self._version == 2:
             self.store[self.key] = json_dumps(d)
             if self.cache:

zarr/tests/test_attrs.py

@@ -268,3 +268,18 @@ def test_caching_off(self, zarr_version):
         get_cnt = 10 if zarr_version == 2 else 12
         assert get_cnt == store.counter['__getitem__', attrs_key]
         assert 3 == store.counter['__setitem__', attrs_key]
+
+    def test_wrong_keys(self, zarr_version):
+        store = _init_store(zarr_version)
+        a = self.init_attributes(store, zarr_version=zarr_version)
+
+        warning_msg = "only attribute keys of type 'string' will be allowed in the future"
+
+        with pytest.warns(DeprecationWarning, match=warning_msg):
+            a[1] = "foo"
+
+        with pytest.warns(DeprecationWarning, match=warning_msg):
+            a.put({1: "foo"})
+
+        with pytest.warns(DeprecationWarning, match=warning_msg):
+            a.update({1: "foo"})