Optimize attribute setting (#1741)

* Optimize attribute setting

* Add release note

---------

Co-authored-by: Davis Bennett <davis.v.bennett@gmail.com>

docs/release.rst

@@ -20,6 +20,9 @@ Unreleased
 
 Enhancements
 ~~~~~~~~~~~~
+* [v3] Dramatically reduce number of ``__contains_`` requests in favor of optimistically calling `__getitem__`
+  and handling any error that may arise.
+  By :user:`Deepak Cherian <dcherian>`.
 
 * [v3] Reuse the download array metadata when creating an ``Array``.
   By :user:`Deepak Cherian <dcherian>`.

zarr/attrs.py

@@ -151,19 +151,20 @@ def _put_nosync(self, d):
             if self.cache:
                 self._cached_asdict = d
         else:
-            if self.key in self.store:
+            try:
+                meta_unparsed = self.store[self.key]
                 # Cannot write the attributes directly to JSON, but have to
                 # store it within the pre-existing attributes key of the v3
                 # metadata.
 
                 # Note: this changes the store.counter result in test_caching_on!
 
-                meta = self.store._metadata_class.parse_metadata(self.store[self.key])
+                meta = self.store._metadata_class.parse_metadata(meta_unparsed)
                 if "attributes" in meta and "filters" in meta["attributes"]:
                     # need to preserve any existing "filters" attribute
                     d["attributes"]["filters"] = meta["attributes"]["filters"]
                 meta["attributes"] = d["attributes"]
-            else:
+            except KeyError:
                 meta = d
             self.store[self.key] = json_dumps(meta)
             if self.cache: