Array & Group: Use already loaded attributes to populate cache. (#1734)

* Array: Use already loaded attributes to populate cache.

* Group: Use already loaded attributes to populate cache.

* Fix

* Add release note

Author: dcherian

docs/release.rst

@@ -21,8 +21,12 @@ Unreleased
 Enhancements
 ~~~~~~~~~~~~
 
+* [v3] Reuse the download array metadata when creating an ``Array``.
+  By :user:`Deepak Cherian <dcherian>`.
+
 * Optimize ``Array.info`` so that it calls `getsize` only once.
   By :user:`Deepak Cherian <dcherian>`.
+
 * Override IPython ``_repr_*_`` methods to avoid expensive lookups against object stores.
   By :user:`Deepak Cherian <dcherian>` :issue:`1716`.
 

zarr/attrs.py

@@ -25,14 +25,16 @@ class Attributes(MutableMapping):
 
     """
 
-    def __init__(self, store, key=".zattrs", read_only=False, cache=True, synchronizer=None):
+    def __init__(
+        self, store, key=".zattrs", read_only=False, cache=True, synchronizer=None, cached_dict=None
+    ):
         self._version = getattr(store, "_store_version", 2)
         _Store = Store if self._version == 2 else StoreV3
         self.store = _Store._ensure_store(store)
         self.key = key
         self.read_only = read_only
         self.cache = cache
-        self._cached_asdict = None
+        self._cached_asdict = cached_dict if cache else None
         self.synchronizer = synchronizer
 
     def _get_nosync(self):

zarr/core.py

@@ -172,7 +172,12 @@ def __init__(
         # initialize attributes
         akey = _prefix_to_attrs_key(self._store, self._key_prefix)
         self._attrs = Attributes(
-            store, key=akey, read_only=read_only, synchronizer=synchronizer, cache=cache_attrs
+            store,
+            key=akey,
+            read_only=read_only,
+            synchronizer=synchronizer,
+            cache=cache_attrs,
+            cached_dict=self._meta["attributes"] if self._version == 3 else None,
         )
 
         # initialize info reporter

zarr/hierarchy.py

@@ -208,7 +208,12 @@ def __init__(
             # object can still be created.
             akey = mkey
         self._attrs = Attributes(
-            store, key=akey, read_only=read_only, cache=cache_attrs, synchronizer=synchronizer
+            store,
+            key=akey,
+            read_only=read_only,
+            cache=cache_attrs,
+            synchronizer=synchronizer,
+            cached_dict=self._meta["attributes"] if self._version == 3 and self._meta else None,
         )
 
         # setup info