Make partial decompress opt-in, extend whatsnew.

Author: Carreau

docs/release.rst

@@ -31,14 +31,16 @@ See `this link <https://github.com/zarr-developers/zarr-python/milestone/11?clos
 merged PR tagged with the 2.6 milestone.
 
 * Add ability to partially read and decompress arrays, see :issue:`667`. IT is
-  only available to chunks fored via fs-spec and using bloc as a compressor. 
+  only available to chunks stored using fs-spec and using bloc as a compressor.
 
   For certain analysis case when only a small portion of chunks is needed it can
   be advantageous to only access and decompress part of the chunks. Doing
   partial read and decompression add high latency to many of the operation so
   should be used only when the subset of the data is small compared to the full
-  chunks and is stored contiguously (last dimensions for C layout, firsts for
-  F). Set ``partial_decompress=True`` when creating an ``Array``
+  chunks and is stored contiguously (that is to say either last dimensions for C
+  layout, firsts for F). Pass ``partial_decompress=True`` as argument when
+  creating an ``Array``, or when using ``open_array``. No option exists yet to
+  apply partial read and decompress on a per-operation basis.
 
 2.5.0
 -----

zarr/core.py

@@ -71,10 +71,12 @@ class Array:
         operations. If False, user attributes are reloaded from the store prior
         to all attribute read operations.
     partial_decompress : bool, optional
-        If True and while the chunk_store is a FSStore and the compreesion used
+        If True and while the chunk_store is a FSStore and the compresion used
         is Blosc, when getting data from the array chunks will be partially
         read and decompressed when possible.
 
+        .. versionadded:: 2.7
+
     Attributes
     ----------
     store
@@ -134,7 +136,7 @@ def __init__(
         synchronizer=None,
         cache_metadata=True,
         cache_attrs=True,
-        partial_decompress=True,
+        partial_decompress=False,
     ):
         # N.B., expect at this point store is fully initialized with all
         # configuration metadata fully specified and normalized

zarr/creation.py

@@ -362,11 +362,26 @@ def array(data, **kwargs):
     return z
 
 
-def open_array(store=None, mode='a', shape=None, chunks=True, dtype=None,
-               compressor='default', fill_value=0, order='C', synchronizer=None,
-               filters=None, cache_metadata=True, cache_attrs=True, path=None,
-               object_codec=None, chunk_store=None, storage_options=None,
-               **kwargs):
+def open_array(
+    store=None,
+    mode="a",
+    shape=None,
+    chunks=True,
+    dtype=None,
+    compressor="default",
+    fill_value=0,
+    order="C",
+    synchronizer=None,
+    filters=None,
+    cache_metadata=True,
+    cache_attrs=True,
+    path=None,
+    object_codec=None,
+    chunk_store=None,
+    storage_options=None,
+    partial_decompress=False,
+    **kwargs
+):
     """Open an array using file-mode-like semantics.
 
     Parameters
@@ -415,6 +430,7 @@ def open_array(store=None, mode='a', shape=None, chunks=True, dtype=None,
     storage_options : dict
         If using an fsspec URL to create the store, these will be passed to
         the backend implementation. Ignored otherwise.
+    partial_decompress:
 
     Returns
     -------