Add ZARR_V3_API_AVAILABLE environment variable (#1007)

* add ZARR_V3_API_AVAILABLE environment variable

controls whether or not v3 stores are imported into the top-level zarr namespace

* move StoreV3 implementations from storage.py to storage_v3.py

* fix

* move zarr/storage_v3.py to zarr/_storage/v3.py

* Run Linux tests with ZARR_V3_API_AVAILABLE=1 defined

* add # pragma nocover to environment-variable dependent branches

* flake8 fix

* fix outdated import path

* fix mypy error

Author: grlee77

.github/workflows/python-package.yml

@@ -69,6 +69,7 @@ jobs:
         ZARR_TEST_ABS: 1
         ZARR_TEST_MONGO: 1
         ZARR_TEST_REDIS: 1
+        ZARR_V3_API_AVAILABLE: 1
       run: |
         conda activate zarr-env
         mkdir ~/blob_emulator

zarr/__init__.py

@@ -10,6 +10,7 @@
 from zarr.errors import CopyError, MetadataError
 from zarr.hierarchy import Group, group, open_group
 from zarr.n5 import N5Store, N5FSStore
+from zarr._storage.store import v3_api_available
 from zarr.storage import (ABSStore, DBMStore, DictStore, DirectoryStore,
                           KVStore, LMDBStore, LRUStoreCache, MemoryStore, MongoDBStore,
                           NestedDirectoryStore, RedisStore, SQLiteStore,
@@ -19,3 +20,8 @@
 
 # in case setuptools scm screw up and find version to be 0.0.0
 assert not __version__.startswith("0.0.0")
+
+if v3_api_available:
+    from zarr._storage.v3 import (ABSStoreV3, DBMStoreV3, KVStoreV3, DirectoryStoreV3,
+                                  LMDBStoreV3, LRUStoreCacheV3, MemoryStoreV3, MongoDBStoreV3,
+                                  RedisStoreV3, SQLiteStoreV3, ZipStoreV3)

zarr/_storage/store.py

@@ -1,4 +1,5 @@
 import abc
+import os
 from collections.abc import MutableMapping
 from string import ascii_letters, digits
 from typing import Any, List, Mapping, Optional, Union
@@ -17,6 +18,8 @@
 
 DEFAULT_ZARR_VERSION = 2
 
+v3_api_available = os.environ.get('ZARR_V3_API_AVAILABLE', '0').lower() not in ['0', 'false']
+
 
 class BaseStore(MutableMapping):
     """Abstract base class for store implementations.
@@ -261,7 +264,7 @@ def _ensure_store(store):
 
         We'll do this conversion in a few places automatically
         """
-        from zarr.storage import KVStoreV3  # avoid circular import
+        from zarr._storage.v3 import KVStoreV3  # avoid circular import
         if store is None:
             return None
         elif isinstance(store, StoreV3):