Forward mode option through normalize store args.

Closes #269

Author: Carreau

docs/release.rst

@@ -10,6 +10,9 @@ This release will be the first release of Zarr not supporting Python 3.5.
 * End Python 3.5 support.
   By :user:`Chris Barnes <clbarnes>`; :issue:`602`.
 
+* Fix ``open_group/open_array`` to allow opening of readonly store with
+  ``mode='r'`` :issue:`269`
+
 * Add `Array` tests for FSStore.
   By :user:`Andrew Fulton <andrewfulton9>`; :issue: `644`.
 

zarr/creation.py

@@ -129,11 +129,11 @@ def create(shape, chunks=True, dtype=None, compressor='default',
     return z
 
 
-def normalize_store_arg(store, clobber=False, storage_options=None):
+def normalize_store_arg(store, clobber=False, storage_options=None, mode='w'):
     if store is None:
         return dict()
     elif isinstance(store, str):
-        mode = 'w' if clobber else 'r'
+        mode = mode if clobber else "r"
         if "://" in store or "::" in store:
             return FSStore(store, mode=mode, **(storage_options or {}))
         elif storage_options:
@@ -450,8 +450,8 @@ def open_array(store=None, mode='a', shape=None, chunks=True, dtype=None,
     # a : read/write if exists, create otherwise (default)
 
     # handle polymorphic store arg
-    clobber = mode == 'w'
-    store = normalize_store_arg(store, clobber=clobber, storage_options=storage_options)
+    clobber = (mode == 'w')
+    store = normalize_store_arg(store, clobber=clobber, storage_options=storage_options, mode=mode)
     if chunk_store is not None:
         chunk_store = normalize_store_arg(chunk_store, clobber=clobber,
                                           storage_options=storage_options)

zarr/hierarchy.py

@@ -1035,11 +1035,11 @@ def move(self, source, dest):
         self._write_op(self._move_nosync, source, dest)
 
 
-def _normalize_store_arg(store, clobber=False, storage_options=None):
+def _normalize_store_arg(store, *, clobber=False, storage_options=None, mode=None):
     if store is None:
         return MemoryStore()
     return normalize_store_arg(store, clobber=clobber,
-                               storage_options=storage_options)
+                               storage_options=storage_options, mode=mode)
 
 
 def group(store=None, overwrite=False, chunk_store=None,
@@ -1148,8 +1148,10 @@ def open_group(store=None, mode='a', cache_attrs=True, synchronizer=None, path=N
     """
 
     # handle polymorphic store arg
-    clobber = mode != 'r'
-    store = _normalize_store_arg(store, clobber=clobber, storage_options=storage_options)
+    clobber = mode != "r"
+    store = _normalize_store_arg(
+        store, clobber=clobber, storage_options=storage_options, mode=mode
+    )
     if chunk_store is not None:
         chunk_store = _normalize_store_arg(chunk_store, clobber=clobber,
                                            storage_options=storage_options)