Take flattened array views to avoid some copies

Make use of Numcodecs' `ensure_contiguous_ndarray` to take `ndarray`
views onto buffers to be stored in a few cases so as to reshape them and
avoid a copy (thanks to the buffer protocol). This ensures that
datetime/timedeltas are handled by default. Also catches things like
object arrays. Finally this handles flattening the array if needed.
All-in-all this gets as close to a `bytes` object as possible while not
copying and doing its best to preserve type information while
constructing something that fits the buffer protocol.

Author: jakirkham

zarr/storage.py

@@ -31,16 +31,13 @@
 import warnings
 
 
-import numpy as np
-
-
 from zarr.util import (normalize_shape, normalize_chunks, normalize_order,
                        normalize_storage_path, buffer_size,
                        normalize_fill_value, nolock, normalize_dtype)
 from zarr.meta import encode_array_metadata, encode_group_metadata
 from zarr.compat import PY2, OrderedDict_move_to_end
 from numcodecs.registry import codec_registry
-from numcodecs.compat import ensure_bytes
+from numcodecs.compat import ensure_bytes, ensure_contiguous_ndarray
 from zarr.errors import (err_contains_group, err_contains_array, err_bad_compressor,
                          err_fspath_exists_notdir, err_read_only, MetadataError)
 
@@ -725,9 +722,8 @@ def __getitem__(self, key):
 
     def __setitem__(self, key, value):
 
-        # handle F-contiguous numpy arrays
-        if isinstance(value, np.ndarray) and value.flags.f_contiguous:
-            value = ensure_bytes(value)
+        # coerce to flat, contiguous array (ideally without copying)
+        value = ensure_contiguous_ndarray(value)
 
         # destination path for key
         file_path = os.path.join(self.path, key)
@@ -1176,7 +1172,7 @@ def __getitem__(self, key):
     def __setitem__(self, key, value):
         if self.mode == 'r':
             err_read_only()
-        value = ensure_bytes(value)
+        value = ensure_contiguous_ndarray(value)
         with self.mutex:
             self.zf.writestr(key, value)