finish up datetime support

Author: alimanfoo

docs/tutorial.rst

@@ -1079,10 +1079,10 @@ E.g., pickle/unpickle an array stored on disk::
 Datetimes and timedeltas
 ------------------------
 
-NumPy's ``datetime64`` ('M') and ``timedelta64`` ('m') dtypes are supported for Zarr
+NumPy's ``datetime64`` ('M8') and ``timedelta64`` ('m8') dtypes are supported for Zarr
 arrays, as long as the units are specified. E.g.::
 
-    >>> z = zarr.array(['2007-07-13', '2006-01-13', '2010-08-13'], dtype='M[D]')
+    >>> z = zarr.array(['2007-07-13', '2006-01-13', '2010-08-13'], dtype='M8[D]')
     >>> z
     <zarr.core.Array (3,) datetime64[D]>
     >>> z[:]

zarr/meta.py

@@ -178,5 +178,7 @@ def encode_fill_value(v, dtype):
         return v
     elif dtype.kind == 'U':
         return v
+    elif dtype.kind in 'mM':
+        return int(v.view('u8'))
     else:
         return v

zarr/tests/test_core.py

@@ -874,7 +874,7 @@ def test_dtypes(self):
         for base_type in 'Mm':
             for resolution in 'D', 'us', 'ns':
                 dtype = '{}8[{}]'.format(base_type, resolution)
-                z = self.create_array(shape=100, dtype=dtype)
+                z = self.create_array(shape=100, dtype=dtype, fill_value=0)
                 assert z.dtype == np.dtype(dtype)
                 a = np.random.randint(0, np.iinfo('u8').max, size=z.shape[0],
                                       dtype='u8').view(dtype)

zarr/util.py

@@ -145,7 +145,7 @@ def normalize_dtype(dtype, object_codec):
                     args = ()
                 try:
                     object_codec = codec_registry[codec_id](*args)
-                except KeyError:
+                except KeyError:  # pragma: no cover
                     raise ValueError('codec %r for object type %r is not '
                                      'available; please provide an '
                                      'object_codec manually' % (codec_id, key))