document default compressor

Author: alimanfoo

docs/tutorial.rst

@@ -220,12 +220,12 @@ compression, level 1::
       store: dict
 
 Here is an example using LZMA with a custom filter pipeline including
-the delta filter::
+LZMA's built-in delta filter::
 
     >>> import lzma
-    >>> filters = [dict(id=lzma.FILTER_DELTA, dist=4),
-    ...            dict(id=lzma.FILTER_LZMA2, preset=1)]
-    >>> compressor = zarr.LZMA(filters=filters)
+    >>> lzma_filters = [dict(id=lzma.FILTER_DELTA, dist=4),
+    ...                 dict(id=lzma.FILTER_LZMA2, preset=1)]
+    >>> compressor = zarr.LZMA(filters=lzma_filters)
     >>> z = zarr.array(np.arange(100000000, dtype='i4').reshape(10000, 10000),
     ...                chunks=(1000, 1000), compressor=compressor)
     >>> z
@@ -234,7 +234,28 @@ the delta filter::
       compressor: LZMA(format=1, check=-1, preset=None, filters=[{'dist': 4, 'id': 3}, {'preset': 1, 'id': 33}])
       store: dict
 
-To disable compression, set ``compressor=None`` when creating an array.
+The default compressor can be changed by setting the value of the
+``zarr.storage.default_compressor`` variable, e.g.::
+
+    >>> import zarr.storage
+    >>> # switch to using Zstandard via Blosc by default
+    ... zarr.storage.default_compressor = zarr.Blosc(cname='zstd', clevel=1, shuffle=1)
+    >>> z = zarr.zeros(100000000, chunks=1000000)
+    >>> z
+    Array((100000000,), float64, chunks=(1000000,), order=C)
+      nbytes: 762.9M; nbytes_stored: 302; ratio: 2649006.6; initialized: 0/100
+      compressor: Blosc(cname='zstd', clevel=1, shuffle=1)
+      store: dict
+    >>> # switch back to Blosc defaults
+    ... zarr.storage.default_compressor = zarr.Blosc()
+
+To disable compression, set ``compressor=None`` when creating an array, e.g.::
+
+    >>> z = zarr.zeros(100000000, chunks=1000000, compressor=None)
+    >>> z
+    Array((100000000,), float64, chunks=(1000000,), order=C)
+      nbytes: 762.9M; nbytes_stored: 209; ratio: 3827751.2; initialized: 0/100
+      store: dict
 
 .. _tutorial_filters:
 

zarr/tests/test_core.py

@@ -512,6 +512,7 @@ def test_np_ufuncs(self):
         zi = self.create_array(shape=indices.shape, dtype=indices.dtype,
                                chunks=10, filters=None)
         zi[:] = indices
+        # this triggers __array__() call with dtype argument
         assert_array_equal(np.take(a, indices, axis=1),
                            np.take(a, zi, axis=1))
 

zarr/tests/test_hierarchy.py

@@ -488,7 +488,7 @@ def test_getattr(self):
         # setup
         g1 = self.create_group()
         g2 = g1.create_group('foo')
-        d1 = g2.create_dataset('bar', shape=100)
+        g2.create_dataset('bar', shape=100)
 
         # test
         eq(g1['foo'], g1.foo)