Merge pull request #529 from petercable/f64

Issue #526 F8 values are incorrectly coerced to F4 when writing NETCD…

Author: shoyer

doc/whats-new.rst

@@ -9,6 +9,15 @@ What's New
     import xray
     np.random.seed(123456)
 
+v0.6.0 (unreleased)
+-------------------
+
+Bug fixes
+~~~~~~~~~
+
+- Fixed unnecessary coercion of float64 to float32 when using netcdf3 and
+  netcdf4_classic formats (:issue:`526`).
+
 v0.5.3 (unreleased)
 -------------------
 

xray/backends/netcdf3.py

@@ -19,8 +19,7 @@
 
 # These data-types aren't supported by netCDF3, so they are automatically
 # coerced instead as indicated by the "coerce_nc3_dtype" function
-_nc3_dtype_coercions = {'int64': 'int32', 'float64': 'float32',
-                        'bool': 'int8'}
+_nc3_dtype_coercions = {'int64': 'int32', 'bool': 'int8'}
 
 
 def coerce_nc3_dtype(arr):

xray/test/test_backends.py

@@ -196,6 +196,11 @@ def test_roundtrip_timedelta_data(self):
         with self.roundtrip(expected) as actual:
             self.assertDatasetIdentical(expected, actual)
 
+    def test_roundtrip_float64_data(self):
+        expected = Dataset({'x': ('y', np.array([1.0, 2.0, np.pi], dtype='float64'))})
+        with self.roundtrip(expected) as actual:
+            self.assertDatasetIdentical(expected, actual)
+
     def test_roundtrip_example_1_netcdf(self):
         expected = open_example_dataset('example_1.nc')
         with self.roundtrip(expected) as actual:
@@ -266,7 +271,7 @@ def test_roundtrip_strings_with_fill_value(self):
             # netCDF4 can't keep track of an empty _FillValue for VLEN
             # variables
             expected['x'][-1] = ''
-        elif (type(self) is NetCDF3ViaNetCDF4DataTest
+        elif (isinstance(self, (NetCDF3ViaNetCDF4DataTest, NetCDF4ClassicViaNetCDF4DataTest))
               or (has_netCDF4 and type(self) is GenericNetCDFDataTest)):
             # netCDF4 can't keep track of an empty _FillValue for nc3, either:
             # https://github.com/Unidata/netcdf4-python/issues/273
@@ -651,6 +656,24 @@ def roundtrip(self, data, **kwargs):
                 yield ds
 
 
+@requires_netCDF4
+class NetCDF4ClassicViaNetCDF4DataTest(CFEncodedDataTest, Only32BitTypes, TestCase):
+    @contextlib.contextmanager
+    def create_store(self):
+        with create_tmp_file() as tmp_file:
+            with backends.NetCDF4DataStore(tmp_file, mode='w',
+                                           format='NETCDF4_CLASSIC') as store:
+                yield store
+
+    @contextlib.contextmanager
+    def roundtrip(self, data, **kwargs):
+        with create_tmp_file() as tmp_file:
+            data.to_netcdf(tmp_file, format='NETCDF4_CLASSIC',
+                           engine='netcdf4')
+            with open_dataset(tmp_file, engine='netcdf4', **kwargs) as ds:
+                yield ds
+
+
 @requires_scipy_or_netCDF4
 class GenericNetCDFDataTest(CFEncodedDataTest, Only32BitTypes, TestCase):
     # verify that we can read and write netCDF3 files as long as we have scipy