CF: also decode time bounds when available

doc/whats-new.rst

@@ -36,6 +36,10 @@ Breaking changes
 Enhancements
 ~~~~~~~~~~~~
 
+- Time bounds variables are now also decoded according to CF conventions
+  (:issue:`2565`).
+  By `Fabien Maussion <https://github.com/fmaussion>`_.
+
 Bug fixes
 ~~~~~~~~~
 

xarray/conventions.py

@@ -350,6 +350,25 @@ def stackable(dim):
         drop_variables = []
     drop_variables = set(drop_variables)
 
+    # Time bounds coordinates might miss the decoding attributes
+    # https://github.com/pydata/xarray/issues/2565
+    if decode_times:
+        # We list all time variables with bounds
+        to_update = dict()
+        for v in variables.values():
+            attrs = v.attrs
+            if ('units' in attrs and 'since' in attrs['units'] and
+                    'bounds' in attrs):
+                new_attrs = {'units': attrs['units']}
+                if 'calendar' in attrs:
+                    new_attrs['calendar'] = attrs['calendar']
+                to_update[attrs['bounds']] = new_attrs
+        # For all bound variables, update their time attribute if not present
+        for k, new_attrs in to_update.items():
+            if k in variables:
+                for ak, av in new_attrs.items():
+                    variables[k].attrs.setdefault(ak, av)
+
     new_vars = OrderedDict()
     for k, v in iteritems(variables):
         if k in drop_variables:

xarray/tests/test_coding_times.py

@@ -624,6 +624,62 @@ def test_decode_cf(calendar):
             assert ds.test.dtype == np.dtype('M8[ns]')
 
 
+def test_decode_cf_time_bounds():
+
+    da = DataArray(np.arange(6).reshape((3, 2)), coords={'time': [1, 2, 3]},
+                   dims=('time', 'nbnd'), name='time_bnds')
+
+    # Simplest case
+    ds = da.to_dataset()
+    ds['time'].attrs['units'] = 'days since 2001-01-01'
+    ds['time'].attrs['calendar'] = 'standard'
+    ds['time'].attrs['bounds'] = 'time_bnds'
+    ds = decode_cf(ds)
+    assert ds.time_bnds.dtype == np.dtype('M8[ns]')
+
+    # Without calendar also OK
+    ds = da.to_dataset()
+    ds['time'].attrs['units'] = 'days since 2001-01-01'
+    ds['time'].attrs['bounds'] = 'time_bnds'
+    ds = decode_cf(ds)
+    assert ds.time_bnds.dtype == np.dtype('M8[ns]')
+
+    # If previous calendar and units do not overwrite them
+    if has_cftime_or_netCDF4:
+        ds = da.to_dataset()
+        ds['time'].attrs['units'] = 'days since 2001-01-01'
+        ds['time'].attrs['calendar'] = 'standard'
+        ds['time'].attrs['bounds'] = 'time_bnds'
+        ds['time_bnds'].attrs['units'] = 'hours since 2001-01-01'
+        ds['time_bnds'].attrs['calendar'] = 'noleap'
+        ds = decode_cf(ds)
+        assert ds.time_bnds.dtype == np.dtype('O')
+        assert ds.time_bnds.encoding['units'] == 'hours since 2001-01-01'
+
+    # If bounds not available do not complain
+    ds = da.to_dataset()
+    ds['time'].attrs['units'] = 'days since 2001-01-01'
+    ds['time'].attrs['calendar'] = 'standard'
+    ds['time'].attrs['bounds'] = 'fake_time_bnds'
+    ds = decode_cf(ds)
+    assert ds.time_bnds.dtype == np.dtype('int64')
+
+    # If not proper time do not change bounds
+    ds = da.to_dataset()
+    ds['time'].attrs['units'] = 'days in 2001-01-01'
+    ds['time'].attrs['calendar'] = 'standard'
+    ds['time'].attrs['bounds'] = 'time_bnds'
+    ds = decode_cf(ds)
+    assert ds.time_bnds.dtype == np.dtype('int64')
+
+    # Only decode if asked for
+    ds = da.to_dataset()
+    ds['time'].attrs['units'] = 'days since 2001-01-01'
+    ds['time'].attrs['bounds'] = 'time_bnds'
+    ds = decode_cf(ds, decode_times=False)
+    assert ds.time_bnds.dtype == np.dtype('int64')
+
+
 @pytest.fixture(params=_ALL_CALENDARS)
 def calendar(request):
     return request.param