Fix bug with netcdf when units attribute is not a string (#7085)

* solve a bug when the units attribute is not a string (it happens that it is np.nan)

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* update the bug fixes section

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Anderson Banihirwe <[email protected]>
Co-authored-by: Tom Nicholas <[email protected]>

Author: 4 people

doc/whats-new.rst

@@ -42,6 +42,8 @@ Deprecations
 Bug fixes
 ~~~~~~~~~
 
+- Allow reading netcdf files where the 'units' attribute is a number(:pull:`7085`)
+  By `Ghislain Picard <https://github.com/ghislainp>`_.
 - Allow decoding of 0 sized datetimes(:issue:`1329`, :pull:`6882`)
   By `Deepak Cherian <https://github.com/dcherian>`_.
 - Make sure DataArray.name is always a string when used as label for plotting.

xarray/coding/times.py

@@ -681,7 +681,8 @@ def encode(self, variable, name=None):
     def decode(self, variable, name=None):
         dims, data, attrs, encoding = unpack_for_decoding(variable)
 
-        if "units" in attrs and "since" in attrs["units"]:
+        units = attrs.get("units")
+        if isinstance(units, str) and "since" in units:
             units = pop_to(attrs, encoding, "units")
             calendar = pop_to(attrs, encoding, "calendar")
             dtype = _decode_cf_datetime_dtype(data, units, calendar, self.use_cftime)

xarray/conventions.py

@@ -407,7 +407,8 @@ def _update_bounds_attributes(variables):
     # For all time variables with bounds
     for v in variables.values():
         attrs = v.attrs
-        has_date_units = "units" in attrs and "since" in attrs["units"]
+        units = attrs.get("units")
+        has_date_units = isinstance(units, str) and "since" in units
         if has_date_units and "bounds" in attrs:
             if attrs["bounds"] in variables:
                 bounds_attrs = variables[attrs["bounds"]].attrs

xarray/tests/test_coding_times.py

@@ -1167,3 +1167,11 @@ def test_decode_0size_datetime(use_cftime):
         use_cftime=use_cftime,
     )
     np.testing.assert_equal(expected, actual)
+
+
+@requires_cftime
+def test_scalar_unit() -> None:
+    # test that a scalar units (often NaN when using to_netcdf) does not raise an error
+    variable = Variable(("x", "y"), np.array([[0, 1], [2, 3]]), {"units": np.nan})
+    result = coding.times.CFDatetimeCoder().decode(variable)
+    assert np.isnan(result.attrs["units"])

xarray/tests/test_conventions.py

@@ -467,3 +467,11 @@ def test_decode_cf_variable_cftime():
     decoded = conventions.decode_cf_variable("time", variable)
     assert decoded.encoding == {}
     assert_identical(decoded, variable)
+
+
+def test_scalar_units() -> None:
+    # test that scalar units does not raise an exception
+    var = Variable(["t"], [np.nan, np.nan, 2], {"units": np.nan})
+
+    actual = conventions.decode_cf_variable("t", var)
+    assert_identical(actual, var)