Fix unpickling by defining __setstate__ (#302)

Author: dcherian

cf_xarray/accessor.py

@@ -933,6 +933,9 @@ def __init__(self, obj):
         self._obj = obj
         self._all_cell_measures = None
 
+    def __setstate__(self, d):
+        self.__dict__ = d
+
     def _assert_valid_other_comparison(self, other):
         flag_dict = create_flag_dict(self._obj)
         if other not in flag_dict:

cf_xarray/tests/test_accessor.py

@@ -1,4 +1,5 @@
 import itertools
+import pickle
 from textwrap import dedent
 from urllib.request import urlopen
 
@@ -1545,3 +1546,10 @@ def test_missing_variables():
     ds = vert.copy(deep=True)
     ds = ds.drop_vars("ap")
     assert ds.cf.formula_terms == {"lev": {"b": "b", "ps": "ps"}}
+
+
+def test_pickle():
+    da = xr.DataArray([1.0], name="a")
+    ds = da.to_dataset()
+    pickle.loads(pickle.dumps(da.cf))
+    pickle.loads(pickle.dumps(ds.cf))