Add case for nan in categorical.__contains__

Author: fjetter

pandas/core/arrays/categorical.py

@@ -1851,6 +1851,8 @@ def __contains__(self, key):
         """Returns True if `key` is in this Categorical."""
         if key in self.categories:
             return self.categories.get_loc(key) in self.codes
+        elif isna(key) and self.isna().any():
+            return True
         else:
             return False
 

pandas/tests/indexes/test_category.py

@@ -244,6 +244,10 @@ def test_contains(self):
             list('aabbca') + [np.nan], categories=list('cabdef'))
         assert np.nan in ci
 
+        ci = CategoricalIndex(
+            list('aaa'), categories=list('cabdef'))
+        assert 'f' not in ci
+
     def test_min_max(self):
 
         ci = self.create_index(ordered=False)