changed according to comments

pandas/core/arrays/categorical.py

@@ -184,9 +184,11 @@ def contains(cat, key, container):
 
     Notes
     -----
-    This method does not check for Nan values. Do that separately
+    This method does not check for NaN values. Do that separately
     before calling this method.
     """
+    hash(key)
+
     # get location of key in categories.
     # If a KeyError, the key isn't in categories, so logically
     #  can't be in container either.
@@ -1898,9 +1900,8 @@ def __iter__(self):
 
     def __contains__(self, key):
         """Returns True if `key` is in this Categorical."""
-        hash(key)
-
-        if isna(key):  # if key is a NaN, check if any NaN is in self.
+        # if key is a NaN, check if any NaN is in self.
+        if isna(key):
             return self.isna().any()
 
         return contains(self, key, container=self._codes)

pandas/core/indexes/category.py

@@ -322,16 +322,14 @@ def _reverse_indexer(self):
 
     @Appender(_index_shared_docs['__contains__'] % _index_doc_kwargs)
     def __contains__(self, key):
-        hash(key)
-
-        if isna(key):  # if key is a NaN, check if any NaN is in self.
+        # if key is a NaN, check if any NaN is in self.
+        if isna(key):
             return self.hasnans
 
         return contains(self, key, container=self._engine)
 
     @Appender(_index_shared_docs['contains'] % _index_doc_kwargs)
     def contains(self, key):
-        hash(key)
         return key in self
 
     def __array__(self, dtype=None):

pandas/tests/categorical/test_algos.py

@@ -71,22 +71,6 @@ def test_isin_empty(empty):
     tm.assert_numpy_array_equal(expected, result)
 
 
-def test_contains():
-    # GH21508
-    c = pd.Categorical(list('aabbca'), categories=list('cab'))
-
-    assert 'b' in c
-    assert 'z' not in c
-    assert np.nan not in c
-
-    # assert codes NOT in index
-    assert 0 not in c
-    assert 1 not in c
-
-    c = pd.Categorical(list('aabbca') + [np.nan], categories=list('cab'))
-    assert np.nan in c
-
-
 class TestTake(object):
     # https://github.com/pandas-dev/pandas/issues/20664
 

pandas/tests/categorical/test_operators.py

@@ -291,3 +291,20 @@ def test_numeric_like_ops(self):
 
         # invalid ufunc
         pytest.raises(TypeError, lambda: np.log(s))
+
+    def test_contains(self):
+        # GH21508
+        c = pd.Categorical(list('aabbca'), categories=list('cab'))
+
+        assert 'b' in c
+        assert 'z' not in c
+        assert np.nan not in c
+        with pytest.raises(TypeError):
+            assert [1] in c
+
+        # assert codes NOT in index
+        assert 0 not in c
+        assert 1 not in c
+
+        c = pd.Categorical(list('aabbca') + [np.nan], categories=list('cab'))
+        assert np.nan in c