disallow numeric setlike operations on CategoricalIndex (GH10039)

Author: jreback

pandas/core/index.py

@@ -2469,6 +2469,21 @@ def _evaluate_compare(self, other):
         cls.__le__ = _make_compare('__le__')
         cls.__ge__ = _make_compare('__ge__')
 
+    @classmethod
+    def _add_numericlike_set_methods_disabled(cls):
+        """ add in the numeric set-like methods to disable """
+
+        def _make_invalid_op(name):
+
+            def invalid_op(self, other=None):
+                raise TypeError("cannot perform {name} with this index type: {typ}".format(name=name,
+                                                                                           typ=type(self)))
+            invalid_op.__name__ = name
+            return invalid_op
+
+        cls.__add__ = cls.__add__ = __iadd__ = _make_invalid_op('__add__')
+        cls.__sub__ = cls.__sub__ = __isub__ = _make_invalid_op('__sub__')
+
     @classmethod
     def _add_numeric_methods_disabled(cls):
         """ add in numeric methods to disable """
@@ -3148,6 +3163,7 @@ def _add_accessors(cls):
                                                  overwrite=True)
 
 
+CategoricalIndex._add_numericlike_set_methods_disabled()
 CategoricalIndex._add_numeric_methods_disabled()
 CategoricalIndex._add_logical_methods_disabled()
 CategoricalIndex._add_comparison_methods()

pandas/tests/test_index.py

@@ -1488,6 +1488,19 @@ def test_construction_with_dtype(self):
         result = CategoricalIndex(idx, categories=idx, ordered=True)
         tm.assert_index_equal(result, expected, exact=True)
 
+    def test_disallow_set_ops(self):
+
+        # GH 10039
+        # set ops (+/-) raise TypeError
+        idx = pd.Index(pd.Categorical(['a', 'b']))
+
+        self.assertRaises(TypeError, lambda : idx - idx)
+        self.assertRaises(TypeError, lambda : idx + idx)
+        self.assertRaises(TypeError, lambda : idx - ['a','b'])
+        self.assertRaises(TypeError, lambda : idx + ['a','b'])
+        self.assertRaises(TypeError, lambda : ['a','b'] - idx)
+        self.assertRaises(TypeError, lambda : ['a','b'] + idx)
+
     def test_method_delegation(self):
 
         ci = CategoricalIndex(list('aabbca'), categories=list('cabdef'))
@@ -3882,6 +3895,12 @@ def test_difference(self):
         # - API change GH 8226
         with tm.assert_produces_warning():
             first - self.index[-3:]
+        with tm.assert_produces_warning():
+            self.index[-3:] - first
+        with tm.assert_produces_warning():
+            self.index[-3:] - first.tolist()
+        with tm.assert_produces_warning():
+            first.tolist() - self.index[-3:]
 
         expected = MultiIndex.from_tuples(sorted(self.index[:-3].values),
                                           sortorder=0,