BUG: provide deprecation warnings when using setlike operations on Indexes and lists (for +/-) (GH10038)

Author: jreback

pandas/core/index.py

@@ -1179,18 +1179,20 @@ def argsort(self, *args, **kwargs):
         return result.argsort(*args, **kwargs)
 
     def __add__(self, other):
-        if isinstance(other, Index):
+        if com.is_list_like(other):
             warnings.warn("using '+' to provide set union with Indexes is deprecated, "
                           "use '|' or .union()",FutureWarning)
+        if isinstance(other, Index):
             return self.union(other)
         return Index(np.array(self) + other)
     __iadd__ = __add__
+    __radd__ = __add__
 
     def __sub__(self, other):
-        if isinstance(other, Index):
-            warnings.warn("using '-' to provide set differences with Indexes is deprecated, "
-                          "use .difference()",FutureWarning)
+        warnings.warn("using '-' to provide set differences with Indexes is deprecated, "
+                      "use .difference()",FutureWarning)
         return self.difference(other)
+    __rsub__ = __sub__
 
     def __and__(self, other):
         return self.intersection(other)
@@ -2481,8 +2483,8 @@ def invalid_op(self, other=None):
             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__')
+        cls.__add__ = cls.__radd__ = __iadd__ = _make_invalid_op('__add__')
+        cls.__sub__ = cls.__rsub__ = __isub__ = _make_invalid_op('__sub__')
 
     @classmethod
     def _add_numeric_methods_disabled(cls):

pandas/tests/test_index.py

@@ -686,6 +686,10 @@ def test_add(self):
         # - API change GH 8226
         with tm.assert_produces_warning():
             self.strIndex + self.strIndex
+        with tm.assert_produces_warning():
+            self.strIndex + self.strIndex.tolist()
+        with tm.assert_produces_warning():
+            self.strIndex.tolist() + self.strIndex
 
         firstCat = self.strIndex.union(self.dateIndex)
         secondCat = self.strIndex.union(self.strIndex)
@@ -772,6 +776,7 @@ def test_difference(self):
         assertRaisesRegexp(TypeError, "iterable", first.difference, 0.5)
 
     def test_symmetric_diff(self):
+
         # smoke
         idx1 = Index([1, 2, 3, 4], name='idx1')
         idx2 = Index([2, 3, 4, 5])
@@ -819,7 +824,7 @@ def test_symmetric_diff(self):
 
         # other isn't iterable
         with tm.assertRaises(TypeError):
-            Index(idx1,dtype='object') - 1
+            Index(idx1,dtype='object').difference(1)
 
     def test_is_numeric(self):
         self.assertFalse(self.dateIndex.is_numeric())