return empty MultiIndex for symmetrical difference on equal MultiIndexes

doc/source/whatsnew/v0.20.2.txt

@@ -38,6 +38,7 @@ Bug Fixes
 ~~~~~~~~~
 
 - Bug in using ``pathlib.Path`` or ``py.path.local`` objects with io functions (:issue:`16291`)
+- Bug in ``Index`` calling symmetric_difference() on two equal multiindices results in a TypeError (:issue `13490`)
 - Bug in ``DataFrame.update()`` with ``overwrite=False`` and ``NaN values`` (:issue:`15593`)
 
 

pandas/core/indexes/multi.py

@@ -419,6 +419,11 @@ def _shallow_copy_with_infer(self, values=None, **kwargs):
     @Appender(_index_shared_docs['_shallow_copy'])
     def _shallow_copy(self, values=None, **kwargs):
         if values is not None:
+            # On equal MultiIndexes the difference is empty.
+            # Therefore, an empty MultiIndex is returned GH13490
+            if len(values) == 0:
+                return MultiIndex(levels=[[] for _ in range(self.nlevels)],
+                                  labels=[[] for _ in range(self.nlevels)], **kwargs)
             if 'name' in kwargs:
                 kwargs['names'] = kwargs.pop('name', None)
             # discards freq

pandas/tests/indexes/test_base.py

@@ -188,7 +188,6 @@ def test_constructor_ndarray_like(self):
         # it should be possible to convert any object that satisfies the numpy
         # ndarray interface directly into an Index
         class ArrayLike(object):
-
             def __init__(self, array):
                 self.array = array
 
@@ -246,7 +245,6 @@ def test_index_ctor_infer_nan_nat(self):
                      [np.timedelta64('nat'), np.nan],
                      [pd.NaT, np.timedelta64('nat')],
                      [np.timedelta64('nat'), pd.NaT]]:
-
             tm.assert_index_equal(Index(data), exp)
             tm.assert_index_equal(Index(np.array(data, dtype=object)), exp)
 
@@ -936,6 +934,14 @@ def test_symmetric_difference(self):
         assert tm.equalContents(result, expected)
         assert result.name == 'new_name'
 
+    def test_symmetric_difference_on_equal_multiindex(self):
+        # GH13490
+        idx1 = MultiIndex.from_tuples(self.tuples)
+        idx2 = MultiIndex.from_tuples(self.tuples)
+        result = idx1.symmetric_difference(idx2)
+        expected = MultiIndex(levels=[[], []], labels=[[], []])
+        assert tm.assert_index_equal(result, expected)
+
     def test_is_numeric(self):
         assert not self.dateIndex.is_numeric()
         assert not self.strIndex.is_numeric()

pandas/tests/indexing/test_multiindex.py

@@ -697,6 +697,17 @@ def test_multiindex_slice_first_level(self):
                                 index=range(30, 71))
         tm.assert_frame_equal(result, expected)
 
+    def test_multiindex_symmetric_difference(self):
+        # GH 13490
+        idx = MultiIndex.from_product([['a', 'b'], ['A', 'B']],
+                                      names=['a', 'b'])
+        result = idx ^ idx
+        assert result.names == idx.names
+
+        idx2 = idx.copy().rename(['A', 'B'])
+        result = idx ^ idx2
+        assert result.names == [None, None]
+
 
 class TestMultiIndexSlicers(object):