BUG: should not pass empty list to from_tuples in diff

Author: wesm

pandas/core/index.py

@@ -1539,8 +1539,14 @@ def diff(self, other):
                               names=result_names)
 
         difference = sorted(set(self.values) - set(other.values))
-        return MultiIndex.from_tuples(difference, sortorder=0,
-                                      names=result_names)
+
+        if not difference:
+            return MultiIndex(levels=[[]]*self.nlevels,
+                              labels=[[]]*self.nlevels,
+                              names=result_names)
+        else:
+            return MultiIndex.from_tuples(difference, sortorder=0,
+                                          names=result_names)
 
     def _assert_can_do_setop(self, other):
         if not isinstance(other, MultiIndex):

pandas/tests/test_index.py

@@ -918,6 +918,10 @@ def test_diff(self):
         result = first - chunklet
         self.assertEqual(result.names, [None, None])
 
+        # empty, but non-equal
+        result = self.index - self.index.sortlevel(1)[0]
+        self.assert_(len(result) == 0)
+
     def test_argsort(self):
         result = self.index.argsort()
         expected = self.index.get_tuple_index().argsort()