Drop & insert on subtypes of index return their subtypes

Author: max-sixty

doc/source/whatsnew/v0.17.0.txt

@@ -401,4 +401,5 @@ Bug Fixes
 - Bug in ``io.common.get_filepath_or_buffer`` which caused reading of valid S3 files to fail if the bucket also contained keys for which the user does not have read permission (:issue:`10604`)
 - Bug in vectorised setting of timestamp columns with python ``datetime.date`` and numpy ``datetime64`` (:issue:`10408`, :issue:`10412`)
 - Bug in ``pd.DataFrame`` when constructing an empty DataFrame with a string dtype (:issue:`9428`)
+- Bug in `Index` subtypes (such as `PeriodIndex`) not returning their own type for `.drop` and `.insert` methods
 

pandas/core/index.py

@@ -1548,8 +1548,16 @@ def sym_diff(self, other, result_name=None):
         other, result_name_update = self._convert_can_do_setop(other)
         if result_name is None:
             result_name = result_name_update
-        the_diff = sorted(set((self.difference(other)).union(other.difference(self))))
-        return Index(the_diff, name=result_name)
+        the_diff_sorted = sorted(set((self.difference(other)).union(other.difference(self))))
+        if isinstance(self, MultiIndex):
+            # multiindexes don't currently work well with _shallow_copy & can't be supplied a name
+            return Index(the_diff_sorted, **self._get_attributes_dict())
+        else:
+            # convert list to Index and pull values out - required for subtypes such as PeriodIndex
+            diff_array = Index(the_diff_sorted).values
+            return self._shallow_copy(diff_array, name=result_name)
+
+
 
     def get_loc(self, key, method=None):
         """
@@ -2527,7 +2535,7 @@ def delete(self, loc):
         -------
         new_index : Index
         """
-        return Index(np.delete(self._data, loc), name=self.name)
+        return self._shallow_copy(np.delete(self._data, loc))
 
     def insert(self, loc, item):
         """
@@ -2543,11 +2551,12 @@ def insert(self, loc, item):
         -------
         new_index : Index
         """
-        _self = np.asarray(self)
-        item_idx = Index([item], dtype=self.dtype).values
-        idx = np.concatenate(
-            (_self[:loc], item_idx, _self[loc:]))
-        return Index(idx, name=self.name)
+        indexes=[self[:loc],
+                 Index([item]),
+                 self[loc:]]
+
+        return indexes[0].append(indexes[1]).append(indexes[2])
+
 
     def drop(self, labels, errors='raise'):
         """

pandas/tests/test_index.py

@@ -396,6 +396,37 @@ def test_symmetric_diff(self):
                 with tm.assertRaisesRegexp(TypeError, msg):
                     result = first.sym_diff([1, 2, 3])
 
+    def test_insert_base(self):
+
+        for name, idx in compat.iteritems(self.indices):
+            result = idx[1:4]
+
+            if len(idx)>0:
+                #test 0th element
+                self.assertTrue(idx[0:4].equals(
+                    result.insert(0, idx[0])))
+
+    def test_delete_base(self):
+
+        for name, idx in compat.iteritems(self.indices):
+
+            if len(idx)>0:
+
+                expected = idx[1:]
+                result = idx.delete(0)
+                self.assertTrue(result.equals(expected))
+                self.assertEqual(result.name, expected.name)
+
+                expected = idx[:-1]
+                result = idx.delete(-1)
+                self.assertTrue(result.equals(expected))
+                self.assertEqual(result.name, expected.name)
+
+                with tm.assertRaises((IndexError, ValueError)):
+                    # either depending on numpy version
+                    result = idx.delete(len(idx))
+
+
     def test_equals_op(self):
         # GH9947, GH10637
         index_a = self.create_index()