Support NDFrame.shift with EAs

Uses take internally.

Closes pandas-dev#22386

Author: TomAugspurger

doc/source/whatsnew/v0.24.0.txt

@@ -444,6 +444,7 @@ ExtensionType Changes
   the ``ExtensionDtype`` has gained the method ``construct_array_type`` (:issue:`21185`)
 - The ``ExtensionArray`` constructor, ``_from_sequence`` now take the keyword arg ``copy=False`` (:issue:`21185`)
 - Bug in :meth:`Series.get` for ``Series`` using ``ExtensionArray`` and integer index (:issue:`21257`)
+- :meth:`~Series.shift` now works with extension arrays, rather than raising an AttributeError (:isseu:`22386`)
 - :meth:`Series.combine()` works correctly with :class:`~pandas.api.extensions.ExtensionArray` inside of :class:`Series` (:issue:`20825`)
 - :meth:`Series.combine()` with scalar argument now works for any function type (:issue:`21248`)
 -

pandas/core/internals/blocks.py

@@ -2061,6 +2061,24 @@ def interpolate(self, method='pad', axis=0, inplace=False, limit=None,
                                  limit=limit),
             placement=self.mgr_locs)
 
+    def shift(self, periods, axis=0, mgr=None):
+        # type: (int, int, Optional[BlockPlacement]) -> List[ExtensionBlock]
+        indexer = np.roll(np.arange(len(self)), periods)
+
+        if periods > 0:
+            indexer[:periods] = -1
+        else:
+            indexer[periods:] = -1
+
+        new_values = self.values.take(indexer, allow_fill=True)
+        return [self.make_block_same_class(new_values,
+                                           placement=self.mgr_locs,
+                                           ndim=self.ndim)]
+
+    @property
+    def _ftype(self):
+        return getattr(self.values, '_pandas_ftype', Block._ftype)
+
 
 class NumericBlock(Block):
     __slots__ = ()

pandas/tests/extension/base/methods.py

@@ -138,3 +138,28 @@ def test_combine_add(self, data_repeated):
         expected = pd.Series(
             orig_data1._from_sequence([a + val for a in list(orig_data1)]))
         self.assert_series_equal(result, expected)
+
+    @pytest.mark.parametrize('frame', [True, False])
+    @pytest.mark.parametrize('periods, indices', [
+        (-2, [2, 3, 4, -1, -1]),
+        (0, [0, 1, 2, 3, 4]),
+        (2, [-1, -1, 0, 1, 2]),
+    ])
+    def test_container_shift_negative(self, data, frame, periods, indices):
+        # https://github.com/pandas-dev/pandas/issues/22386
+        subset = data[:5]
+        data = pd.Series(subset, name='A')
+        expected = pd.Series(subset.take(indices, allow_fill=True), name='A')
+
+        if frame:
+            result = data.to_frame(name='A').assign(B=1).shift(periods)
+            expected = pd.concat([
+                expected,
+                pd.Series([1] * 5, name='B').shift(periods)
+            ], axis=1)
+            compare = tm.assert_frame_equal
+        else:
+            result = data.shift(periods)
+            compare = tm.assert_series_equal
+
+        compare(result, expected)