BUG: fix construction of NonConsolidatableBlock with inconsistent ndim (pandas-dev#27786)

Author: jorisvandenbossche

pandas/core/internals/blocks.py

@@ -263,6 +263,8 @@ def make_block_same_class(self, values, placement=None, ndim=None, dtype=None):
             )
         if placement is None:
             placement = self.mgr_locs
+        if ndim is None:
+            ndim = self.ndim
         return make_block(
             values, placement=placement, ndim=ndim, klass=self.__class__, dtype=dtype
         )

pandas/tests/extension/base/getitem.py

@@ -260,3 +260,9 @@ def test_reindex_non_na_fill_value(self, data_missing):
         expected = pd.Series(data_missing._from_sequence([na, valid, valid]))
 
         self.assert_series_equal(result, expected)
+
+    def test_loc_len1(self, data):
+        # see GH-27785 take_nd with indexer of len 1 resulting in wrong ndim
+        df = pd.DataFrame({"A": data})
+        res = df.loc[[0], "A"]
+        assert res._data._block.ndim == 1