REF: implement _split_op_result (pandas-dev#31027)

Author: jbrockmendel

pandas/core/internals/blocks.py

@@ -362,13 +362,17 @@ def delete(self, loc):
         self.values = np.delete(self.values, loc, 0)
         self.mgr_locs = self.mgr_locs.delete(loc)
 
-    def apply(self, func, **kwargs):
+    def apply(self, func, **kwargs) -> List["Block"]:
         """ apply the function to my values; return a block if we are not
         one
         """
         with np.errstate(all="ignore"):
             result = func(self.values, **kwargs)
 
+        return self._split_op_result(result)
+
+    def _split_op_result(self, result) -> List["Block"]:
+        # See also: split_and_operate
         if is_extension_array_dtype(result) and result.ndim > 1:
             # if we get a 2D ExtensionArray, we need to split it into 1D pieces
             nbs = []
@@ -382,7 +386,7 @@ def apply(self, func, **kwargs):
         if not isinstance(result, Block):
             result = self.make_block(values=_block_shape(result, ndim=self.ndim))
 
-        return result
+        return [result]
 
     def fillna(self, value, limit=None, inplace=False, downcast=None):
         """ fillna on the block with the value. If we fail, then convert to

pandas/core/internals/managers.py

@@ -1341,7 +1341,7 @@ def _slice_take_blocks_ax0(self, slice_or_indexer, fill_tuple=None):
                     # only one item and each mgr loc is a copy of that single
                     # item.
                     for mgr_loc in mgr_locs:
-                        newblk = blk.copy(deep=True)
+                        newblk = blk.copy(deep=False)
                         newblk.mgr_locs = slice(mgr_loc, mgr_loc + 1)
                         blocks.append(newblk)