clean-up fast_xs workarounds now it returns a SingleBlockManager

Author: jorisvandenbossche

pandas/core/frame.py

@@ -30,7 +30,6 @@
     overload,
 )
 import warnings
-import weakref
 
 import numpy as np
 import numpy.ma as ma
@@ -3493,10 +3492,6 @@ def _ixs(self, i: int, axis: int = 0):
                 self
             )
             result._set_is_copy(self, copy=copy)
-            # TODO(CoW) cleaner solution (eg let fast_xs return a SingleBM?)
-            if not copy and isinstance(self._mgr, BlockManager):
-                # assert len(self._mgr.blocks) == 1
-                result._mgr.refs = [weakref.ref(self._mgr.blocks[0])]
             return result
 
         # icol

pandas/core/generic.py

@@ -3820,11 +3820,6 @@ class   animal   locomotion
             result = self._constructor_sliced(
                 new_mgr, name=self.index[loc]
             ).__finalize__(self)
-            # TODO(CoW) cleaner solution (eg let fast_xs return a SingleBM?)
-            if isinstance(self._mgr, BlockManager) and len(self._mgr.blocks) == 1:
-                # in the case of a single block, new_values is a view
-                result._mgr.refs = [weakref.ref(self._mgr.blocks[0])]
-
         elif is_scalar(loc):
             result = self.iloc[:, slice(loc, loc + 1)]
         elif axis == 1:

pandas/core/internals/managers.py

@@ -1065,7 +1065,9 @@ def fast_xs(self, loc: int) -> SingleBlockManager:
         if len(self.blocks) == 1:
             result = self.blocks[0].iget((slice(None), loc))
             block = new_block(result, placement=slice(0, len(result)), ndim=1)
-            return SingleBlockManager(block, self.axes[0])
+            # in the case of a single block, the new block is a view
+            ref = weakref.ref(self.blocks[0])
+            return SingleBlockManager(block, self.axes[0], [ref])
 
         dtype = interleaved_dtype([blk.dtype for blk in self.blocks])