REF: avoid access to _mgr.blocks -> _mgr._is_single_block (pandas-dev#37155)

Author: jorisvandenbossche

pandas/core/generic.py

@@ -5474,7 +5474,7 @@ def _consolidate(self):
 
     @property
     def _is_mixed_type(self) -> bool_t:
-        if len(self._mgr.blocks) == 1:
+        if self._mgr.is_single_block:
             return False
 
         if self._mgr.any_extension_types:
@@ -6262,7 +6262,7 @@ def fillna(
         axis = self._get_axis_number(axis)
 
         if value is None:
-            if len(self._mgr.blocks) > 1 and axis == 1:
+            if not self._mgr.is_single_block and axis == 1:
                 if inplace:
                     raise NotImplementedError()
                 result = self.T.fillna(method=method, limit=limit).T

pandas/core/indexing.py

@@ -1540,7 +1540,7 @@ def _setitem_with_indexer(self, indexer, value):
         info_axis = self.obj._info_axis_number
 
         # maybe partial set
-        take_split_path = len(self.obj._mgr.blocks) > 1
+        take_split_path = not self.obj._mgr.is_single_block
 
         # if there is only one block/type, still have to take split path
         # unless the block is one-dimensional or it can hold the value

pandas/core/internals/concat.py

@@ -115,7 +115,7 @@ def _get_mgr_concatenation_plan(mgr, indexers):
         blklocs = algos.take_1d(mgr.blklocs, ax0_indexer, fill_value=-1)
     else:
 
-        if mgr._is_single_block:
+        if mgr.is_single_block:
             blk = mgr.blocks[0]
             return [(blk.mgr_locs, JoinUnit(blk, mgr_shape, indexers))]
 

pandas/core/internals/managers.py

@@ -225,7 +225,7 @@ def set_axis(self, axis: int, new_labels: Index) -> None:
         self.axes[axis] = new_labels
 
     @property
-    def _is_single_block(self) -> bool:
+    def is_single_block(self) -> bool:
         # Assumes we are 2D; overridden by SingleBlockManager
         return len(self.blocks) == 1
 
@@ -833,7 +833,7 @@ def as_array(
         # mutating the original object
         copy = copy or na_value is not lib.no_default
 
-        if self._is_single_block:
+        if self.is_single_block:
             blk = self.blocks[0]
             if blk.is_extension:
                 # Avoid implicit conversion of extension blocks to object
@@ -1313,7 +1313,7 @@ def _slice_take_blocks_ax0(
             slice_or_indexer, self.shape[0], allow_fill=allow_fill
         )
 
-        if self._is_single_block:
+        if self.is_single_block:
             blk = self.blocks[0]
 
             if sl_type in ("slice", "mask"):
@@ -1503,7 +1503,7 @@ class SingleBlockManager(BlockManager):
     _is_consolidated = True
     _known_consolidated = True
     __slots__ = ()
-    _is_single_block = True
+    is_single_block = True
 
     def __init__(
         self,