REF: better names, stricter typing for mgr/block indexing methods

pandas/_libs/internals.pyi

@@ -10,7 +10,7 @@ import numpy as np
 
 from pandas._typing import (
     ArrayLike,
-    T,
+    Self,
     npt,
 )
 
@@ -76,12 +76,12 @@ class SharedBlock:
 class NumpyBlock(SharedBlock):
     values: np.ndarray
     @final
-    def getitem_block_index(self: T, slicer: slice) -> T: ...
+    def slice_block_rows(self, slicer: slice) -> Self: ...
 
 class NDArrayBackedBlock(SharedBlock):
     values: NDArrayBackedExtensionArray
     @final
-    def getitem_block_index(self: T, slicer: slice) -> T: ...
+    def slice_block_rows(self, slicer: slice) -> Self: ...
 
 class Block(SharedBlock): ...
 
@@ -95,7 +95,7 @@ class BlockManager:
     def __init__(
         self, blocks: tuple[B, ...], axes: list[Index], verify_integrity=...
     ) -> None: ...
-    def get_slice(self: T, slobj: slice, axis: int = ...) -> T: ...
+    def get_slice(self, slobj: slice, axis: int = ...) -> Self: ...
     def _rebuild_blknos_and_blklocs(self) -> None: ...
 
 class BlockValuesRefs:

pandas/_libs/internals.pyx

@@ -715,7 +715,7 @@ cdef class NumpyBlock(SharedBlock):
         #  set placement, ndim and refs
         self.values = values
 
-    cpdef NumpyBlock getitem_block_index(self, slice slicer):
+    cpdef NumpyBlock slice_block_rows(self, slice slicer):
         """
         Perform __getitem__-like specialized to slicing along index.
 
@@ -743,7 +743,7 @@ cdef class NDArrayBackedBlock(SharedBlock):
         #  set placement, ndim and refs
         self.values = values
 
-    cpdef NDArrayBackedBlock getitem_block_index(self, slice slicer):
+    cpdef NDArrayBackedBlock slice_block_rows(self, slice slicer):
         """
         Perform __getitem__-like specialized to slicing along index.
 
@@ -899,15 +899,15 @@ cdef class BlockManager:
     # -------------------------------------------------------------------
     # Indexing
 
-    cdef BlockManager _get_index_slice(self, slice slobj):
+    cdef BlockManager _slice_mgr_rows(self, slice slobj):
         cdef:
             SharedBlock blk, nb
             BlockManager mgr
             ndarray blknos, blklocs
 
         nbs = []
         for blk in self.blocks:
-            nb = blk.getitem_block_index(slobj)
+            nb = blk.slice_block_rows(slobj)
             nbs.append(nb)
 
         new_axes = [self.axes[0], self.axes[1]._getitem_slice(slobj)]
@@ -926,7 +926,7 @@ cdef class BlockManager:
         if axis == 0:
             new_blocks = self._slice_take_blocks_ax0(slobj)
         elif axis == 1:
-            return self._get_index_slice(slobj)
+            return self._slice_mgr_rows(slobj)
         else:
             raise IndexError("Requested axis not found in manager")
 

pandas/core/internals/array_manager.py

@@ -1275,7 +1275,7 @@ def get_slice(self, slobj: slice, axis: AxisInt = 0) -> SingleArrayManager:
         new_index = self.index._getitem_slice(slobj)
         return type(self)([new_array], [new_index], verify_integrity=False)
 
-    def getitem_mgr(self, indexer) -> SingleArrayManager:
+    def get_rows_with_mask(self, indexer: npt.NDArray[np.bool_]) -> SingleArrayManager:
         new_array = self.array[indexer]
         new_index = self.index[indexer]
         return type(self)([new_array], [new_index])

pandas/core/internals/blocks.py

@@ -36,6 +36,7 @@
     FillnaOptions,
     IgnoreRaise,
     QuantileInterpolation,
+    Self,
     Shape,
     npt,
 )
@@ -259,36 +260,41 @@ def __len__(self) -> int:
         return len(self.values)
 
     @final
-    def getitem_block(self, slicer: slice | npt.NDArray[np.intp]) -> Block:
+    def slice_block_columns(self, slc: slice) -> Self:
+        """
+        Perform __getitem__-like, return result as block.
+        """
+        new_mgr_locs = self._mgr_locs[slc]
+
+        new_values = self._slice(slc)
+        refs = self.refs
+        return type(self)(new_values, new_mgr_locs, self.ndim, refs=refs)
+
+    @final
+    def take_block_columns(self, indices: npt.NDArray[np.intp]) -> Self:
         """
         Perform __getitem__-like, return result as block.
 
         Only supports slices that preserve dimensionality.
         """
-        # Note: the only place where we are called with ndarray[intp]
-        #  is from internals.concat, and we can verify that never happens
-        #  with 1-column blocks, i.e. never for ExtensionBlock.
+        # Note: only called from is from internals.concat, and we can verify
+        #  that never happens with 1-column blocks, i.e. never for ExtensionBlock.
 
-        new_mgr_locs = self._mgr_locs[slicer]
+        new_mgr_locs = self._mgr_locs[indices]
 
-        new_values = self._slice(slicer)
-        refs = self.refs if isinstance(slicer, slice) else None
-        return type(self)(new_values, new_mgr_locs, self.ndim, refs=refs)
+        new_values = self._slice(indices)
+        return type(self)(new_values, new_mgr_locs, self.ndim, refs=None)
 
     @final
     def getitem_block_columns(
         self, slicer: slice, new_mgr_locs: BlockPlacement
-    ) -> Block:
+    ) -> Self:
         """
         Perform __getitem__-like, return result as block.
 
         Only supports slices that preserve dimensionality.
         """
         new_values = self._slice(slicer)
-
-        if new_values.ndim != self.values.ndim:
-            raise ValueError("Only same dim slicing is allowed")
-
         return type(self)(new_values, new_mgr_locs, self.ndim, refs=self.refs)
 
     @final
@@ -1997,7 +2003,7 @@ def _slice(
         -------
         ExtensionArray
         """
-        # Notes: ndarray[bool] is only reachable when via getitem_mgr, which
+        # Notes: ndarray[bool] is only reachable when via get_rows_with_mask, which
         #  is only for Series, i.e. self.ndim == 1.
 
         # return same dims as we currently have
@@ -2023,7 +2029,7 @@ def _slice(
         return self.values[slicer]
 
     @final
-    def getitem_block_index(self, slicer: slice) -> ExtensionBlock:
+    def slice_block_rows(self, slicer: slice) -> Self:
         """
         Perform __getitem__-like specialized to slicing along index.
         """

pandas/core/internals/concat.py

@@ -328,7 +328,10 @@ def _get_block_for_concat_plan(
         slc = lib.maybe_indices_to_slice(ax0_blk_indexer, max_len)
         # TODO: in all extant test cases 2023-04-08 we have a slice here.
         #  Will this always be the case?
-        nb = blk.getitem_block(slc)
+        if isinstance(slc, slice):
+            nb = blk.slice_block_columns(slc)
+        else:
+            nb = blk.take_block_columns(slc)
 
     # assert nb.shape == (len(bp), mgr.shape[1])
     return nb

pandas/core/internals/managers.py

@@ -54,7 +54,6 @@
 import pandas.core.algorithms as algos
 from pandas.core.arrays import DatetimeArray
 from pandas.core.arrays._mixins import NDArrayBackedExtensionArray
-import pandas.core.common as com
 from pandas.core.construction import (
     ensure_wrapped_if_datetimelike,
     extract_array,
@@ -1872,7 +1871,7 @@ def concat_horizontal(cls, mgrs: list[Self], axes: list[Index]) -> Self:
                 # We need to do getitem_block here otherwise we would be altering
                 #  blk.mgr_locs in place, which would render it invalid. This is only
                 #  relevant in the copy=False case.
-                nb = blk.getitem_block(slice(None))
+                nb = blk.slice_block_columns(slice(None))
                 nb._mgr_locs = nb._mgr_locs.add(offset)
                 blocks.append(nb)
 
@@ -2018,21 +2017,12 @@ def _blklocs(self):
         """compat with BlockManager"""
         return None
 
-    def getitem_mgr(self, indexer: slice | np.ndarray) -> SingleBlockManager:
+    def get_rows_with_mask(self, indexer: npt.NDArray[np.bool_]) -> Self:
         # similar to get_slice, but not restricted to slice indexer
         blk = self._block
-        if (
-            using_copy_on_write()
-            and isinstance(indexer, np.ndarray)
-            and len(indexer) > 0
-            and com.is_bool_indexer(indexer)
-            and indexer.all()
-        ):
+        if using_copy_on_write() and len(indexer) > 0 and indexer.all():
             return type(self)(blk.copy(deep=False), self.index)
-        array = blk._slice(indexer)
-        if array.ndim > 1:
-            # This will be caught by Series._get_values
-            raise ValueError("dimension-expanding indexing not allowed")
+        array = blk.values[indexer]
 
         bp = BlockPlacement(slice(0, len(array)))
         # TODO(CoW) in theory only need to track reference if new_array is a view
@@ -2048,7 +2038,7 @@ def get_slice(self, slobj: slice, axis: AxisInt = 0) -> SingleBlockManager:
             raise IndexError("Requested axis not found in manager")
 
         blk = self._block
-        array = blk._slice(slobj)
+        array = blk.values[slobj]
         bp = BlockPlacement(slice(0, len(array)))
         # TODO this method is only used in groupby SeriesSplitter at the moment,
         # so passing refs is not yet covered by the tests

pandas/core/series.py

@@ -998,7 +998,7 @@ def __getitem__(self, key):
         if com.is_bool_indexer(key):
             key = check_bool_indexer(self.index, key)
             key = np.asarray(key, dtype=bool)
-            return self._get_values(key)
+            return self._get_rows_with_mask(key)
 
         return self._get_with(key)
 
@@ -1054,8 +1054,8 @@ def _get_values_tuple(self, key: tuple):
             new_ser._mgr.add_references(self._mgr)  # type: ignore[arg-type]
         return new_ser.__finalize__(self)
 
-    def _get_values(self, indexer: slice | npt.NDArray[np.bool_]) -> Series:
-        new_mgr = self._mgr.getitem_mgr(indexer)
+    def _get_rows_with_mask(self, indexer: npt.NDArray[np.bool_]) -> Series:
+        new_mgr = self._mgr.get_rows_with_mask(indexer)
         return self._constructor(new_mgr, fastpath=True).__finalize__(self)
 
     def _get_value(self, label, takeable: bool = False):

pandas/tests/extension/base/getitem.py

@@ -285,7 +285,7 @@ def test_getitem_slice(self, data):
         assert isinstance(result, type(data))
 
     def test_getitem_ellipsis_and_slice(self, data):
-        # GH#40353 this is called from getitem_block_index
+        # GH#40353 this is called from slice_block_rows
         result = data[..., :]
         self.assert_extension_array_equal(result, data)
 

pandas/tests/internals/test_internals.py

@@ -942,12 +942,17 @@ def assert_slice_ok(mgr, axis, slobj):
 
             if isinstance(slobj, slice):
                 sliced = mgr.get_slice(slobj, axis=axis)
-            elif mgr.ndim == 1 and axis == 0:
-                sliced = mgr.getitem_mgr(slobj)
+            elif (
+                mgr.ndim == 1
+                and axis == 0
+                and isinstance(slobj, np.ndarray)
+                and slobj.dtype == bool
+            ):
+                sliced = mgr.get_rows_with_mask(slobj)
             else:
                 # BlockManager doesn't support non-slice, SingleBlockManager
                 #  doesn't support axis > 0
-                return
+                raise TypeError(slobj)
 
             mat_slobj = (slice(None),) * axis + (slobj,)
             tm.assert_numpy_array_equal(
@@ -978,14 +983,6 @@ def assert_slice_ok(mgr, axis, slobj):
                         mgr, ax, np.array([True, True, False], dtype=np.bool_)
                     )
 
-                # fancy indexer
-                assert_slice_ok(mgr, ax, [])
-                assert_slice_ok(mgr, ax, list(range(mgr.shape[ax])))
-
-                if mgr.shape[ax] >= 3:
-                    assert_slice_ok(mgr, ax, [0, 1, 2])
-                    assert_slice_ok(mgr, ax, [-1, -2, -3])
-
     @pytest.mark.parametrize("mgr", MANAGERS)
     def test_take(self, mgr):
         def assert_take_ok(mgr, axis, indexer):