TYP: enforce tighter inputs on SingleBlockManager (#33092)

Author: jbrockmendel

doc/source/whatsnew/v1.1.0.rst

@@ -253,6 +253,7 @@ Deprecations
 - Setting values with ``.loc`` using a positional slice is deprecated and will raise in a future version.  Use ``.loc`` with labels or ``.iloc`` with positions instead (:issue:`31840`)
 - :meth:`DataFrame.to_dict` has deprecated accepting short names for ``orient`` in future versions (:issue:`32515`)
 - :meth:`Categorical.to_dense` is deprecated and will be removed in a future version, use ``np.asarray(cat)`` instead (:issue:`32639`)
+- The ``fastpath`` keyword in the ``SingleBlockManager`` constructor is deprecated and will be removed in a future version (:issue:`33092`)
 
 .. ---------------------------------------------------------------------------
 

pandas/core/internals/managers.py

@@ -4,6 +4,7 @@
 import operator
 import re
 from typing import Dict, List, Optional, Sequence, Tuple, TypeVar, Union
+import warnings
 
 import numpy as np
 
@@ -540,9 +541,7 @@ def get_axe(block, qs, axes):
             values = values.take(indexer)
 
         return SingleBlockManager(
-            make_block(values, ndim=1, placement=np.arange(len(values))),
-            axes[0],
-            fastpath=True,
+            make_block(values, ndim=1, placement=np.arange(len(values))), axes[0],
         )
 
     def isna(self, func) -> "BlockManager":
@@ -1001,7 +1000,6 @@ def iget(self, i: int) -> "SingleBlockManager":
                 values, placement=slice(0, len(values)), ndim=1
             ),
             self.axes[1],
-            fastpath=True,
         )
 
     def delete(self, item):
@@ -1509,25 +1507,22 @@ class SingleBlockManager(BlockManager):
     def __init__(
         self,
         block: Block,
-        axis: Union[Index, List[Index]],
+        axis: Index,
         do_integrity_check: bool = False,
-        fastpath: bool = False,
+        fastpath=lib.no_default,
     ):
         assert isinstance(block, Block), type(block)
+        assert isinstance(axis, Index), type(axis)
+
+        if fastpath is not lib.no_default:
+            warnings.warn(
+                "The `fastpath` keyword is deprecated and will be removed "
+                "in a future version.",
+                FutureWarning,
+                stacklevel=2,
+            )
 
-        if isinstance(axis, list):
-            if len(axis) != 1:
-                raise ValueError(
-                    "cannot create SingleBlockManager with more than 1 axis"
-                )
-            axis = axis[0]
-
-        # passed from constructor, single block, single axis
-        if fastpath:
-            self.axes = [axis]
-        else:
-            self.axes = [ensure_index(axis)]
-
+        self.axes = [axis]
         self.blocks = tuple([block])
 
     @classmethod
@@ -1539,15 +1534,15 @@ def from_blocks(
         """
         assert len(blocks) == 1
         assert len(axes) == 1
-        return cls(blocks[0], axes[0], do_integrity_check=False, fastpath=True)
+        return cls(blocks[0], axes[0], do_integrity_check=False)
 
     @classmethod
     def from_array(cls, array: ArrayLike, index: Index) -> "SingleBlockManager":
         """
         Constructor for if we have an array that is not yet a Block.
         """
         block = make_block(array, placement=slice(0, len(index)), ndim=1)
-        return cls(block, index, fastpath=True)
+        return cls(block, index)
 
     def _post_setstate(self):
         pass
@@ -1573,7 +1568,7 @@ def get_slice(self, slobj: slice, axis: int = 0) -> "SingleBlockManager":
         blk = self._block
         array = blk._slice(slobj)
         block = blk.make_block_same_class(array, placement=range(len(array)))
-        return type(self)(block, self.index[slobj], fastpath=True)
+        return type(self)(block, self.index[slobj])
 
     @property
     def index(self) -> Index:
@@ -1627,7 +1622,9 @@ def fast_xs(self, loc):
         """
         raise NotImplementedError("Use series._values[loc] instead")
 
-    def concat(self, to_concat, new_axis: Index) -> "SingleBlockManager":
+    def concat(
+        self, to_concat: List["SingleBlockManager"], new_axis: Index
+    ) -> "SingleBlockManager":
         """
         Concatenate a list of SingleBlockManagers into a single
         SingleBlockManager.

pandas/core/reshape/concat.py

@@ -458,7 +458,7 @@ def get_result(self):
                 name = com.consensus_name_attr(self.objs)
 
                 mgr = self.objs[0]._data.concat(
-                    [x._data for x in self.objs], self.new_axes
+                    [x._data for x in self.objs], self.new_axes[0]
                 )
                 cons = self.objs[0]._constructor
                 return cons(mgr, name=name).__finalize__(self, method="concat")

pandas/core/series.py

@@ -971,9 +971,7 @@ def _get_values_tuple(self, key):
 
     def _get_values(self, indexer):
         try:
-            return self._constructor(
-                self._data.get_slice(indexer), fastpath=True
-            ).__finalize__(self)
+            return self._constructor(self._data.get_slice(indexer)).__finalize__(self)
         except ValueError:
             # mpl compat if we look up e.g. ser[:, np.newaxis];
             #  see tests.series.timeseries.test_mpl_compat_hack

pandas/tests/internals/test_internals.py

@@ -135,7 +135,7 @@ def create_single_mgr(typestr, num_rows=None):
 
     return SingleBlockManager(
         create_block(typestr, placement=slice(0, num_rows), item_shape=()),
-        np.arange(num_rows),
+        Index(np.arange(num_rows)),
     )
 
 
@@ -1297,3 +1297,11 @@ def test_interleave_non_unique_cols():
     assert df_unique.values.shape == df.values.shape
     tm.assert_numpy_array_equal(df_unique.values[0], df.values[0])
     tm.assert_numpy_array_equal(df_unique.values[1], df.values[1])
+
+
+def test_single_block_manager_fastpath_deprecated():
+    # GH#33092
+    ser = pd.Series(range(3))
+    blk = ser._data.blocks[0]
+    with tm.assert_produces_warning(FutureWarning):
+        SingleBlockManager(blk, ser.index, fastpath=True)