REF: avoid accessing ._engine in Series/DataFrame (#41956)

Author: jbrockmendel

pandas/core/frame.py

@@ -158,7 +158,6 @@
 from pandas.core.indexers import check_key_length
 from pandas.core.indexes import base as ibase
 from pandas.core.indexes.api import (
-    CategoricalIndex,
     DatetimeIndex,
     Index,
     PeriodIndex,
@@ -3557,8 +3556,8 @@ def _get_value(self, index, col, takeable: bool = False) -> Scalar:
 
         Notes
         -----
-        Assumes that index and columns both have ax._index_as_unique;
-        caller is responsible for checking.
+        Assumes that both `self.index._index_as_unique` and
+        `self.columns._index_as_unique`; Caller is responsible for checking.
         """
         if takeable:
             series = self._ixs(col, axis=1)
@@ -3567,21 +3566,17 @@ def _get_value(self, index, col, takeable: bool = False) -> Scalar:
         series = self._get_item_cache(col)
         engine = self.index._engine
 
-        if isinstance(self.index, CategoricalIndex):
-            # Trying to use the engine fastpath may give incorrect results
-            #  if our categories are integers that dont match our codes
-            col = self.columns.get_loc(col)
-            index = self.index.get_loc(index)
-            return self._get_value(index, col, takeable=True)
+        if not isinstance(self.index, MultiIndex):
+            # CategoricalIndex: Trying to use the engine fastpath may give incorrect
+            #  results if our categories are integers that dont match our codes
+            # IntervalIndex: IntervalTree has no get_loc
+            row = self.index.get_loc(index)
+            return series._values[row]
 
-        try:
-            loc = engine.get_loc(index)
-            return series._values[loc]
-        except AttributeError:
-            # IntervalTree has no get_loc
-            col = self.columns.get_loc(col)
-            index = self.index.get_loc(index)
-            return self._get_value(index, col, takeable=True)
+        # For MultiIndex going through engine effectively restricts us to
+        #  same-length tuples; see test_get_set_value_no_partial_indexing
+        loc = engine.get_loc(index)
+        return series._values[loc]
 
     def __setitem__(self, key, value):
         key = com.apply_if_callable(key, self)
@@ -3816,8 +3811,7 @@ def _set_value(
                 return
 
             series = self._get_item_cache(col)
-            engine = self.index._engine
-            loc = engine.get_loc(index)
+            loc = self.index.get_loc(index)
             validate_numeric_casting(series.dtype, value)
 
             series._values[loc] = value

pandas/core/indexing.py

@@ -916,8 +916,7 @@ def __getitem__(self, key):
             key = tuple(list(x) if is_iterator(x) else x for x in key)
             key = tuple(com.apply_if_callable(x, self.obj) for x in key)
             if self._is_scalar_access(key):
-                with suppress(KeyError, IndexError):
-                    return self.obj._get_value(*key, takeable=self._takeable)
+                return self.obj._get_value(*key, takeable=self._takeable)
             return self._getitem_tuple(key)
         else:
             # we by definition only have the 0th axis
@@ -2187,7 +2186,7 @@ class _ScalarAccessIndexer(NDFrameIndexerBase):
     Access scalars quickly.
     """
 
-    def _convert_key(self, key, is_setter: bool = False):
+    def _convert_key(self, key):
         raise AbstractMethodError(self)
 
     def __getitem__(self, key):
@@ -2211,7 +2210,7 @@ def __setitem__(self, key, value):
 
         if not isinstance(key, tuple):
             key = _tuplify(self.ndim, key)
-        key = list(self._convert_key(key, is_setter=True))
+        key = list(self._convert_key(key))
         if len(key) != self.ndim:
             raise ValueError("Not enough indexers for scalar access (setting)!")
 
@@ -2222,7 +2221,7 @@ def __setitem__(self, key, value):
 class _AtIndexer(_ScalarAccessIndexer):
     _takeable = False
 
-    def _convert_key(self, key, is_setter: bool = False):
+    def _convert_key(self, key):
         """
         Require they keys to be the same type as the index. (so we don't
         fallback)
@@ -2233,10 +2232,6 @@ def _convert_key(self, key, is_setter: bool = False):
         if self.ndim == 1 and len(key) > 1:
             key = (key,)
 
-        # allow arbitrary setting
-        if is_setter:
-            return list(key)
-
         return key
 
     @property
@@ -2271,7 +2266,7 @@ def __setitem__(self, key, value):
 class _iAtIndexer(_ScalarAccessIndexer):
     _takeable = True
 
-    def _convert_key(self, key, is_setter: bool = False):
+    def _convert_key(self, key):
         """
         Require integer args. (and convert to label arguments)
         """

pandas/tests/indexing/test_iloc.py

@@ -596,7 +596,7 @@ def test_iloc_getitem_labelled_frame(self):
         assert result == exp
 
         # out-of-bounds exception
-        msg = "single positional indexer is out-of-bounds"
+        msg = "index 5 is out of bounds for axis 0 with size 4"
         with pytest.raises(IndexError, match=msg):
             df.iloc[10, 5]
 

pandas/tests/indexing/test_indexing.py

@@ -518,7 +518,7 @@ def test_string_slice_empty(self):
         with pytest.raises(KeyError, match="'2011'"):
             df["2011"]
 
-        with pytest.raises(KeyError, match="'2011'"):
+        with pytest.raises(KeyError, match="^0$"):
             df.loc["2011", 0]
 
     def test_astype_assignment(self):