CLN: Prune unnecessary indexing code (pandas-dev#27576)

Author: jbrockmendel

pandas/core/frame.py

@@ -94,12 +94,9 @@
 )
 from pandas.core.indexes import base as ibase
 from pandas.core.indexes.datetimes import DatetimeIndex
+from pandas.core.indexes.multi import maybe_droplevels
 from pandas.core.indexes.period import PeriodIndex
-from pandas.core.indexing import (
-    check_bool_indexer,
-    convert_to_index_sliceable,
-    maybe_droplevels,
-)
+from pandas.core.indexing import check_bool_indexer, convert_to_index_sliceable
 from pandas.core.internals import BlockManager
 from pandas.core.internals.construction import (
     arrays_to_mgr,
@@ -2794,8 +2791,6 @@ def _ixs(self, i: int, axis: int = 0):
         if axis == 0:
             label = self.index[i]
             new_values = self._data.fast_xs(i)
-            if is_scalar(new_values):
-                return new_values
 
             # if we are a copy, mark as such
             copy = isinstance(new_values, np.ndarray) and new_values.base is None
@@ -2906,6 +2901,7 @@ def _getitem_bool_array(self, key):
         return self.take(indexer, axis=0)
 
     def _getitem_multilevel(self, key):
+        # self.columns is a MultiIndex
         loc = self.columns.get_loc(key)
         if isinstance(loc, (slice, Series, np.ndarray, Index)):
             new_columns = self.columns[loc]

pandas/core/generic.py

@@ -3296,11 +3296,8 @@ def _maybe_update_cacher(self, clear=False, verify_is_copy=True):
         if clear:
             self._clear_item_cache()
 
-    def _clear_item_cache(self, i=None):
-        if i is not None:
-            self._item_cache.pop(i, None)
-        else:
-            self._item_cache.clear()
+    def _clear_item_cache(self):
+        self._item_cache.clear()
 
     # ----------------------------------------------------------------------
     # Indexing Methods
@@ -3559,27 +3556,8 @@ class   animal   locomotion
 
     _xs = xs  # type: Callable
 
-    def get(self, key, default=None):
-        """
-        Get item from object for given key (ex: DataFrame column).
-
-        Returns default value if not found.
-
-        Parameters
-        ----------
-        key : object
-
-        Returns
-        -------
-        value : same type as items contained in object
-        """
-        try:
-            return self[key]
-        except (KeyError, ValueError, IndexError):
-            return default
-
     def __getitem__(self, item):
-        return self._get_item_cache(item)
+        raise AbstractMethodError(self)
 
     def _get_item_cache(self, item):
         """Return the cached item, item represents a label indexer."""
@@ -3770,6 +3748,25 @@ def __delitem__(self, key):
     # ----------------------------------------------------------------------
     # Unsorted
 
+    def get(self, key, default=None):
+        """
+        Get item from object for given key (ex: DataFrame column).
+
+        Returns default value if not found.
+
+        Parameters
+        ----------
+        key : object
+
+        Returns
+        -------
+        value : same type as items contained in object
+        """
+        try:
+            return self[key]
+        except (KeyError, ValueError, IndexError):
+            return default
+
     @property
     def _is_view(self):
         """Return boolean indicating if self is view of another array """

pandas/core/indexes/multi.py

@@ -1470,9 +1470,6 @@ def dropna(self, how="any"):
         return self.copy(codes=new_codes, deep=True)
 
     def get_value(self, series, key):
-        # somewhat broken encapsulation
-        from pandas.core.indexing import maybe_droplevels
-
         # Label-based
         s = com.values_from_object(series)
         k = com.values_from_object(key)
@@ -2709,7 +2706,7 @@ def _maybe_to_slice(loc):
 
         return _maybe_to_slice(loc) if len(loc) != stop - start else slice(start, stop)
 
-    def get_loc_level(self, key, level=0, drop_level=True):
+    def get_loc_level(self, key, level=0, drop_level: bool = True):
         """
         Get both the location for the requested label(s) and the
         resulting sliced index.
@@ -2750,7 +2747,8 @@ def get_loc_level(self, key, level=0, drop_level=True):
         (1, None)
         """
 
-        def maybe_droplevels(indexer, levels, drop_level):
+        # different name to distinguish from maybe_droplevels
+        def maybe_mi_droplevels(indexer, levels, drop_level: bool):
             if not drop_level:
                 return self[indexer]
             # kludgearound
@@ -2780,7 +2778,7 @@ def maybe_droplevels(indexer, levels, drop_level):
 
                 result = loc if result is None else result & loc
 
-            return result, maybe_droplevels(result, level, drop_level)
+            return result, maybe_mi_droplevels(result, level, drop_level)
 
         level = self._get_level_number(level)
 
@@ -2793,7 +2791,7 @@ def maybe_droplevels(indexer, levels, drop_level):
             try:
                 if key in self.levels[0]:
                     indexer = self._get_level_indexer(key, level=level)
-                    new_index = maybe_droplevels(indexer, [0], drop_level)
+                    new_index = maybe_mi_droplevels(indexer, [0], drop_level)
                     return indexer, new_index
             except TypeError:
                 pass
@@ -2808,7 +2806,7 @@ def partial_selection(key, indexer=None):
                     ilevels = [
                         i for i in range(len(key)) if key[i] != slice(None, None)
                     ]
-                    return indexer, maybe_droplevels(indexer, ilevels, drop_level)
+                    return indexer, maybe_mi_droplevels(indexer, ilevels, drop_level)
 
                 if len(key) == self.nlevels and self.is_unique:
                     # Complete key in unique index -> standard get_loc
@@ -2843,10 +2841,10 @@ def partial_selection(key, indexer=None):
                 if indexer is None:
                     indexer = slice(None, None)
                 ilevels = [i for i in range(len(key)) if key[i] != slice(None, None)]
-                return indexer, maybe_droplevels(indexer, ilevels, drop_level)
+                return indexer, maybe_mi_droplevels(indexer, ilevels, drop_level)
         else:
             indexer = self._get_level_indexer(key, level=level)
-            return indexer, maybe_droplevels(indexer, [level], drop_level)
+            return indexer, maybe_mi_droplevels(indexer, [level], drop_level)
 
     def _get_level_indexer(self, key, level=0, indexer=None):
         # return an indexer, boolean array or a slice showing where the key is
@@ -3464,3 +3462,34 @@ def _sparsify(label_list, start=0, sentinel=""):
 
 def _get_na_rep(dtype):
     return {np.datetime64: "NaT", np.timedelta64: "NaT"}.get(dtype, "NaN")
+
+
+def maybe_droplevels(index, key):
+    """
+    Attempt to drop level or levels from the given index.
+
+    Parameters
+    ----------
+    index: Index
+    key : scalar or tuple
+
+    Returns
+    -------
+    Index
+    """
+    # drop levels
+    original_index = index
+    if isinstance(key, tuple):
+        for _ in key:
+            try:
+                index = index.droplevel(0)
+            except ValueError:
+                # we have dropped too much, so back out
+                return original_index
+    else:
+        try:
+            index = index.droplevel(0)
+        except ValueError:
+            pass
+
+    return index

pandas/core/indexing.py

@@ -226,7 +226,7 @@ def _validate_key(self, key, axis: int):
     def _has_valid_tuple(self, key: Tuple):
         """ check the key for valid keys across my indexer """
         for i, k in enumerate(key):
-            if i >= self.obj.ndim:
+            if i >= self.ndim:
                 raise IndexingError("Too many indexers")
             try:
                 self._validate_key(k, i)
@@ -254,7 +254,7 @@ def _convert_tuple(self, key, is_setter: bool = False):
                     keyidx.append(slice(None))
         else:
             for i, k in enumerate(key):
-                if i >= self.obj.ndim:
+                if i >= self.ndim:
                     raise IndexingError("Too many indexers")
                 idx = self._convert_to_indexer(k, axis=i, is_setter=is_setter)
                 keyidx.append(idx)
@@ -286,7 +286,7 @@ def _has_valid_positional_setitem_indexer(self, indexer):
             raise IndexError("{0} cannot enlarge its target object".format(self.name))
         else:
             if not isinstance(indexer, tuple):
-                indexer = self._tuplify(indexer)
+                indexer = _tuplify(self.ndim, indexer)
             for ax, i in zip(self.obj.axes, indexer):
                 if isinstance(i, slice):
                     # should check the stop slice?
@@ -401,7 +401,7 @@ def _setitem_with_indexer(self, indexer, value):
             assert info_axis == 1
 
             if not isinstance(indexer, tuple):
-                indexer = self._tuplify(indexer)
+                indexer = _tuplify(self.ndim, indexer)
 
             if isinstance(value, ABCSeries):
                 value = self._align_series(indexer, value)
@@ -670,7 +670,7 @@ def ravel(i):
             aligners = [not com.is_null_slice(idx) for idx in indexer]
             sum_aligners = sum(aligners)
             single_aligner = sum_aligners == 1
-            is_frame = self.obj.ndim == 2
+            is_frame = self.ndim == 2
             obj = self.obj
 
             # are we a single alignable value on a non-primary
@@ -731,7 +731,7 @@ def ravel(i):
         raise ValueError("Incompatible indexer with Series")
 
     def _align_frame(self, indexer, df: ABCDataFrame):
-        is_frame = self.obj.ndim == 2
+        is_frame = self.ndim == 2
 
         if isinstance(indexer, tuple):
 
@@ -867,7 +867,7 @@ def _handle_lowerdim_multi_index_axis0(self, tup: Tuple):
         except KeyError as ek:
             # raise KeyError if number of indexers match
             # else IndexingError will be raised
-            if len(tup) <= self.obj.index.nlevels and len(tup) > self.obj.ndim:
+            if len(tup) <= self.obj.index.nlevels and len(tup) > self.ndim:
                 raise ek
         except Exception as e1:
             if isinstance(tup[0], (slice, Index)):
@@ -900,7 +900,7 @@ def _getitem_lowerdim(self, tup: Tuple):
             if result is not None:
                 return result
 
-        if len(tup) > self.obj.ndim:
+        if len(tup) > self.ndim:
             raise IndexingError("Too many indexers. handle elsewhere")
 
         # to avoid wasted computation
@@ -1274,11 +1274,6 @@ def _convert_to_indexer(
                     return {"key": obj}
                 raise
 
-    def _tuplify(self, loc):
-        tup = [slice(None, None) for _ in range(self.ndim)]
-        tup[0] = loc
-        return tuple(tup)
-
     def _get_slice_axis(self, slice_obj: slice, axis: int):
         # caller is responsible for ensuring non-None axis
         obj = self.obj
@@ -2077,6 +2072,8 @@ def _getitem_tuple(self, tup: Tuple):
 
             # if the dim was reduced, then pass a lower-dim the next time
             if retval.ndim < self.ndim:
+                # TODO: this is never reached in tests; can we confirm that
+                #  it is impossible?
                 axis -= 1
 
             # try to get for the next axis
@@ -2152,7 +2149,7 @@ def _convert_to_indexer(
             )
 
 
-class _ScalarAccessIndexer(_NDFrameIndexer):
+class _ScalarAccessIndexer(_NDFrameIndexerBase):
     """ access scalars quickly """
 
     def _convert_key(self, key, is_setter: bool = False):
@@ -2178,8 +2175,8 @@ def __setitem__(self, key, value):
             key = com.apply_if_callable(key, self.obj)
 
         if not isinstance(key, tuple):
-            key = self._tuplify(key)
-        if len(key) != self.obj.ndim:
+            key = _tuplify(self.ndim, key)
+        if len(key) != self.ndim:
             raise ValueError("Not enough indexers for scalar access (setting)!")
         key = list(self._convert_key(key, is_setter=True))
         key.append(value)
@@ -2309,9 +2306,6 @@ class _iAtIndexer(_ScalarAccessIndexer):
 
     _takeable = True
 
-    def _has_valid_setitem_indexer(self, indexer):
-        self._has_valid_positional_setitem_indexer(indexer)
-
     def _convert_key(self, key, is_setter: bool = False):
         """ require integer args (and convert to label arguments) """
         for a, i in zip(self.obj.axes, key):
@@ -2320,6 +2314,25 @@ def _convert_key(self, key, is_setter: bool = False):
         return key
 
 
+def _tuplify(ndim: int, loc) -> tuple:
+    """
+    Given an indexer for the first dimension, create an equivalent tuple
+    for indexing over all dimensions.
+
+    Parameters
+    ----------
+    ndim : int
+    loc : object
+
+    Returns
+    -------
+    tuple
+    """
+    tup = [slice(None, None) for _ in range(ndim)]
+    tup[0] = loc
+    return tuple(tup)
+
+
 def convert_to_index_sliceable(obj, key):
     """
     if we are index sliceable, then return my slicer, otherwise return None
@@ -2469,25 +2482,6 @@ def need_slice(obj):
     )
 
 
-def maybe_droplevels(index, key):
-    # drop levels
-    original_index = index
-    if isinstance(key, tuple):
-        for _ in key:
-            try:
-                index = index.droplevel(0)
-            except ValueError:
-                # we have dropped too much, so back out
-                return original_index
-    else:
-        try:
-            index = index.droplevel(0)
-        except ValueError:
-            pass
-
-    return index
-
-
 def _non_reducing_slice(slice_):
     """
     Ensurse that a slice doesn't reduce to a Series or Scalar.