From ebd9d031d5146ef722ffe3db301c1320ef86c9fe Mon Sep 17 00:00:00 2001
From: jbrockmendel <jbrockmendel@gmail.com>
Date: Wed, 24 Jul 2019 10:25:19 -0700
Subject: [PATCH 01/11] disable unused getitem

---
 pandas/core/generic.py                 | 2 +-
 pandas/tests/indexing/test_indexing.py | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index 9053edf2d1424..37f2399b38a89 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -3251,7 +3251,7 @@ def get(self, key, default=None):
             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."""
diff --git a/pandas/tests/indexing/test_indexing.py b/pandas/tests/indexing/test_indexing.py
index 8d1971801cccc..e375bd459e66f 100644
--- a/pandas/tests/indexing/test_indexing.py
+++ b/pandas/tests/indexing/test_indexing.py
@@ -8,6 +8,7 @@
 import pytest
 
 from pandas.compat import PY36
+from pandas.errors import AbstractMethodError
 
 from pandas.core.dtypes.common import is_float_dtype, is_integer_dtype
 
@@ -1168,7 +1169,7 @@ def test_extension_array_cross_section_converts():
 @pytest.mark.parametrize(
     "idxr, error, error_message",
     [
-        (lambda x: x, AttributeError, "'numpy.ndarray' object has no attribute 'get'"),
+        (lambda x: x, AbstractMethodError, None),
         (
             lambda x: x.loc,
             AttributeError,

From e0e039fddf7da4917c989c01f7d3173d48f793e6 Mon Sep 17 00:00:00 2001
From: jbrockmendel <jbrockmendel@gmail.com>
Date: Wed, 24 Jul 2019 10:28:41 -0700
Subject: [PATCH 02/11] remove unhit branch

---
 pandas/core/generic.py | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index 37f2399b38a89..2644d52354ee3 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -3346,11 +3346,8 @@ 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()
 
     def _slice(self, slobj, axis=0, kind=None):
         """

From 330f8af33b792fc9d444ff3e545745f8235f758d Mon Sep 17 00:00:00 2001
From: jbrockmendel <jbrockmendel@gmail.com>
Date: Wed, 24 Jul 2019 11:28:06 -0700
Subject: [PATCH 03/11] move maybe_droplevels

---
 pandas/core/frame.py         | 10 +++-------
 pandas/core/indexes/multi.py | 37 ++++++++++++++++++++++++++----------
 pandas/core/indexing.py      | 19 ------------------
 3 files changed, 30 insertions(+), 36 deletions(-)

diff --git a/pandas/core/frame.py b/pandas/core/frame.py
index 9a84f1ddd87a5..a9dcbe38ccaf1 100644
--- a/pandas/core/frame.py
+++ b/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,
@@ -2868,8 +2865,6 @@ 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
@@ -2980,6 +2975,7 @@ 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]
diff --git a/pandas/core/indexes/multi.py b/pandas/core/indexes/multi.py
index 0123230bc0f63..0e8e54444d51d 100644
--- a/pandas/core/indexes/multi.py
+++ b/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 +3462,22 @@ 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):
+    # 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
diff --git a/pandas/core/indexing.py b/pandas/core/indexing.py
index 1d4ea54ef0d70..239feed9a31a9 100755
--- a/pandas/core/indexing.py
+++ b/pandas/core/indexing.py
@@ -2469,25 +2469,6 @@ 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.

From ca16db20b581493ab995367e741aa3cb0e7ec1f4 Mon Sep 17 00:00:00 2001
From: jbrockmendel <jbrockmendel@gmail.com>
Date: Wed, 24 Jul 2019 11:41:45 -0700
Subject: [PATCH 04/11] make tuplify non-method

---
 pandas/core/indexing.py | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/pandas/core/indexing.py b/pandas/core/indexing.py
index 239feed9a31a9..34b269f9b9532 100755
--- a/pandas/core/indexing.py
+++ b/pandas/core/indexing.py
@@ -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)
@@ -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
@@ -2152,6 +2147,8 @@ def _convert_to_indexer(
             )
 
 
+# Note: aside from the constructor, this and subclasses do not use any
+#  _NDFrameIndexer methods
 class _ScalarAccessIndexer(_NDFrameIndexer):
     """ access scalars quickly """
 
@@ -2178,7 +2175,7 @@ def __setitem__(self, key, value):
             key = com.apply_if_callable(key, self.obj)
 
         if not isinstance(key, tuple):
-            key = self._tuplify(key)
+            key = _tuplify(self.ndim, key)
         if len(key) != self.obj.ndim:
             raise ValueError("Not enough indexers for scalar access (setting)!")
         key = list(self._convert_key(key, is_setter=True))
@@ -2320,6 +2317,12 @@ def _convert_key(self, key, is_setter: bool = False):
         return key
 
 
+def _tuplify(ndim: int, loc) -> 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

From 9dafe6040450aacedf42ca54f6f079b5642d1abc Mon Sep 17 00:00:00 2001
From: jbrockmendel <jbrockmendel@gmail.com>
Date: Wed, 24 Jul 2019 12:30:05 -0700
Subject: [PATCH 05/11] remove _has_valid_setitem_indexer

---
 pandas/core/indexing.py | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/pandas/core/indexing.py b/pandas/core/indexing.py
index 34b269f9b9532..a45bb780b765b 100755
--- a/pandas/core/indexing.py
+++ b/pandas/core/indexing.py
@@ -2147,9 +2147,7 @@ def _convert_to_indexer(
             )
 
 
-# Note: aside from the constructor, this and subclasses do not use any
-#  _NDFrameIndexer methods
-class _ScalarAccessIndexer(_NDFrameIndexer):
+class _ScalarAccessIndexer(_NDFrameIndexerBase):
     """ access scalars quickly """
 
     def _convert_key(self, key, is_setter: bool = False):
@@ -2306,9 +2304,6 @@ 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):

From f21e7d54e982ef675703817a0c2393f5ab65fc0e Mon Sep 17 00:00:00 2001
From: jbrockmendel <jbrockmendel@gmail.com>
Date: Wed, 24 Jul 2019 12:46:27 -0700
Subject: [PATCH 06/11] self.obj.ndim->self.ndim

---
 pandas/core/indexing.py | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/pandas/core/indexing.py b/pandas/core/indexing.py
index a45bb780b765b..30aac3259c5ca 100755
--- a/pandas/core/indexing.py
+++ b/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)
@@ -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
@@ -2174,7 +2174,7 @@ def __setitem__(self, key, value):
 
         if not isinstance(key, tuple):
             key = _tuplify(self.ndim, key)
-        if len(key) != self.obj.ndim:
+        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)

From dd5fc2d79a7c5c12c867503bcc4afffc316ea8a6 Mon Sep 17 00:00:00 2001
From: jbrockmendel <jbrockmendel@gmail.com>
Date: Wed, 24 Jul 2019 14:39:01 -0700
Subject: [PATCH 07/11] Comment

---
 pandas/core/indexing.py | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/pandas/core/indexing.py b/pandas/core/indexing.py
index 30aac3259c5ca..d648ae711c7cb 100755
--- a/pandas/core/indexing.py
+++ b/pandas/core/indexing.py
@@ -2072,6 +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

From 59e393568edd56f573f5efd368e085c50b5308f5 Mon Sep 17 00:00:00 2001
From: jbrockmendel <jbrockmendel@gmail.com>
Date: Wed, 24 Jul 2019 14:49:21 -0700
Subject: [PATCH 08/11] remove case handled by set_engine above

---
 pandas/core/series.py | 15 ---------------
 1 file changed, 15 deletions(-)

diff --git a/pandas/core/series.py b/pandas/core/series.py
index 418b3fc8c57d0..2cebbf103d8fb 100644
--- a/pandas/core/series.py
+++ b/pandas/core/series.py
@@ -47,7 +47,6 @@
     ABCSparseSeries,
 )
 from pandas.core.dtypes.missing import (
-    is_valid_nat_for_dtype,
     isna,
     na_value_for_dtype,
     notna,
@@ -1196,20 +1195,6 @@ def setitem(key, value):
                 elif key is Ellipsis:
                     self[:] = value
                     return
-                elif com.is_bool_indexer(key):
-                    pass
-                elif is_timedelta64_dtype(self.dtype):
-                    # reassign a null value to iNaT
-                    if is_valid_nat_for_dtype(value, self.dtype):
-                        # exclude np.datetime64("NaT")
-                        value = iNaT
-
-                        try:
-                            self.index._engine.set_value(self._values, key, value)
-                            return
-                        except (TypeError, ValueError):
-                            # ValueError appears in only some builds in CI
-                            pass
 
                 self.loc[key] = value
                 return

From e165ecaa01b7f78535951fa1966a694cb89096ab Mon Sep 17 00:00:00 2001
From: jbrockmendel <jbrockmendel@gmail.com>
Date: Wed, 24 Jul 2019 15:58:03 -0700
Subject: [PATCH 09/11] remove unused import

---
 pandas/core/series.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pandas/core/series.py b/pandas/core/series.py
index 2cebbf103d8fb..848e64eaf3cc6 100644
--- a/pandas/core/series.py
+++ b/pandas/core/series.py
@@ -12,7 +12,7 @@
 
 from pandas._config import get_option
 
-from pandas._libs import iNaT, index as libindex, lib, reshape, tslibs
+from pandas._libs import index as libindex, lib, reshape, tslibs
 from pandas.compat import PY36
 from pandas.compat.numpy import function as nv
 from pandas.util._decorators import Appender, Substitution, deprecate

From 5c4927e386a81dfbda1d1574d8828ead9bf37c2e Mon Sep 17 00:00:00 2001
From: jbrockmendel <jbrockmendel@gmail.com>
Date: Thu, 25 Jul 2019 10:57:27 -0700
Subject: [PATCH 10/11] docstrings

---
 pandas/core/indexes/multi.py | 12 ++++++++++++
 pandas/core/indexing.py      | 13 +++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/pandas/core/indexes/multi.py b/pandas/core/indexes/multi.py
index 0e8e54444d51d..a7c3449615299 100644
--- a/pandas/core/indexes/multi.py
+++ b/pandas/core/indexes/multi.py
@@ -3465,6 +3465,18 @@ def _get_na_rep(dtype):
 
 
 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):
diff --git a/pandas/core/indexing.py b/pandas/core/indexing.py
index d648ae711c7cb..cb33044c4e23f 100755
--- a/pandas/core/indexing.py
+++ b/pandas/core/indexing.py
@@ -2315,6 +2315,19 @@ def _convert_key(self, key, is_setter: bool = False):
 
 
 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)

From f0559a17010318cbd1da18fce62cb78994663a9e Mon Sep 17 00:00:00 2001
From: jbrockmendel <jbrockmendel@gmail.com>
Date: Thu, 25 Jul 2019 12:42:29 -0700
Subject: [PATCH 11/11] dummy commit to force ci