BUG: Do not allow boolean values for indexing with .loc without a boolean index.

pandas/core/dtypes/common.py

@@ -1386,7 +1386,7 @@ def is_bool_dtype(arr_or_dtype) -> bool:
         # we don't have a boolean Index class
         # so its object, we need to infer to
         # guess this
-        return arr_or_dtype.is_object and arr_or_dtype.inferred_type == "boolean"
+        return arr_or_dtype.is_object() and arr_or_dtype.inferred_type == "boolean"
     elif is_extension_array_dtype(arr_or_dtype):
         return getattr(dtype, "_is_boolean", False)
 

pandas/core/indexing.py

@@ -961,12 +961,17 @@ class _LocIndexer(_LocationIndexer):
 
     @doc(_LocationIndexer._validate_key)
     def _validate_key(self, key, axis: int):
-
         # valid for a collection of labels (we check their presence later)
         # slice of labels (where start-end in labels)
         # slice of integers (only if in the labels)
-        # boolean
-        pass
+        # boolean not in slice and with boolean index
+        if not is_bool_dtype(self.obj.index) and isinstance(key, bool):
+            raise TypeError("Boolean label can not be used without a boolean index")
+
+        if isinstance(key, slice) and (
+            isinstance(key.start, bool) or isinstance(key.stop, bool)
+        ):
+            raise TypeError("Boolean values can not be used in a slice")
 
     def _has_valid_setitem_indexer(self, indexer) -> bool:
         return True
@@ -2366,7 +2371,7 @@ def convert_missing_indexer(indexer):
         indexer = indexer["key"]
 
         if isinstance(indexer, bool):
-            raise KeyError("cannot use a single bool to index into setitem")
+            raise TypeError("cannot use a single bool to index into setitem")
         return indexer, True
 
     return indexer, False

pandas/tests/frame/indexing/test_indexing.py

@@ -947,16 +947,16 @@ def test_getitem_ix_boolean_duplicates_multiple(self):
     def test_getitem_setitem_ix_bool_keyerror(self):
         # #2199
         df = DataFrame({"a": [1, 2, 3]})
-
-        with pytest.raises(KeyError, match=r"^False$"):
+        message = "Boolean label can not be used without a boolean index"
+        with pytest.raises(TypeError, match=message):
             df.loc[False]
-        with pytest.raises(KeyError, match=r"^True$"):
+        with pytest.raises(TypeError, match=message):
             df.loc[True]
 
         msg = "cannot use a single bool to index into setitem"
-        with pytest.raises(KeyError, match=msg):
+        with pytest.raises(TypeError, match=msg):
             df.loc[False] = 0
-        with pytest.raises(KeyError, match=msg):
+        with pytest.raises(TypeError, match=msg):
             df.loc[True] = 0
 
     # TODO: rename?  remove?

pandas/tests/indexing/test_loc.py

@@ -23,12 +23,15 @@
     DatetimeIndex,
     Index,
     IndexSlice,
+    Int64Index,
     MultiIndex,
     Period,
+    RangeIndex,
     Series,
     SparseDtype,
     Timedelta,
     Timestamp,
+    UInt64Index,
     date_range,
     timedelta_range,
     to_datetime,
@@ -2085,6 +2088,60 @@ def test_loc_getitem_slice_columns_mixed_dtype(self):
         tm.assert_frame_equal(df.loc[:, 1:], expected)
 
 
+class TestLocBooleanLabelsAndSlices(Base):
+    @pytest.mark.parametrize(
+        "index",
+        [
+            RangeIndex(4),
+            Int64Index(range(4)),
+            UInt64Index(range(4)),
+            pd.Float64Index(range(4)),
+            CategoricalIndex(range(4)),
+            date_range(0, periods=4, freq="ns"),
+            timedelta_range(0, periods=4, freq="ns"),
+            pd.interval_range(0, periods=4),
+            Index([0, 1, 2, 3], dtype=object),
+            MultiIndex.from_product([[0, 1], [0, 1]]),
+            pd.period_range("2018Q1", freq="Q", periods=4),
+        ],
+    )
+    def test_loc_bool_incompatible_index_raises(self, index, frame_or_series):
+        # GH20432
+        message = "Boolean label can not be used without a boolean index"
+        obj = frame_or_series(range(4), index=index)
+        with pytest.raises(TypeError, match=message):
+            obj.loc[True]
+
+    @pytest.mark.parametrize("index", [Index([True, False], dtype="boolean")])
+    def test_loc_bool_should_not_raise(self, index, frame_or_series):
+        obj = frame_or_series(range(2), index=index)
+        obj.loc[True]
+
+    @pytest.mark.parametrize(
+        "index",
+        [
+            RangeIndex(4),
+            Int64Index(range(4)),
+            UInt64Index(range(4)),
+            pd.Float64Index(range(4)),
+            CategoricalIndex(range(4)),
+            date_range(0, periods=4, freq="ns"),
+            timedelta_range(0, periods=4, freq="ns"),
+            pd.interval_range(0, periods=4),
+            Index([0, 1, 2, 3], dtype=object),
+            Index([True, True, False, False], dtype=object),
+            MultiIndex.from_product([[0, 1], [0, 1]]),
+            pd.period_range("2018Q1", freq="Q", periods=4),
+        ],
+    )
+    def test_loc_bool_slice_raises(self, index, frame_or_series):
+        # GH20432
+        message = "Boolean values can not be used in a slice"
+        obj = frame_or_series(range(4), index=index)
+        with pytest.raises(TypeError, match=message):
+            obj.loc[True:False]
+
+
 class TestLocBooleanMask:
     def test_loc_setitem_bool_mask_timedeltaindex(self):
         # GH#14946