Raise a ValueError when index and data lengths don't match

doc/source/whatsnew/v0.25.0.rst

@@ -630,6 +630,7 @@ Indexing
 
 - Improved exception message when calling :meth:`DataFrame.iloc` with a list of non-numeric objects (:issue:`25753`).
 - Bug in :meth:`DataFrame.loc` and :meth:`Series.loc` where ``KeyError`` was not raised for a ``MultiIndex`` when the key was less than or equal to the number of levels in the :class:`MultiIndex` (:issue:`14885`).
+- Bug in ``.iloc`` and ``.loc`` where ``ValueError`` was not raised for a boolean index with different length  (:issue:`26658`).
 - Bug in which :meth:`DataFrame.append` produced an erroneous warning indicating that a ``KeyError`` will be thrown in the future when the data to be appended contains new columns (:issue:`22252`).
 - Bug in which :meth:`DataFrame.to_csv` caused a segfault for a reindexed data frame, when the indices were single-level :class:`MultiIndex` (:issue:`26303`).
 - Fixed bug where assigning a :class:`arrays.PandasArray` to a :class:`pandas.core.frame.DataFrame` would raise error (:issue:`26390`)

pandas/core/indexing.py

@@ -1441,6 +1441,9 @@ def _getbool_axis(self, key, axis=None):
             axis = self.axis or 0
         labels = self.obj._get_axis(axis)
         key = check_bool_indexer(labels, key)
+        if 0 < len(labels) != len(key):
+            raise ValueError('Item wrong length %d instead of %d.' %
+                             (len(key), len(labels)))
         inds, = key.nonzero()
         try:
             return self.obj._take(inds, axis=axis)

pandas/tests/indexing/test_iloc.py

@@ -265,6 +265,19 @@ def test_iloc_getitem_bool(self):
                           typs=['labels', 'mixed', 'ts', 'floats', 'empty'],
                           fails=IndexError)
 
+    def test_iloc_getitem_bool_diff_len(self):
+        # GH26658
+        too_short = [True, False]
+        too_long = [True, False, True, False, False]
+        self.check_result('bool', 'iloc', too_short, 'ix', too_short,
+                          typs=['ints', 'uints', 'labels',
+                                'mixed', 'ts', 'floats'],
+                          fails=ValueError)
+        self.check_result('bool', 'iloc', too_long, 'ix', too_long,
+                          typs=['ints', 'uints', 'labels',
+                                'mixed', 'ts', 'floats'],
+                          fails=ValueError)
+
     def test_iloc_getitem_slice(self):
 
         # slices

pandas/tests/indexing/test_loc.py

@@ -196,6 +196,19 @@ def test_loc_getitem_bool(self):
         self.check_result('bool', 'loc', b, 'ix', b, typs=['empty'],
                           fails=KeyError)
 
+    def test_loc_getitem_bool_diff_len(self):
+        # GH26658
+        too_short = [True, False]
+        too_long = [True, False, True, False, False]
+        self.check_result('bool', 'loc', too_short, 'ix', too_short,
+                          typs=['ints', 'uints', 'labels',
+                                'mixed', 'ts', 'floats'],
+                          fails=ValueError)
+        self.check_result('bool', 'loc', too_long, 'ix', too_long,
+                          typs=['ints', 'uints', 'labels',
+                                'mixed', 'ts', 'floats'],
+                          fails=ValueError)
+
     def test_loc_getitem_int_slice(self):
 
         # ok