Fix passing empty label to df drop

pandas/core/generic.py

@@ -3138,12 +3138,7 @@ def _drop_axis(self, labels, axis, level=None, errors='raise'):
                 new_axis = axis.drop(labels, level=level, errors=errors)
             else:
                 new_axis = axis.drop(labels, errors=errors)
-            dropped = self.reindex(**{axis_name: new_axis})
-            try:
-                dropped.axes[axis_].set_names(axis.names, inplace=True)
-            except AttributeError:
-                pass
-            result = dropped
+            result = self.reindex(**{axis_name: new_axis})
 
         else:
             labels = _ensure_object(com._index_labels_to_array(labels))
@@ -3154,8 +3149,12 @@ def _drop_axis(self, labels, axis, level=None, errors='raise'):
             else:
                 indexer = ~axis.isin(labels)
 
-            if errors == 'raise' and indexer.all():
-                raise KeyError('{} not found in axis'.format(labels))
+            # Check if label doesn't exist along axis
+            if len(labels):
+                labels_missing = (~np.array([label in axis
+                                             for label in labels])).any()
+                if errors == 'raise' and labels_missing:
+                    raise KeyError('{} not found in axis'.format(labels))
 
             slicer = [slice(None)] * self.ndim
             slicer[self._get_axis_number(axis_name)] = indexer

pandas/core/indexes/base.py

@@ -4335,13 +4335,13 @@ def drop(self, labels, errors='raise'):
         Raises
         ------
         KeyError
-            If none of the labels are found in the selected axis
+            If not all of the labels are found in the selected axis
         """
         arr_dtype = 'object' if self.dtype == 'object' else None
         labels = com._index_labels_to_array(labels, dtype=arr_dtype)
         indexer = self.get_indexer(labels)
         mask = indexer == -1
-        if mask.any():
+        if mask.any() and len(mask):
             if errors != 'ignore':
                 raise KeyError(
                     'labels %s not contained in axis' % labels[mask])

pandas/core/indexes/multi.py

@@ -1719,7 +1719,6 @@ def drop(self, labels, level=None, errors='raise'):
                 if errors != 'ignore':
                     raise ValueError('labels %s not contained in axis' %
                                      labels[mask])
-                indexer = indexer[~mask]
         except Exception:
             pass
 

pandas/tests/series/indexing/test_alter_index.py

@@ -514,3 +514,25 @@ def test_drop():
     s = Series([2, 3], index=[0, 1])
     with tm.assert_raises_regex(KeyError, 'not contained in axis'):
         s.drop([False, True])
+
+
+@pytest.mark.parametrize('index, drop_labels, expected_index', [
+    ([1, 2, 3], [], [1, 2, 3]),
+    ([1, 1, 2], [], [1, 1, 2]),
+    ([1, 2, 3], [2], [1, 3]),
+    ([1, 1, 3], [1], [3]),
+])
+def test_drop_empty_list(index, drop_labels, expected_index):
+    # GH 21494
+    df = pd.DataFrame(index=index).drop(drop_labels)
+    assert (df.index.values == expected_index).all()
+
+
+@pytest.mark.parametrize('index, drop_labels, error_key', [
+    ([1, 2, 3], [1, 4], 'not contained in axis'),
+    ([1, 2, 2], [1, 4], 'not found in axis'),
+])
+def test_drop_non_empty_list(index, drop_labels, error_key):
+    # GH 21494
+    with tm.assert_raises_regex(KeyError, error_key):
+        pd.DataFrame(index=index).drop(drop_labels)