Revert new warnings

pandas/core/frame.py

@@ -3862,29 +3862,10 @@ def set_index(self, keys, drop=True, append=False, inplace=False,
         -------
         dataframe : DataFrame
         """
-        from pandas import Series
-
+        inplace = validate_bool_kwarg(inplace, 'inplace')
         if not isinstance(keys, list):
             keys = [keys]
 
-        # collect elements from "keys" that are not allowed array types
-        col_labels = [x for x in keys
-                      if not isinstance(x, (Series, Index, MultiIndex,
-                                            list, np.ndarray))]
-        if any(x not in self for x in col_labels):
-            # if there are any labels that are invalid, we raise a KeyError
-            missing = [x for x in col_labels if x not in self]
-            raise KeyError('{}'.format(missing))
-
-        elif len(set(col_labels)) < len(col_labels):
-            # if all are valid labels, but there are duplicates
-            dup = Series(col_labels)
-            dup = list(dup.loc[dup.duplicated()])
-            raise ValueError('Passed duplicate column names '
-                             'to keys: {dup}'.format(dup=dup))
-
-        inplace = validate_bool_kwarg(inplace, 'inplace')
-
         if inplace:
             frame = self
         else:

pandas/tests/frame/test_alter_axes.py

@@ -185,9 +185,8 @@ def test_set_index_pass_arrays_duplicate(self, frame_of_index_cols, drop,
         keys = [box1(df['A']), box2(df['A'])]
 
         # == gives ambiguous Boolean for Series
-        if keys[0] is 'A' and keys[1] is 'A':
-            with tm.assert_raises_regex(ValueError,
-                                        'Passed duplicate column names.*'):
+        if drop and keys[0] is 'A' and keys[1] is 'A':
+            with tm.assert_raises_regex(KeyError, '.*'):
                 df.set_index(keys, drop=drop, append=append)
         else:
             result = df.set_index(keys, drop=drop, append=append)
@@ -225,15 +224,17 @@ def test_set_index_verify_integrity(self, frame_of_index_cols):
                                     'Index has duplicate keys'):
             df.set_index([df['A'], df['A']], verify_integrity=True)
 
-    def test_set_index_raise(self, frame_of_index_cols):
+    @pytest.mark.parametrize('append', [True, False])
+    @pytest.mark.parametrize('drop', [True, False])
+    def test_set_index_raise(self, frame_of_index_cols, drop, append):
         df = frame_of_index_cols
 
         with tm.assert_raises_regex(KeyError, '.*'):  # column names are A-E
-            df.set_index(['foo', 'bar', 'baz'], verify_integrity=True)
+            df.set_index(['foo', 'bar', 'baz'], drop=drop, append=append)
 
         # non-existent key in list with arrays
         with tm.assert_raises_regex(KeyError, '.*'):
-            df.set_index([df['A'], df['B'], 'X'], verify_integrity=True)
+            df.set_index([df['A'], df['B'], 'X'], drop=drop, append=append)
 
     def test_construction_with_categorical_index(self):
         ci = tm.makeCategoricalIndex(10)