BUG: use np.iterable to check for iterable, close #1773

pandas/core/frame.py

@@ -2610,16 +2610,15 @@ def duplicated(self, cols=None, take_last=False):
         -------
         duplicated : Series
         """
-        if cols is not None:
-            if isinstance(cols, list):
+        if cols is None:
+            values = list(self.values.T)
+        else:
+            if np.iterable(cols):
                 values = [self[x].values for x in cols]
-                keys = lib.fast_zip_fillna(values)
             else:
-                keys = lib.fast_zip_fillna([self[cols]])
-        else:
-            values = list(self.values.T)
-            keys = lib.fast_zip_fillna(values)
+                values = [self[cols]]
 
+        keys = lib.fast_zip_fillna(values)
         duplicated = lib.duplicated(keys, take_last=take_last)
         return Series(duplicated, index=self.index)
 

pandas/tests/test_frame.py

@@ -3885,11 +3885,13 @@ def test_drop_duplicates(self):
         assert_frame_equal(result, expected)
 
         # multi column
-        result = df.drop_duplicates(['A', 'B'])
         expected = df.ix[[0, 1, 2, 3]]
+        result = df.drop_duplicates(np.array(['A', 'B']))
+        assert_frame_equal(result, expected)
+        result = df.drop_duplicates(['A', 'B'])
         assert_frame_equal(result, expected)
 
-        result = df.drop_duplicates(['A', 'B'], take_last=True)
+        result = df.drop_duplicates(('A', 'B'), take_last=True)
         expected = df.ix[[0, 5, 6, 7]]
         assert_frame_equal(result, expected)