BUG: Issue 9798 fixed

Author: lucas

doc/source/whatsnew/v0.16.1.txt

@@ -88,3 +88,5 @@ Bug Fixes
 - Bug in ``FloatArrayFormatter`` where decision boundary for displaying "small" floats in decimal format is off by one order of magnitude for a given display.precision (:issue:`9764`)
 
 - Fixed bug where ``DataFrame.plot()`` raised an error when both ``color`` and ``style`` keywords were passed and there was no color symbol in the style strings (:issue:`9671`)
+
+- Bug in ``read_csv()`` interprets ``index_col=True`` as ``1`` (:issue:`9798`)

pandas/io/parsers.py

@@ -905,7 +905,7 @@ def _make_index(self, data, alldata, columns, indexnamerow=False):
 
     def _get_simple_index(self, data, columns):
         def ix(col):
-            if not isinstance(col, compat.string_types):
+            if not (isinstance(col, compat.string_types) or col is True):
                 return col
             raise ValueError('Index %s invalid' % col)
         index = None

pandas/io/tests/test_parsers.py

@@ -520,6 +520,11 @@ def test_usecols_index_col_False(self):
         df = self.read_csv(StringIO(s_malformed), usecols=cols, index_col=False)
         tm.assert_frame_equal(expected, df)
 
+    def test_index_col_is_True(self):
+        # Issue 9798
+        self.assertRaises(ValueError, self.read_csv, StringIO(self.ts_data),
+                          index_col=True)
+
     def test_converter_index_col_bug(self):
         # 1835
         data = "A;B\n1;2\n3;4"