Add round trip test

Added round trip test and fixed error in writing sheets when
merge_cells=false and columns have multi index

Author: Dr-Irv

pandas/core/format.py

@@ -1867,8 +1867,8 @@ def _format_hierarchical_rows(self):
 
             # MultiIndex columns require an extra row
             # with index names (blank if None) for
-            # unambigous round-trip
-            if isinstance(self.columns, MultiIndex):
+            # unambigous round-trip, but only if merged
+            if isinstance(self.columns, MultiIndex) and not self.merge_cells:
                 self.rowcounter += 1
 
             # if index labels are not empty go ahead and dump

pandas/io/parsers.py

@@ -866,19 +866,19 @@ def _extract_multi_indexer_columns(self, header, index_names, col_names,
         # extract the columns
         field_count = len(header[0])
 
-        def tostr(x):
-            return str(x) if not isinstance(x, compat.string_types) else x
-
         def extract(r):
-            return tuple([tostr(r[i]) for i in range(field_count) if i not in sic])
+            return tuple([r[i] for i in range(field_count) if i not in sic])
 
         columns = lzip(*[extract(r) for r in header])
         names = ic + columns
 
+        def tostr(x):
+            return str(x) if not isinstance(x, compat.string_types) else x
+
         # if we find 'Unnamed' all of a single level, then our header was too
         # long
         for n in range(len(columns[0])):
-            if all(['Unnamed' in c[n] for c in columns]):
+            if all(['Unnamed' in tostr(c[n]) for c in columns]):
                 raise _parser.CParserError(
                     "Passed header=[%s] are too many rows for this "
                     "multi_index of columns"

pandas/io/tests/test_excel.py

@@ -558,7 +558,7 @@ def test_read_excel_multiindex(self):
         tm.assert_frame_equal(actual, expected)
 
         # Issue #11317
-        expected.columns = mi.set_levels(['1','2'],level=1).set_names(['c1', 'c2'])
+        expected.columns = mi.set_levels([1,2],level=1).set_names(['c1', 'c2'])
         actual = read_excel(mi_file, 'name_with_int', index_col=0, header=[0,1])
         tm.assert_frame_equal(actual, expected)
 
@@ -1074,6 +1074,31 @@ def test_to_excel_multiindex(self):
                               parse_dates=False)
             tm.assert_frame_equal(frame, df)
             self.assertEqual(frame.index.names, df.index.names)
+            
+    def test_to_excel_multiindex_cols(self):
+        _skip_if_no_xlrd()
+        if not self.merge_cells:
+            raise nose.SkipTest('Skip tests MI on cols with no merging.')
+
+
+        frame = self.frame
+        arrays = np.arange(len(frame.index) * 2).reshape(2, -1)
+        new_index = MultiIndex.from_arrays(arrays,
+                                           names=['first', 'second'])
+        frame.index = new_index
+
+        new_cols_index = MultiIndex.from_tuples([(40,1),(40,2),(50,1),(50,2)])
+        frame.columns = new_cols_index
+
+        with ensure_clean(self.ext) as path:
+             # round trip
+            frame.to_excel(path, 'test1', merge_cells=self.merge_cells)
+            reader = ExcelFile(path)
+            df = read_excel(reader, 'test1', header=[0,1],
+                             index_col=[0, 1],
+                              parse_dates=False)
+            tm.assert_frame_equal(frame, df)
+            self.assertEqual(frame.index.names, df.index.names)
 
     def test_to_excel_multiindex_dates(self):
         _skip_if_no_xlrd()