Fixes to document issue in code, small efficiency fix

Author: Dr-Irv

pandas/core/format.py

@@ -1874,7 +1874,7 @@ def _format_hierarchical_rows(self):
             # MultiIndex columns require an extra row
             # with index names (blank if None) for
             # unambigous round-trip, unless not merging,
-            # in which case the names all go on one row
+            # in which case the names all go on one row Issue #11328
             if isinstance(self.columns, MultiIndex) and self.merge_cells:
                 self.rowcounter += 1
 

pandas/io/excel.py

@@ -708,9 +708,9 @@ def write_cells(self, cells, sheet_name=None, startrow=0, startcol=0):
         for cell in cells:
             colletter = get_column_letter(startcol + cell.col + 1)
             xcell = wks.cell("%s%s" % (colletter, startrow + cell.row + 1))
-            new_data_type = xcell.data_type_for_value(cell.val)
             if (isinstance(cell.val, compat.string_types)
-                    and new_data_type != xcell.TYPE_STRING):
+                    and xcell.data_type_for_value(cell.val)
+                         != xcell.TYPE_STRING):
                 xcell.set_value_explicit(cell.val)
             else:
                 xcell.value = _conv_value(cell.val)

pandas/io/tests/test_excel.py

@@ -1089,7 +1089,10 @@ def test_to_excel_multiindex(self):
             df = read_excel(reader, 'test1', index_col=[0, 1],
                               parse_dates=False)
             tm.assert_frame_equal(frame, df)
-            
+
+    # Test for Issue 11328. If column indices are integers, make
+    # sure they are handled correctly for either setting of
+    # merge_cells
     def test_to_excel_multiindex_cols(self):
         _skip_if_no_xlrd()