Consistent timedelta writing for all Excel engines

Author: WillAyd

pandas/io/excel.py

@@ -1380,6 +1380,12 @@ def write_cells(self, cells, sheet_name=None, startrow=0, startcol=0,
             )
             xcell.value = _conv_value(cell.val)
 
+            if isinstance(cell.val, timedelta):
+                delta = cell.val
+                xcell.value = delta.total_seconds() / float(86400)
+                # Set format to prevent conversion to datetime
+                xcell.number_format = '0'
+
             style_kwargs = {}
             if cell.style:
                 key = str(cell.style)
@@ -1748,6 +1754,9 @@ def write_cells(self, cells, sheet_name=None, startrow=0, startcol=0,
                 num_format_str = self.datetime_format
             elif isinstance(cell.val, date):
                 num_format_str = self.date_format
+            elif isinstance(cell.val, timedelta):
+                delta = cell.val
+                val = delta.total_seconds() / float(86400)
 
             stylekey = json.dumps(cell.style)
             if num_format_str:

pandas/tests/io/test_excel.py

@@ -1373,11 +1373,6 @@ def test_to_excel_interval_labels(self, merge_cells, engine, ext):
 
     def test_to_excel_timedelta(self, merge_cells, engine, ext):
         # GH 19242, GH9155 - test writing timedelta to xls
-        if engine == 'openpyxl':
-            pytest.xfail('Timedelta roundtrip broken with openpyxl')
-        if engine == 'xlsxwriter' and (sys.version_info[0] == 2 and
-                                       sys.platform.startswith('linux')):
-            pytest.xfail('Not working on linux with Py2 and xlsxwriter')
         frame = DataFrame(np.random.randint(-10, 10, size=(20, 1)),
                           columns=['A'],
                           dtype=np.int64