Consistent Timedelta Writing for all Excel Engines (pandas-dev#19921)

Author: WillAyd

doc/source/whatsnew/v0.23.0.txt

@@ -867,7 +867,7 @@ I/O
 - Bug in :func:`read_json` where large numeric values were causing an ``OverflowError`` (:issue:`18842`)
 - Bug in :func:`DataFrame.to_parquet` where an exception was raised if the write destination is S3 (:issue:`19134`)
 - :class:`Interval` now supported in :func:`DataFrame.to_excel` for all Excel file types (:issue:`19242`)
-- :class:`Timedelta` now supported in :func:`DataFrame.to_excel` for xls file type (:issue:`19242`, :issue:`9155`)
+- :class:`Timedelta` now supported in :func:`DataFrame.to_excel` for all Excel file types (:issue:`19242`, :issue:`9155`, :issue:`19900`)
 - Bug in :meth:`pandas.io.stata.StataReader.value_labels` raising an ``AttributeError`` when called on very old files. Now returns an empty dict (:issue:`19417`)
 
 Plotting

pandas/io/excel.py

@@ -779,35 +779,6 @@ def _pop_header_name(row, index_col):
         return none_fill(row[i]), row[:i] + [''] + row[i + 1:]
 
 
-def _conv_value(val):
-    """ Convert numpy types to Python types for the Excel writers.
-
-        Parameters
-        ----------
-        val : object
-            Value to be written into cells
-
-        Returns
-        -------
-        If val is a numpy int, float, or bool, then the equivalent Python
-        types are returned. :obj:`datetime`, :obj:`date`, and :obj:`timedelta`
-        are passed and formatting must be handled in the writer. :obj:`str`
-        representation is returned for all other types.
-    """
-    if is_integer(val):
-        val = int(val)
-    elif is_float(val):
-        val = float(val)
-    elif is_bool(val):
-        val = bool(val)
-    elif isinstance(val, (datetime, date, timedelta)):
-        pass
-    else:
-        val = compat.to_str(val)
-
-    return val
-
-
 @add_metaclass(abc.ABCMeta)
 class ExcelWriter(object):
     """
@@ -953,6 +924,39 @@ def _get_sheet_name(self, sheet_name):
                              'cur_sheet property')
         return sheet_name
 
+    def _value_with_fmt(self, val):
+        """Convert numpy types to Python types for the Excel writers.
+
+        Parameters
+        ----------
+        val : object
+            Value to be written into cells
+
+        Returns
+        -------
+        Tuple with the first element being the converted value and the second
+            being an optional format
+        """
+        fmt = None
+
+        if is_integer(val):
+            val = int(val)
+        elif is_float(val):
+            val = float(val)
+        elif is_bool(val):
+            val = bool(val)
+        elif isinstance(val, datetime):
+            fmt = self.datetime_format
+        elif isinstance(val, date):
+            fmt = self.date_format
+        elif isinstance(val, timedelta):
+            val = val.total_seconds() / float(86400)
+            fmt = '0'
+        else:
+            val = compat.to_str(val)
+
+        return val, fmt
+
     @classmethod
     def check_extension(cls, ext):
         """checks that path's extension against the Writer's supported
@@ -1382,7 +1386,9 @@ def write_cells(self, cells, sheet_name=None, startrow=0, startcol=0,
                 row=startrow + cell.row + 1,
                 column=startcol + cell.col + 1
             )
-            xcell.value = _conv_value(cell.val)
+            xcell.value, fmt = self._value_with_fmt(cell.val)
+            if fmt:
+                xcell.number_format = fmt
 
             style_kwargs = {}
             if cell.style:
@@ -1469,25 +1475,16 @@ def write_cells(self, cells, sheet_name=None, startrow=0, startcol=0,
         style_dict = {}
 
         for cell in cells:
-            val = _conv_value(cell.val)
-
-            num_format_str = None
-            if isinstance(cell.val, datetime):
-                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)
+            val, fmt = self._value_with_fmt(cell.val)
 
             stylekey = json.dumps(cell.style)
-            if num_format_str:
-                stylekey += num_format_str
+            if fmt:
+                stylekey += fmt
 
             if stylekey in style_dict:
                 style = style_dict[stylekey]
             else:
-                style = self._convert_to_style(cell.style, num_format_str)
+                style = self._convert_to_style(cell.style, fmt)
                 style_dict[stylekey] = style
 
             if cell.mergestart is not None and cell.mergeend is not None:
@@ -1745,23 +1742,17 @@ def write_cells(self, cells, sheet_name=None, startrow=0, startcol=0,
             wks.freeze_panes(*(freeze_panes))
 
         for cell in cells:
-            val = _conv_value(cell.val)
-
-            num_format_str = None
-            if isinstance(cell.val, datetime):
-                num_format_str = self.datetime_format
-            elif isinstance(cell.val, date):
-                num_format_str = self.date_format
+            val, fmt = self._value_with_fmt(cell.val)
 
             stylekey = json.dumps(cell.style)
-            if num_format_str:
-                stylekey += num_format_str
+            if fmt:
+                stylekey += fmt
 
             if stylekey in style_dict:
                 style = style_dict[stylekey]
             else:
                 style = self.book.add_format(
-                    _XlsxStyler.convert(cell.style, num_format_str))
+                    _XlsxStyler.convert(cell.style, fmt))
                 style_dict[stylekey] = style
 
             if cell.mergestart is not None and cell.mergeend is not None:

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