STYLE: Fix whitespace in ExcelFormatter and TestExcelWriter for consistency

Author: Justine Kosinski

pandas/io/formats/excel.py

@@ -654,7 +654,7 @@ def _format_header_mi(self) -> Iterable[ExcelCell]:
             # Get values from original columns (which have NaN), not fixed_columns
             orig_level_values = columns.get_level_values(lnum)
             # Extract the values according to the order in fixed_columns
-            values = orig_level_values[:len(level_codes)]
+            values = orig_level_values[: len(level_codes)]
             for i, span_val in spans.items():
                 mergestart, mergeend = None, None
                 if merge_columns and span_val > 1:

pandas/tests/io/excel/test_writers.py

@@ -1525,13 +1525,13 @@ def test_to_excel_multiindex_nan_in_columns(self, merge_cells, tmp_excel):
 
         with ExcelFile(tmp_excel) as reader:
             result = pd.read_excel(reader, index_col=0, header=[0, 1])
-        
+
         # Test structure is preserved
         assert result.shape == df.shape
         assert list(result.index) == list(df.index)
         assert isinstance(result.columns, MultiIndex)
         assert result.columns.nlevels == df.columns.nlevels
-        
+
         # Test data values are preserved (most important part)
         tm.assert_numpy_array_equal(result.to_numpy(), df.to_numpy())