openpyxl-formula-editing

name	openpyxl-formula-editing
description	Editing existing Excel files with openpyxl while preserving formatting and adding formulas.

Editing Excel Files with openpyxl (Preserve Formatting)

Load and Edit

from openpyxl import load_workbook

wb = load_workbook('file.xlsx')
ws = wb['SheetName']

# Write formula to a cell (preserves existing formatting)
ws['H12'] = '=SOME_FORMULA()'

# Iterate over a range
for row in range(12, 18):
    for col_letter in ['H', 'I', 'J', 'K', 'L']:
        ws[f'{col_letter}{row}'] = f'=FORMULA({col_letter}...)'

wb.save('file.xlsx')

Important Notes

• Assigning a value to a cell preserves its existing formatting (fill, font, borders)
• Formulas are stored as strings starting with '='
• Use recalc.py after saving to compute formula values
• Never open with data_only=True if you plan to save (destroys formulas)