Alter the style of all cells with openpyxl

Updated: The comments show DEFAULT_FONT class can now be imported and the properties set directly before saving workbook:

from openpyxl.workbook import Workbook
from openpyxl.styles import DEFAULT_FONT
wb = Workbook()
wb.active['B3'] = "Hello"
DEFAULT_FONT.name = "Arial"
wb.save("DemoDefaultFont.xlsx")

More is needed to set multiple properties simultaneously. Copy the properties from a temporary Font object:

from openpyxl.workbook import Workbook
from openpyxl.styles import DEFAULT_FONT
from openpyxl.styles import Font
wb = Workbook()
wb.active['B3'] = "Hello"
_font = Font(name="Arial", sz=10, b=True)
{k: setattr(DEFAULT_FONT, k, v) for k, v in _font.__dict__.items()}
wb.save("DemoDefaultFont.xlsx")

Further details: https://openpyxl.readthedocs.io/en/stable/_modules/openpyxl/styles/fonts.html?highlight=default_font

There is no method to do this. At the moment the best approach would probably be to set the style for all the relevant columns or rows

style = Style(…)
for col in 'ABCD':
     ws._styles['A'] = style

I think we'll be working on improving handling styles in coming releases.