Yes, 2.7 is also affected at https://github.com/python/cpython/blob/befe3f7afdc5279b320af88a9e57f682c0172599/Lib/difflib.py#L2001 . I think it was missed during the initial addition in issue914575 and no one would be using it as a feature to have custom HTML directly injected in table header using fromdesc and todesc. So I hope this won't be breaking anyone on 2.7 and even with that headers can still be customized with CSS. Also as an additional note HtmlDiff.make_file internally uses make_table to construct full HTML file and that is also fixed. Maybe if one of the original authors of difflib would like to confirm it then it would be great.