[lxml] %s formatting in documentation (in stead of f-string)

Switching to lxml for xml parsing and generating, I was somewhat puzzeled by the usage line's like XHTML_NAMESPACE = "http://www.w3.org/1999/xhtml" XHTML = "{%s}" % XHTML_NAMESPACE With more modern f-string's this could also be written as XHTML = f"{{{XHTML_NAMESPACE}}}" This may be because I only started on Python on 3.7, and have never worked with any 2.x I quite understand there is no time to rework all the doc's in the low income on this project. Just two questions: - is there (another) good reason not to is f-string formatting? And if not - is there a way to assist on reworking the doc's Thomas Roes