Not only is this a complex ePub, it is riddled with errors, for instance, in the download chapter, they left out the leading portion of the download URLs and epubcheck was very unhappy with the ePub.
i.e.
archives/python-3.12.1-docs.epub instead of
https://docs.python.org/3/archives/p...12.1-docs.epub.
For what it may be worth, calibre on my desktop converted the ePub to azw3 in about 9 minutes spending most of that time sitting at 67%.