download your copy of epub/mobi of caltech fenman lecture on physics vol i http://www.feynmanlectures.caltech.edu/I_toc.html, powered by https://github.com/lepture/getbook/

feynman-lecture-vol-i.json

{
  "uid": "feynman-lecture-vol-i",
  "title": "The Feynman Lectures on Physics, Volume I",
  "author": "Richard Feynman",
  "chapters": ["http://www.feynmanlectures.caltech.edu/I_89.html","http://www.feynmanlectures.caltech.edu/I_90.html","http://www.feynmanlectures.caltech.edu/I_91.html","http://www.feynmanlectures.caltech.edu/I_92.html","http://www.feynmanlectures.caltech.edu/I_01.html","http://www.feynmanlectures.caltech.edu/I_02.html","http://www.feynmanlectures.caltech.edu/I_03.html","http://www.feynmanlectures.caltech.edu/I_04.html","http://www.feynmanlectures.caltech.edu/I_05.html","http://www.feynmanlectures.caltech.edu/I_06.html","http://www.feynmanlectures.caltech.edu/I_07.html","http://www.feynmanlectures.caltech.edu/I_08.html","http://www.feynmanlectures.caltech.edu/I_09.html","http://www.feynmanlectures.caltech.edu/I_10.html","http://www.feynmanlectures.caltech.edu/I_11.html","http://www.feynmanlectures.caltech.edu/I_12.html","http://www.feynmanlectures.caltech.edu/I_13.html","http://www.feynmanlectures.caltech.edu/I_14.html","http://www.feynmanlectures.caltech.edu/I_15.html","http://www.feynmanlectures.caltech.edu/I_16.html","http://www.feynmanlectures.caltech.edu/I_17.html","http://www.feynmanlectures.caltech.edu/I_18.html","http://www.feynmanlectures.caltech.edu/I_19.html","http://www.feynmanlectures.caltech.edu/I_20.html","http://www.feynmanlectures.caltech.edu/I_21.html","http://www.feynmanlectures.caltech.edu/I_22.html","http://www.feynmanlectures.caltech.edu/I_23.html","http://www.feynmanlectures.caltech.edu/I_24.html","http://www.feynmanlectures.caltech.edu/I_25.html","http://www.feynmanlectures.caltech.edu/I_26.html","http://www.feynmanlectures.caltech.edu/I_27.html","http://www.feynmanlectures.caltech.edu/I_28.html","http://www.feynmanlectures.caltech.edu/I_29.html","http://www.feynmanlectures.caltech.edu/I_30.html","http://www.feynmanlectures.caltech.edu/I_31.html","http://www.feynmanlectures.caltech.edu/I_32.html","http://www.feynmanlectures.caltech.edu/I_33.html","http://www.feynmanlectures.caltech.edu/I_34.html","http://www.feynmanlectures.caltech.edu/I_35.html","http://www.feynmanlectures.caltech.edu/I_36.html","http://www.feynmanlectures.caltech.edu/I_37.html","http://www.feynmanlectures.caltech.edu/I_38.html","http://www.feynmanlectures.caltech.edu/I_39.html","http://www.feynmanlectures.caltech.edu/I_40.html","http://www.feynmanlectures.caltech.edu/I_41.html","http://www.feynmanlectures.caltech.edu/I_42.html","http://www.feynmanlectures.caltech.edu/I_43.html","http://www.feynmanlectures.caltech.edu/I_44.html","http://www.feynmanlectures.caltech.edu/I_45.html","http://www.feynmanlectures.caltech.edu/I_46.html","http://www.feynmanlectures.caltech.edu/I_47.html","http://www.feynmanlectures.caltech.edu/I_48.html","http://www.feynmanlectures.caltech.edu/I_49.html","http://www.feynmanlectures.caltech.edu/I_50.html","http://www.feynmanlectures.caltech.edu/I_51.html","http://www.feynmanlectures.caltech.edu/I_52.html"]
}

get_urls.js

Goto = (vol,chap,sec) => {
    var volstrings =["I","II","III"];
    var dest;
    var chapstr = "0"+String(chap);
    chapstr = chapstr.substr(chapstr.length-2);
    dest = volstrings[vol-1] + "_" + chapstr + ".html"
    if(typeof(sec)!=='undefined') {
        dest += "#Ch" + String(chap) + "-S" + String(sec);
    }
    return (dest);
}

$('a.chapterlink').toArray().map(a => 'http://www.feynmanlectures.caltech.edu' + eval(a.href.split(':')[1]))

likely upstream (getbook) issue

I doubt it, given the getbook code hasn't changed in more than one year (yet someone above reported it works, apparently).

Could you try it yourself right now to see if it works? If it does work, can you please report the exact versions of your python and following packages:

Jinja2
MarkupSafe
Pillow
beautifulsoup4
certifi
chardet
getbook
html5lib
idna
lxml
python-dateutil
requests
six
soupsieve
urllib3
webencodings

For anyone who comes across this thread (as I just did), to fix this just:

pip install beautifulsoup4==4.6.0