Then just a comment that say that `16` is "random". That the kind of things you can wonder when you came across that later, like, it might be to avoid new line, you might want `len('Notebook does not appear to be JSON:')+n < 80' to fit on terminal screen..

And for aestetic purpose add a '...' , I guess we can suppose we will never be in a case where the file is smaller than 16 char or empty.