Hide input cells #32. That would make the ability to mix hidden python stuff with purposefully displayed python. I struggled with this, too. My first attempt was for a talk at EuroPython 2014 (Brainwaves for Hackers) where I hacked the live_reveal extension to interpret skip (from the slideshow-toolbar) as hide input.
An ISO file is a complete copy of a CD or DVD. You can create ISO images yourself or download them from the Internet. For example, Linux distributions offer freely downloadable ISO files that you can burn to disc. You can use an ISO image in a variety of ways. The ISO file itself is a backup of a disc, so you can use the ISO file if you ever lose or damage the original disc CDs Are Not Forever: The Truth About CD/DVD Longevity, Mold & Rot .
Many applications that can be used with ZIP files can also be used with ISO files, so you may already have such an application available. Your application might use the word decompress rather than extract or unzip, but the result is the same. You need additional software to extract an ISO file.