IPython initially was a monolithic project that offered the notebook interface and the Python kernel in a single release. When the notebook interface was moved to a separate project, I suppose they kept the file extension for backwards compatibility.
but they spun off a whole new project -- lots of things were going to have to be created and changed anyways -- why keep this really strange, esoteric, five-letter filename extension unless you have a _really_ good reason.
that's probably the thing that bugs me most -- Jupyter looks really useful and fun and nerdy and wow, good job, y'all for creating it -- but what's up with the file extension that seems intended to be confusing?
if the idea seemed like it was going to have legs -- enough to spin off a new project -- then there were going to be more Jupyter notebooks CRUD'ed over each successive month than were ever created in total in the entire history of the project up to that point in time.
i guess most Windows users would never see the extension, most UI tools would not show the extension, and maybe most *nux users use command completion, so most folks would not really be affected too much.
but it just seems on the edge of ridiculous to me -- a troll job -- like, let's give this file format a windows95-like name, that'll be so nerdy and cool!
i'm cool with that to an extent, but grumpy old white guy part of me says 'nah'.
the .jpr filename extension doesn't seem to be overused. it _is_ pretty close to .jpg, which i guess might matter.
a .jup extension would potentially sound like a slur if you said it the wrong way, so no good, kind of like how dict() sounds, or the phrase 'premature optimization' -- which is a nonsensical/misleading anyways.
i don't know Jupyter well, so maybe there are a bunch of Jupyter-related artifacts/file types that would need to jockey for pole position for the .jpr extension.