Why is PEP-801 reserved?

Warning, this is supposition, though investigated as at least being plausible.

If you look at the history for the python\peps\pep0 file (the listing of all PEPs), you'll find the change was done in October 2013 by one Barry Warsaw, so probably nothing to do with any Polish Python user group as some surmise :-)

I can really only suggest why I would have done such a thing and, based on that, the most likely reason for it would be to either test that the changes would work with some random value, or that a placeholder of some sort was needed. Short of asking the author himself (which I have now done, so stay tuned ...), that's probably the most likely reason for now.

After receiving a reply from the author, the reason is as simple as it was related to some song/band back in those days, possibly this one. The email reply follows:

You’ve both reached out to me about the same topic and SO thread, so Ihope you don’t mind me responding to you both. First, thanks for yourlove of Python! It’s a fantastic language, and even better community,and it’s been a great place to have spent the better part of myprofessional career.

What better than a minor mystery in a corner of a language? Python,named after the Monty Python troupe, has a rich history of humor andeaster eggs, so 801 could be nothing more than that. An enigma,wrapped in a riddle, stuffed into a conundrum. A turducken PEP.

Maybe you’re right, and it’s the secret key that unlocks the PolishPython Ploy, a conspiracy of Warsawans to take over the language fromthe Dastardly Dutch Dozen. Or it could be a number, that when fed toa certain Python stdlib API, takes over your speakers and unstoppablyplays the entire series of Flying Circus until you Silly Walkaccurately in front of your webcam.

I like to think it’s just a fun number that named a song and a bandsome people were into back in the day, coupled with the abuse of powerfrom a mad PEP editor everyone else is too afraid to question. Onlythe Python Secret Underground (PSU) -which emphatically does notexist- knows for sure.

Cheers,
-Barry

Some PEPs are not numbered sequentially, but are numbered based on their content. Examples are:

• PEP 628 adding math.tau, so named because tau is approximately 6.28,
• PEP 754, implementing the IEEE 754 standard, named after the standard number

Now what if I want to start writing a PEP, I desire for it to have a special number, but I haven't written it yet? Then we can ask the PEP manager! On 21 June 2018, PEP numbers 801 was reserved in this pull request. Initially, PEP 581 was reserved as well, but this reservation was withdrawn.

So, presumably people reserved PEP 801 and 581 because they are preparing a PEP for which this number has a special meaning, and they don't want that number to be assigned to any other PEP.