If you didn't know, Symmetry454 is a proposal for the reform of the Gregorian calendar made in 2002 that, as the name implies, has months that alternate between four and five weeks. It is perennial, meaning weekdays of dates don't change (so you can reuse calendars as long as it's not a leap year!) and certain holidays that depend on the nth weekday would have fixed dates (like Easter is proposed to be on the 7th of April). It interestingly has a leap week system that alternates between 5 and 6 year gaps between leap years, with an additional week being added to December during leap years. Personally, I find a leap week far more fun than a leap day.
I have made a small Python script that converts Gregorian dates into Symmetry454 dates, which follows the steps noted by the person who made Symmetry454 (they had a whole PDF and everything explaining each step to calculate all that, super helpful!). Currently, it accepts Gregorian dates (year, month, and day) and returns the Symmetry454 date (in YYYY-MM-DD format), as well as some additional information (like a basic calendar that shows the position of the day in the month. There is also a function for outputting a year, what quarter the day is in, and the fixed date since a defined epoch)
It doesn't really do much at the moment, but in the future, I would like the program to be able to let the user explore the calendar of different Symmetry454 years, as well as easily interconvert the dates of the two systems. There are probably a bunch of bugs in my code, and it's not really all that practical, but making it has been pretty fun!
If you want to check it out, it's on Codeberg with the GPLv3 license: https://codeberg.org/sbird/py-symmetry454
The PDF found in this website detailing the calculations for converting from Gregorian to Symmetry454 was very helpful, here it is for reference: https://kalendis.free.nf/symmetry.htm (go all the way down to "Documentation", it's the PDF labelled "calendar arithmetic")
No AI was used to create this project, all mistakes and bugginess are my own.