hey, thanks!

it's actually not a binary or, but a union operator. the syntax was added to python 3.9 as a way to combine two dictionas a way to combine two dictionaries.

If you're interested, here's the details:
https://peps.python.org/pep-0584/

look at all these numbers:

1987 all unique
1988 has two 8s
1989 has two 9s
1990 has two 9s
1991 has two 9s
1992 has two 9s
1993 has two 9s
1994 has two 9s
1995 has two 9s
1996 has two 9s
1997 has two 9s
1998 has two 9s
1999 has two 9s
2000 has two 0s
2001 has two 0s
2002 has two 0s
2003 has two 0s
2004 has two 0s
2005 has two 0s
2006 has two 0s
2007 has two 0s
2008 has two 0s
2009 has two 0s
2010 has two 0s
2011 has two 1s
2012 has two 2s
2013 all unique

I'm not sure about the subtleties of big O, however (and I could be wrong about this) but I note that this solution creates a total of four new string objects & two new list objects, which all require some level of "under the hood" iterations, whereas my solution creates none of those new objects, and only iterates through the input string once. Meanwhile, I am very curious about how my Python code would be judged because the style is not exactly Pythonic. Any feedback would be most appreciated.

Please use spoiler flag next time.