good job

I'm just writing back now. What kind of trick is this?

its nice

I think @AndrewB31415 was suggesting that there is a different approach that doesn't require iterating through a string of the input (*see his solution). But if you use this approach then you do need to convert the input number to an iterable.

You're right... these things are not taught at schools too much. The emergence of computing brought to light some aspects of math that were less stressed before: Graph theory, Number Theory, Combinatorics, Discrete Math etc. Usually these topics are not well adressed in schools - the highschool curriculum (in many countries) is focused on algebra, calculus and geometry, and more suitable for learning physics or economics or engineering than computers.
And how needed are those hacks? when playing competitive programming or here on this site or maybe at some job interview - these tricks are awesome going from O(n) or O(n2) to easy one liner O(1)... I doubt how needed they are in real life programming. Probably not much, and if you ever need them, google them out

Except this doesn't work for numbers greater than 9. See my solution for one that does

you and me with the for loop, while loop, count combo <3

I don't think using the count method for each element is very natural. It is pretty expensive

You probably mastered regex now?

how evaluation go once for this ?

pop(0) would have done the same magic without needing to reverse the list but i can't complain because my solution is way longer lol

Yeah, but you need a proof by induction to do that. Did you do one yourself or (like "plebs") take it from the internet?

OP's solution is better imo. More readable, and doesn't add clutter (Not that yours does)