I don't think the parenthesis around the modulos are serving any purpose here. They can be removed

It's so simple!

odd and even variables can be strings instead of lists, and use += instead of append. That will eliminate the join step at the end

ohh, using the index as the number was clever indeed

this solution would not work if different negative value other than -1 was found in dict.values(), but none of the test cases cover that scenario

I'm not clear why sumrev[3::-1] on the second to last line works. I had it on sumrev[1::-1], but 1 test out of 121 was failing until I changed it.

this is quite a clean solution

thank you so much! I've been stuck on this for ages.

TIL it doesn't need to be a string for .format() to accept it.
my for loop was entirely unneeded