join() function joins the elements of the list (in this case ans) together using the string (in this case empty string ''), while lower() changes all characters to lower case.

ahh, I must've been blind, thanks!

Maybe it's just me, but the description "... if we rotate one or more characters to the left. " was a bit misleading as I started out moving the characters individually to the left (and I didn't understand why "abcabc" couldn't be a palindrome). My suggestion would be to replace it with " ...if we rotate the string.", as having "left" there doesn't really have any significance since you don't have a constraint on the number of rotations.
Good work btw, I liked the kata!