Assumming a is a string. The Slice notation in python has the syntax -
So, when you do a[::-1] , it starts from the end, towards the first, taking each element. So it reverses a. This is applicable for lists/tuples as well.
>>> a = '1232' >>> a[::-1] '2321'
Then you convert it to int and then back to string (Though not sure why you do that) , that just gives you back the string.