The core part of this solution is creating the translation table. I am creating a one-to-one mapping between a character and its rotated character in the line string.maketrans(first, trance). So, after this A is mapped to N, B to O, etc.

After this, I am just translating the message based on above created translation table.

what does this code do exacly i dont understand it

but IT IS NOT...

If you're interested in micro-optimizations, that's fine. But at the very least, don't propagate false truths...

Hello,I am cool and you,too!

could have written res += num*num to make it look nicer

Similar to mine. This appeared to be the more faster.

Thanks I learnt from this solution but it doesn't pass the wild test

I tried again it works only with Python2

@FutureScience https://nedbatchelder.com/blog/201206/eval_really_is_dangerous.html. Eval is dangerous when it is casted upon user input but it is fine in the rest of the code as long as the string being evaluated is safe. In this context it is bad because it is evaulating an input parameter which the user can possibly change.

For example:

calc("5 1 2 + 4 * + 3 - 5 + __import__('os')._exit(0)") would exit the program.

Can you explain the exact meaning of "security issue"?

Eval is probably inadvisable because it puts a pretty bad security issue in your code.

I can verify. My solution does not produce the correct output for this proposed test case as well because 2/4 is not in its most simplified form, so it computes the lcm for 4, 5 and 7 when it really should be computing the lcm for 2, 5 and 7. Really good observation here--the question should be changed to also require the simplification of fractions, which would be a nice additional exercise.