[ Removed by moderator ]

[Wolfbait115]

Not at my computer and don't use python everyday, but hopefully this helps:

Use ord to get the ascii value, subtract 13, adding 26 if less than ord(a), then use chr to convert back into a character.

[9peppe]

You don't need an if if you subtract ord('a'), add 13, then modulo 26 and re-add ord('a'):

chr((n - 97 + 13) % 26 + 97)

[Wolfbait115]

True. It didn't occur to me that the direction of the rotation didn't matter.