Using List for Accumulation:
Instead of string concatenation within the loop, result.append() is used to create a list, and join is called at the end to concatenate the list into a string. This is more efficient for larger strings.
Removed Unnecessary Parameter n:
Eliminating the n parameter makes the function simpler and ensures consistent ROT13 encryption/decryption.
Refactored Doctest and Assertions:
The doctest examples are consistent with the revised function, ensuring reversibility through dencrypt(dencrypt(s)) == s without additional parameters.