Update rot13.py

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.

ciphers/rot13.py

@@ -1,37 +1,36 @@
-def dencrypt(s: str, n: int = 13) -> str:
+def dencrypt(s: str) -> str:
     """
-    https://en.wikipedia.org/wiki/ROT13
+    Applies ROT13 encryption or decryption to the input string.
-
+    
+    Example usage:
     >>> msg = "My secret bank account number is 173-52946 so don't tell anyone!!"
-    >>> s = dencrypt(msg)
+    >>> encrypted = dencrypt(msg)
-    >>> s
+    >>> encrypted
     "Zl frperg onax nppbhag ahzore vf 173-52946 fb qba'g gryy nalbar!!"
-    >>> dencrypt(s) == msg
+    >>> dencrypt(encrypted) == msg
     True
     """
-    out = ""
+    result = []
     for c in s:
         if "A" <= c <= "Z":
-            out += chr(ord("A") + (ord(c) - ord("A") + n) % 26)
+            result.append(chr(ord("A") + (ord(c) - ord("A") + 13) % 26))
         elif "a" <= c <= "z":
-            out += chr(ord("a") + (ord(c) - ord("a") + n) % 26)
+            result.append(chr(ord("a") + (ord(c) - ord("a") + 13) % 26))
         else:
-            out += c
+            result.append(c)
-    return out
+    return "".join(result)
-
 
 def main() -> None:
     s0 = input("Enter message: ")
 
-    s1 = dencrypt(s0, 13)
+    s1 = dencrypt(s0)
     print("Encryption:", s1)
 
-    s2 = dencrypt(s1, 13)
+    s2 = dencrypt(s1)
     print("Decryption: ", s2)
 
 
 if __name__ == "__main__":
     import doctest
-
     doctest.testmod()
     main()