From 40c55cd0e55930e1d88fe4ed431986030722d13e Mon Sep 17 00:00:00 2001
From: zimmersandro <sandro.zimmermann@stud.fhgr.ch>
Date: Tue, 23 Jun 2026 21:24:36 +0200
Subject: [PATCH] chore:  added kata description. feat: kata rot13, which is a
 cesar cipher with 13 letter shift. test: test cases for kata rot13.

---
 README.md                          |  3 ++-
 src/codewars/kata_rot13.py         | 22 ++++++++++++++++++++++
 tests/tests_codewars/test_rot13.py | 14 ++++++++++++++
 3 files changed, 38 insertions(+), 1 deletion(-)
 create mode 100644 src/codewars/kata_rot13.py
 create mode 100644 tests/tests_codewars/test_rot13.py

diff --git a/README.md b/README.md
index dd10e4f..8225755 100644
--- a/README.md
+++ b/README.md
@@ -33,4 +33,5 @@ Repository for CDS-2020 Programming and Promt Engineering II
 |Chinese Numeral Encoder|kata_chinese_numeral_encoder.py|test_chinese_numeral_encoder.py|[52608f5345d4a19bed000b31](https://www.codewars.com/kata/52608f5345d4a19bed000b31)|
 |RGB To Hex Conversion|kata_rgb_2_hex.py|test_rgb_2_hex.py|[513e08acc600c94f01000001](https://www.codewars.com/kata/513e08acc600c94f01000001)|
 |Most frequently used words in a text|kata_most_words_used.py|test_most_words_used.py|[51e056fe544cf36c410000fb](https://www.codewars.com/kata/51e056fe544cf36c410000fb)|
-|Simple Fun #128: Doubly Not Less|kata_doubly_not_less.py|test_doubly_not_less.py|[58a3ea0a8bdda5093800000e](https://www.codewars.com/kata/58a3ea0a8bdda5093800000e)|
\ No newline at end of file
+|Simple Fun #128: Doubly Not Less|kata_doubly_not_less.py|test_doubly_not_less.py|[58a3ea0a8bdda5093800000e](https://www.codewars.com/kata/58a3ea0a8bdda5093800000e)|
+|Rot13|kata_rot13.py|test_rot13.py|[530e15517bc88ac656000716](https://www.codewars.com/kata/530e15517bc88ac656000716/)|
diff --git a/src/codewars/kata_rot13.py b/src/codewars/kata_rot13.py
new file mode 100644
index 0000000..852c339
--- /dev/null
+++ b/src/codewars/kata_rot13.py
@@ -0,0 +1,22 @@
+ALPHABET = "abcdefghijklmnopqrstuvwxyz"
+
+
+def rot13(s):
+    cipher = []
+
+    for c in s:
+        make_upper = c.isupper()
+        c = c.lower()
+
+        if c.isalpha():
+            i = (ALPHABET.index(c) + 13) % 26
+            new_s = ALPHABET[i]
+
+            if make_upper:
+                new_s = new_s.upper()
+
+            cipher.append(new_s)
+        else:
+            cipher.append(c)
+
+    return "".join(cipher)
diff --git a/tests/tests_codewars/test_rot13.py b/tests/tests_codewars/test_rot13.py
new file mode 100644
index 0000000..b28ca0e
--- /dev/null
+++ b/tests/tests_codewars/test_rot13.py
@@ -0,0 +1,14 @@
+from src.codewars.kata_rot13 import rot13
+import pytest
+
+
+@pytest.mark.parametrize(
+    ("s", "expected"),
+    [
+        ("test", "grfg"),
+        ("Test", "Grfg"),
+        ("aA bB zZ 1234 *!?%", "nN oO mM 1234 *!?%"),
+    ],
+)
+def test_rot13(s, expected):
+    assert rot13(s) == expected