[Sync Iteration] python/atbash-cipher/4

solutions/python/atbash-cipher/4/atbash_cipher.py

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+"""
+This is an implementation of the 'Atbash' cipher, an ancient
+encryption system created in the Middle East.
+"""
+
+import string
+
+alphabet: str = string.ascii_lowercase
+
+
+def encode(plain_text: str) -> str:
+    """
+    Encode text using the Atbash cipher.
+
+    Letters are mirrored in the lowercase Latin alphabet; digits are preserved.
+    Punctuation characters '.,!?' and spaces are removed. The result is grouped
+    into 5-character blocks separated by spaces for readability.
+
+    :param plain_text: Input text to encode.
+    :type plain_text: str
+    :returns: Encoded text (grouped in 5-character blocks when length >= 5).
+    :rtype: str
+    """
+    temp_txt: list[str] = [
+        _replace(char.lower()) for char in plain_text if char.isalnum()
+    ]
+    return " ".join(
+        "".join(temp_txt[i : i + 5]) for i in range(0, len(temp_txt), 5)
+    )
+
+
+def _replace(char: str) -> str:
+    """
+    Apply Atbash mapping to a single character.
+
+    Alphabetic characters are lowercased and mirrored in the alphabet;
+    non-letters are returned unchanged.
+
+    :param char: Character to transform.
+    :type char: str
+    :returns: Transformed character.
+    :rtype: str
+    """
+    if char.isalpha():
+        return alphabet[-(alphabet.index(char) + 1)]
+    return char
+
+
+def decode(ciphered_text: str) -> str:
+    """
+    Decode an Atbash-encoded string.
+
+    Atbash is symmetric; decoding reuses encoding and removes grouping spaces.
+
+    :param ciphered_text: Encoded text, optionally grouped with spaces.
+    :type ciphered_text: str
+    :returns: Decoded text without grouping spaces.
+    :rtype: str
+    """
+    return encode(ciphered_text).replace(" ", "")