Atbash Cipher

atbash-cipher/.exercism/config.json

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+{
+  "authors": [
+    "betegelse"
+  ],
+  "contributors": [
+    "behrtam",
+    "cmccandless",
+    "Dog",
+    "ikhadykin",
+    "jgomo3",
+    "kytrinyx",
+    "N-Parsons",
+    "parinporecha",
+    "pheanex",
+    "sjakobi",
+    "thomasjpfan",
+    "tqa236"
+  ],
+  "files": {
+    "solution": [
+      "atbash_cipher.py"
+    ],
+    "test": [
+      "atbash_cipher_test.py"
+    ],
+    "example": [
+      ".meta/example.py"
+    ]
+  },
+  "blurb": "Create an implementation of the Atbash cipher, an ancient encryption system created in the Middle East.",
+  "source": "Wikipedia",
+  "source_url": "https://en.wikipedia.org/wiki/Atbash"
+}

atbash-cipher/.exercism/metadata.json

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+{"track":"python","exercise":"atbash-cipher","id":"888b453465e64f5d91aea849caf4077c","url":"https://exercism.org/tracks/python/exercises/atbash-cipher","handle":"myFirstCode","is_requester":true,"auto_approve":false}

atbash-cipher/HELP.md

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+# Help
+
+## Running the tests
+
+We use [pytest][pytest: Getting Started Guide] as our website test runner.
+You will need to install `pytest` on your development machine if you want to run tests for the Python track locally.
+You should also install the following `pytest` plugins:
+
+- [pytest-cache][pytest-cache]
+- [pytest-subtests][pytest-subtests]
+
+Extended information can be found in our website [Python testing guide][Python track tests page].
+
+
+### Running Tests
+
+To run the included tests, navigate to the folder where the exercise is stored using `cd` in your terminal (_replace `{exercise-folder-location}` below with your path_).
+Test files usually end in `_test.py`, and are the same tests that run on the website when a solution is uploaded.
+
+Linux/MacOS
+```bash
+$ cd {path/to/exercise-folder-location}
+```
+
+Windows
+```powershell
+PS C:\Users\foobar> cd {path\to\exercise-folder-location}
+```
+
+<br>
+
+Next, run the `pytest` command in your terminal, replacing `{exercise_test.py}` with the name of the test file:
+
+Linux/MacOS
+```bash
+$ python3 -m pytest -o markers=task {exercise_test.py}
+==================== 7 passed in 0.08s ====================
+```
+
+Windows
+```powershell
+PS C:\Users\foobar> py -m pytest -o markers=task {exercise_test.py}
+==================== 7 passed in 0.08s ====================
+```
+
+
+### Common options
+- `-o` : override default `pytest.ini` (_you can use this to avoid marker warnings_)
+- `-v` : enable verbose output.
+- `-x` : stop running tests on first failure.
+- `--ff` : run failures from previous test before running other test cases.
+
+For additional options, use `python3 -m pytest -h` or `py -m pytest -h`.
+
+
+### Fixing warnings
+
+If you do not use `pytest -o markers=task` when invoking `pytest`, you might receive a `PytestUnknownMarkWarning` for tests that use our new syntax:
+
+```bash
+PytestUnknownMarkWarning: Unknown pytest.mark.task - is this a typo?  You can register custom marks to avoid this warning - for details, see https://docs.pytest.org/en/stable/mark.html
+```
+
+To avoid typing `pytest -o markers=task` for every test you run, you can use a `pytest.ini` configuration file.
+We have made one that can be downloaded from the top level of the Python track directory: [pytest.ini][pytest.ini].
+
+You can also create your own `pytest.ini` file with the following content:
+
+```ini
+[pytest]
+markers =
+    task: A concept exercise task.
+```
+
+Placing the `pytest.ini` file in the _root_ or _working_ directory for your Python track exercises will register the marks and stop the warnings.
+More information on pytest marks can be found in the `pytest` documentation on [marking test functions][pytest: marking test functions with attributes] and the `pytest` documentation on [working with custom markers][pytest: working with custom markers].
+
+Information on customizing pytest configurations can be found in the `pytest` documentation on [configuration file formats][pytest: configuration file formats].
+
+
+### Extending your IDE or Code Editor
+
+Many IDEs and code editors have built-in support for using `pytest` and other code quality tools.
+Some community-sourced options can be found on our [Python track tools page][Python track tools page].
+
+[Pytest: Getting Started Guide]: https://docs.pytest.org/en/latest/getting-started.html
+[Python track tools page]: https://exercism.org/docs/tracks/python/tools
+[Python track tests page]: https://exercism.org/docs/tracks/python/tests
+[pytest-cache]:http://pythonhosted.org/pytest-cache/
+[pytest-subtests]:https://github.com/pytest-dev/pytest-subtests
+[pytest.ini]: https://github.com/exercism/python/blob/main/pytest.ini
+[pytest: configuration file formats]: https://docs.pytest.org/en/6.2.x/customize.html#configuration-file-formats
+[pytest: marking test functions with attributes]: https://docs.pytest.org/en/6.2.x/mark.html#raising-errors-on-unknown-marks
+[pytest: working with custom markers]: https://docs.pytest.org/en/6.2.x/example/markers.html#working-with-custom-markers
+
+## Submitting your solution
+
+You can submit your solution using the `exercism submit atbash_cipher.py` command.
+This command will upload your solution to the Exercism website and print the solution page's URL.
+
+It's possible to submit an incomplete solution which allows you to:
+
+- See how others have completed the exercise
+- Request help from a mentor
+
+## Need to get help?
+
+If you'd like help solving the exercise, check the following pages:
+
+- The [Python track's documentation](https://exercism.org/docs/tracks/python)
+- The [Python track's programming category on the forum](https://forum.exercism.org/c/programming/python)
+- [Exercism's programming category on the forum](https://forum.exercism.org/c/programming/5)
+- The [Frequently Asked Questions](https://exercism.org/docs/using/faqs)
+
+Should those resources not suffice, you could submit your (incomplete) solution to request mentoring.
+
+Below are some resources for getting help if you run into trouble:
+
+- [The PSF](https://www.python.org) hosts Python downloads, documentation, and community resources.
+- [The Exercism Community on Discord](https://exercism.org/r/discord)
+- [Python Community on Discord](https://pythondiscord.com/) is a very helpful and active community.
+- [/r/learnpython/](https://www.reddit.com/r/learnpython/) is a subreddit designed for Python learners.
+- [#python on Libera.chat](https://www.python.org/community/irc/) this is where the core developers for the language hang out and get work done.
+- [Python Community Forums](https://discuss.python.org/)
+- [Free Code Camp Community Forums](https://forum.freecodecamp.org/)
+- [CodeNewbie Community Help Tag](https://community.codenewbie.org/t/help)
+- [Pythontutor](http://pythontutor.com/) for stepping through small code snippets visually.
+
+Additionally, [StackOverflow](http://stackoverflow.com/questions/tagged/python) is a good spot to search for your problem/question to see if it has been answered already.
+ If not - you can always [ask](https://stackoverflow.com/help/how-to-ask) or [answer](https://stackoverflow.com/help/how-to-answer) someone else's question.

atbash-cipher/README.md

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+# Atbash Cipher
+
+Welcome to Atbash Cipher on Exercism's Python Track.
+If you need help running the tests or submitting your code, check out `HELP.md`.
+
+## Instructions
+
+Create an implementation of the Atbash cipher, an ancient encryption system created in the Middle East.
+
+The Atbash cipher is a simple substitution cipher that relies on transposing all the letters in the alphabet such that the resulting alphabet is backwards.
+The first letter is replaced with the last letter, the second with the second-last, and so on.
+
+An Atbash cipher for the Latin alphabet would be as follows:
+
+```text
+Plain:  abcdefghijklmnopqrstuvwxyz
+Cipher: zyxwvutsrqponmlkjihgfedcba
+```
+
+It is a very weak cipher because it only has one possible key, and it is a simple mono-alphabetic substitution cipher.
+However, this may not have been an issue in the cipher's time.
+
+Ciphertext is written out in groups of fixed length, the traditional group size being 5 letters, leaving numbers unchanged, and punctuation is excluded.
+This is to make it harder to guess things based on word boundaries.
+All text will be encoded as lowercase letters.
+
+## Examples
+
+- Encoding `test` gives `gvhg`
+- Encoding `x123 yes` gives `c123b vh`
+- Decoding `gvhg` gives `test`
+- Decoding `gsvjf rxpyi ldmul cqfnk hlevi gsvoz abwlt` gives `thequickbrownfoxjumpsoverthelazydog`
+
+## Source
+
+### Created by
+
+- @betegelse
+
+### Contributed to by
+
+- @behrtam
+- @cmccandless
+- @Dog
+- @ikhadykin
+- @jgomo3
+- @kytrinyx
+- @N-Parsons
+- @parinporecha
+- @pheanex
+- @sjakobi
+- @thomasjpfan
+- @tqa236
+
+### Based on
+
+Wikipedia - https://en.wikipedia.org/wiki/Atbash

atbash-cipher/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: [str] = [
+        _replace(char) for char in plain_text if char not in ".,!? "
+    ]
+    if len(temp_txt) > 4:
+        step: int = 5
+        i_start: int = 0
+        i_end: int = i_start + step
+        txt: list[str] = []
+        while i_start <= len(temp_txt):
+            tmp: str = "".join(temp_txt[i_start:i_end])
+            if tmp:
+                txt.append(tmp)
+            i_start, i_end = i_end, i_end + step
+        return " ".join(txt)
+    return "".join(temp_txt)
+
+
+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.lower().isalpha():
+        return alphabet[-(alphabet.index(char.lower()) + 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(" ", "")

atbash-cipher/atbash_cipher_test.py

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+# pylint: disable=C0301, C0114, C0115, C0116, R0904
+# These tests are auto-generated with test data from:
+# https://github.com/exercism/problem-specifications/tree/main/exercises/atbash-cipher/canonical-data.json
+# File last updated on 2023-07-20
+
+import unittest
+
+from atbash_cipher import (
+    decode,
+    encode,
+)
+
+
+class AtbashCipherTest(unittest.TestCase):
+    def test_encode_yes(self):
+        self.assertEqual(encode("yes"), "bvh")
+
+    def test_encode_no(self):
+        self.assertEqual(encode("no"), "ml")
+
+    def test_encode_omg(self):
+        self.assertEqual(encode("OMG"), "lnt")
+
+    def test_encode_spaces(self):
+        self.assertEqual(encode("O M G"), "lnt")
+
+    def test_encode_mindblowingly(self):
+        self.assertEqual(encode("mindblowingly"), "nrmwy oldrm tob")
+
+    def test_encode_numbers(self):
+        self.assertEqual(encode("Testing,1 2 3, testing."), "gvhgr mt123 gvhgr mt")
+
+    def test_encode_deep_thought(self):
+        self.assertEqual(encode("Truth is fiction."), "gifgs rhurx grlm")
+
+    def test_encode_all_the_letters(self):
+        self.assertEqual(
+            encode("The quick brown fox jumps over the lazy dog."),
+            "gsvjf rxpyi ldmul cqfnk hlevi gsvoz abwlt",
+        )
+
+    def test_decode_exercism(self):
+        self.assertEqual(decode("vcvix rhn"), "exercism")
+
+    def test_decode_a_sentence(self):
+        self.assertEqual(
+            decode("zmlyh gzxov rhlug vmzhg vkkrm thglm v"),
+            "anobstacleisoftenasteppingstone",
+        )
+
+    def test_decode_numbers(self):
+        self.assertEqual(decode("gvhgr mt123 gvhgr mt"), "testing123testing")
+
+    def test_decode_all_the_letters(self):
+        self.assertEqual(
+            decode("gsvjf rxpyi ldmul cqfnk hlevi gsvoz abwlt"),
+            "thequickbrownfoxjumpsoverthelazydog",
+        )
+
+    def test_decode_with_too_many_spaces(self):
+        self.assertEqual(decode("vc vix    r hn"), "exercism")
+
+    def test_decode_with_no_spaces(self):
+        self.assertEqual(
+            decode("zmlyhgzxovrhlugvmzhgvkkrmthglmv"), "anobstacleisoftenasteppingstone"
+        )