run length encoding exercise

python/run-length-encoding/.exercism/metadata.json

@@ -0,0 +1 @@
+{"track":"python","exercise":"run-length-encoding","id":"d794356bb2f64e1998420f4ed754c3e0","url":"https://exercism.io/my/solutions/d794356bb2f64e1998420f4ed754c3e0","handle":"Xevion","is_requester":true,"auto_approve":false}

python/run-length-encoding/README.md

@@ -0,0 +1,73 @@
+# Run Length Encoding
+
+Implement run-length encoding and decoding.
+
+Run-length encoding (RLE) is a simple form of data compression, where runs
+(consecutive data elements) are replaced by just one data value and count.
+
+For example we can represent the original 53 characters with only 13.
+
+```text
+"WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWB"  ->  "12WB12W3B24WB"
+```
+
+RLE allows the original data to be perfectly reconstructed from
+the compressed data, which makes it a lossless data compression.
+
+```text
+"AABCCCDEEEE"  ->  "2AB3CD4E"  ->  "AABCCCDEEEE"
+```
+
+For simplicity, you can assume that the unencoded string will only contain
+the letters A through Z (either lower or upper case) and whitespace. This way
+data to be encoded will never contain any numbers and numbers inside data to
+be decoded always represent the count for the following character.
+
+## Exception messages
+
+Sometimes it is necessary to raise an exception. When you do this, you should include a meaningful error message to
+indicate what the source of the error is. This makes your code more readable and helps significantly with debugging. Not
+every exercise will require you to raise an exception, but for those that do, the tests will only pass if you include
+a message.
+
+To raise a message with an exception, just write it as an argument to the exception type. For example, instead of
+`raise Exception`, you should write:
+
+```python
+raise Exception("Meaningful message indicating the source of the error")
+```
+
+## Running the tests
+
+To run the tests, run the appropriate command below ([why they are different](https://github.com/pytest-dev/pytest/issues/1629#issue-161422224)):
+
+- Python 2.7: `py.test run_length_encoding_test.py`
+- Python 3.4+: `pytest run_length_encoding_test.py`
+
+Alternatively, you can tell Python to run the pytest module (allowing the same command to be used regardless of Python version):
+`python -m pytest run_length_encoding_test.py`
+
+### Common `pytest` options
+
+- `-v` : enable verbose output
+- `-x` : stop running tests on first failure
+- `--ff` : run failures from previous test before running other test cases
+
+For other options, see `python -m pytest -h`
+
+## Submitting Exercises
+
+Note that, when trying to submit an exercise, make sure the solution is in the `$EXERCISM_WORKSPACE/python/run-length-encoding` directory.
+
+You can find your Exercism workspace by running `exercism debug` and looking for the line that starts with `Workspace`.
+
+For more detailed information about running tests, code style and linting,
+please see [Running the Tests](http://exercism.io/tracks/python/tests).
+
+## Source
+
+Wikipedia [https://en.wikipedia.org/wiki/Run-length_encoding](https://en.wikipedia.org/wiki/Run-length_encoding)
+
+## Submitting Incomplete Solutions
+
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.

python/run-length-encoding/run_length_encoding.py

@@ -0,0 +1,7 @@
+import re
+
+def encode(string):
+    return ''.join(map(lambda item : '{}{}'.format(len(item.group(0)), item.group(0)[0]) if len(item.group(0)) > 1 else item.group(0), re.finditer(re.compile(r'(.)\1{0,}'), string)))
+
+def decode(string):
+    return ''.join([sub[-1] * int(sub[:-1]) if len(sub) >= 2 else sub for sub in re.findall(re.compile(r'(\d*.)'), string)])

python/run-length-encoding/run_length_encoding_test.py

@@ -0,0 +1,54 @@
+import unittest
+
+from run_length_encoding import encode, decode
+
+
+# Tests adapted from `problem-specifications//canonical-data.json` @ v1.1.0
+
+class RunLengthEncodingTest(unittest.TestCase):
+    def test_encode_empty_string(self):
+        self.assertMultiLineEqual(encode(''), '')
+
+    def test_encode_single_characters_only_are_encoded_without_count(self):
+        self.assertMultiLineEqual(encode('XYZ'), 'XYZ')
+
+    def test_encode_string_with_no_single_characters(self):
+        self.assertMultiLineEqual(encode('AABBBCCCC'), '2A3B4C')
+
+    def test_encode_single_characters_mixed_with_repeated_characters(self):
+        self.assertMultiLineEqual(
+            encode('WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWB'),
+            '12WB12W3B24WB')
+
+    def test_encode_multiple_whitespace_mixed_in_string(self):
+        self.assertMultiLineEqual(encode('  hsqq qww  '), '2 hs2q q2w2 ')
+
+    def test_encode_lowercase_characters(self):
+        self.assertMultiLineEqual(encode('aabbbcccc'), '2a3b4c')
+
+    def test_decode_empty_string(self):
+        self.assertMultiLineEqual(decode(''), '')
+
+    def test_decode_single_characters_only(self):
+        self.assertMultiLineEqual(decode('XYZ'), 'XYZ')
+
+    def test_decode_string_with_no_single_characters(self):
+        self.assertMultiLineEqual(decode('2A3B4C'), 'AABBBCCCC')
+
+    def test_decode_single_characters_with_repeated_characters(self):
+        self.assertMultiLineEqual(
+            decode('12WB12W3B24WB'),
+            'WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWB')
+
+    def test_decode_multiple_whitespace_mixed_in_string(self):
+        self.assertMultiLineEqual(decode('2 hs2q q2w2 '), '  hsqq qww  ')
+
+    def test_decode_lower_case_string(self):
+        self.assertMultiLineEqual(decode('2a3b4c'), 'aabbbcccc')
+
+    def test_combination(self):
+        self.assertMultiLineEqual(decode(encode('zzz ZZ  zZ')), 'zzz ZZ  zZ')
+
+
+if __name__ == '__main__':
+    unittest.main()