collatz conjecture exercise w/ f-string method & no parentheses

python/collatz-conjecture/.exercism/metadata.json

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+{"track":"python","exercise":"collatz-conjecture","id":"ce1c77cfccd84f15be130ca55382058e","url":"https://exercism.io/my/solutions/ce1c77cfccd84f15be130ca55382058e","handle":"Xevion","is_requester":true,"auto_approve":false}

python/collatz-conjecture/README.md

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+# Collatz Conjecture
+
+The Collatz Conjecture or 3x+1 problem can be summarized as follows:
+
+Take any positive integer n. If n is even, divide n by 2 to get n / 2. If n is
+odd, multiply n by 3 and add 1 to get 3n + 1. Repeat the process indefinitely.
+The conjecture states that no matter which number you start with, you will
+always reach 1 eventually.
+
+Given a number n, return the number of steps required to reach 1.
+
+## Examples
+
+Starting with n = 12, the steps would be as follows:
+
+0. 12
+1. 6
+2. 3
+3. 10
+4. 5
+5. 16
+6. 8
+7. 4
+8. 2
+9. 1
+
+Resulting in 9 steps. So for input n = 12, the return value would be 9.
+
+## Notes
+
+The Collatz Conjecture is only concerned with strictly positive integers, so your solution should raise a `ValueError` with a meaningful message if given 0 or a negative integer.
+
+
+## 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 collatz_conjecture_test.py`
+- Python 3.4+: `pytest collatz_conjecture_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 collatz_conjecture_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/collatz-conjecture` 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
+
+An unsolved problem in mathematics named after mathematician Lothar Collatz [https://en.wikipedia.org/wiki/3x_%2B_1_problem](https://en.wikipedia.org/wiki/3x_%2B_1_problem)
+
+## Submitting Incomplete Solutions
+
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.

python/collatz-conjecture/collatz_conjecture.py

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+steps = lambda x, s=0 : exec(f'raise ValueError(\'Value \\\'{x}\\\' is not a valid Collatz Sequence starting point.\')') if x < 1 else s if x == 1 else steps(x // 2, s+1) if x % 2 == 0 else steps((3 * x) + 1, s+1)

python/collatz-conjecture/collatz_conjecture_test.py

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+import unittest
+
+from collatz_conjecture import steps
+
+
+# Tests adapted from `problem-specifications//canonical-data.json` @ v1.2.1
+
+
+class CollatzConjectureTest(unittest.TestCase):
+    def test_zero_steps_for_one(self):
+        self.assertEqual(steps(1), 0)
+
+    def test_divide_if_even(self):
+        self.assertEqual(steps(16), 4)
+
+    def test_even_and_odd_steps(self):
+        self.assertEqual(steps(12), 9)
+
+    def test_large_number_of_even_and_odd_steps(self):
+        self.assertEqual(steps(1000000), 152)
+
+    def test_zero_is_an_error(self):
+        with self.assertRaisesWithMessage(ValueError):
+            steps(0)
+
+    def test_negative_value_is_an_error(self):
+        with self.assertRaisesWithMessage(ValueError):
+            steps(-15)
+
+    # Utility functions
+    def setUp(self):
+        try:
+            self.assertRaisesRegex
+        except AttributeError:
+            self.assertRaisesRegex = self.assertRaisesRegexp
+
+    def assertRaisesWithMessage(self, exception):
+        return self.assertRaisesRegex(exception, r".+")
+
+
+if __name__ == "__main__":
+    unittest.main()