Take a nested list and return a single flattened list with all values except nil/null.
The challenge is to write a function that accepts an arbitrarily-deep nested list-like structure and returns a flattened structure without any nil/null values.
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:
raise Exception("Meaningful message indicating the source of the error")
To run the tests, run the appropriate command below (why they are different):
Alternatively, you can tell Python to run the pytest module (allowing the same command to be used regardless of Python version):
python -m pytest flatten_array_test.py
-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
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Interview Question https://reference.wolfram.com/language/ref/Flatten.html
It's possible to submit an incomplete solution so you can see how others have completed the exercise.
import unittest from flatten_array import flatten # Tests adapted from `problem-specifications//canonical-data.json` @ v1.2.0 class FlattenArrayTest(unittest.TestCase): def test_no_nesting(self): self.assertEqual(flatten([0, 1, 2]), [0, 1, 2]) def test_flatten_integers(self): inputs = [1, [2, 3, 4, 5, 6, 7], 8] expected = [1, 2, 3, 4, 5, 6, 7, 8] self.assertEqual(flatten(inputs), expected) def test_five_level_nesting(self): inputs = [0, 2, [[2, 3], 8, 100, 4, [[]]], -2] expected = [0, 2, 2, 3, 8, 100, 4, 50, -2] self.assertEqual(flatten(inputs), expected) def test_six_level_nesting(self): inputs = [1, [2, [], [4, []], 6, 7], 8] expected = [1, 2, 3, 4, 5, 6, 7, 8] self.assertEqual(flatten(inputs), expected) def test_with_none_values(self): inputs = [0, 2, [[2, 3], 8, [], None, [[None]]], -2] expected = [0, 2, 2, 3, 8, 100, -2] self.assertEqual(flatten(inputs), expected) def test_all_values_are_none(self): inputs = [None, [[[None]]], None, None, [[None, None], None], None] expected =  self.assertEqual(flatten(inputs), expected) # Additional tests for this track def test_empty_nested_lists(self): self.assertEqual(flatten([[()]]), ) def test_strings(self): self.assertEqual(flatten(['0', ['1', '2']]), ['0', '1', '2']) if __name__ == '__main__': unittest.main()
def flatten(nested_list): return [element for element in flatten_list(nested_list)] def flatten_list(nested_list): for element in nested_list: if not isinstance(element, list): if element is not None and not isinstance(element, tuple): yield element else: for subelement in flatten_list(element): yield subelement
A huge amount can be learned from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.
Here are some questions to help you reflect on this solution and learn the most from it.