Project: Find the median

Write a function named find_median that takes a list of numbers and returns their median. You will need to sort the list first. If you are not sure how the median works, look it up before you start.

list_of_nums = [13, 7, -3, 82, 4]
result = find_median(list_of_nums)

Save the file as find_median.py.

Show a solution

Try the project on your own first. This is one working solution, followed by its tests. Press Run to run the tests. Read them to see what thorough testing looks like, then change the solution and run again to watch a test fail. The testing tools used here (classes and unittest) are not part of the course yet, so do not worry about how they work.

def find_median(numbers: list) -> float:
    """Return the median of a list of numbers without changing the list."""
    ordered: list = numbers[:]
    ordered.sort()
    middle: int = len(ordered) // 2
    if len(ordered) % 2 == 0:
        return (ordered[middle - 1] + ordered[middle]) / 2
    return ordered[middle]

# ---- Tests ----
import sys
import unittest

class TestFindMedian(unittest.TestCase):
    def test_a_single_number_is_its_own_median(self):
        self.assertEqual(find_median([5]), 5)

def test_an_odd_length_list_returns_the_middle_number(self):
        self.assertEqual(find_median([1, 2, 3]), 2)

def test_the_example_from_the_project(self):
        self.assertEqual(find_median([13, 7, -3, 82, 4]), 7)

def test_an_even_length_list_averages_the_two_middle_numbers(self):
        self.assertEqual(find_median([1, 2, 3, 4]), 2.5)

def test_two_numbers_average_to_the_value_between_them(self):
        self.assertEqual(find_median([10, 20]), 15)

def test_an_even_length_list_can_have_a_median_that_is_not_in_the_list(self):
        self.assertEqual(find_median([1, 2, 3, 10, 20, 30]), 6.5)

def test_an_unsorted_list_is_sorted_first(self):
        self.assertEqual(find_median([9, 1, 5, 3, 7]), 5)
        self.assertEqual(find_median([8, 2, 6, 4]), 5)

def test_negative_numbers_are_handled(self):
        self.assertEqual(find_median([-5, -1, -3]), -3)
        self.assertEqual(find_median([-4, -2]), -3)

def test_repeated_numbers_are_handled(self):
        self.assertEqual(find_median([4, 4, 4, 9]), 4)

def test_the_original_list_is_left_unchanged(self):
        numbers = [13, 7, -3, 82, 4]
        find_median(numbers)
        self.assertEqual(numbers, [13, 7, -3, 82, 4])

# ---- Run the tests ----
loader = unittest.defaultTestLoader
suite = unittest.TestSuite(loader.loadTestsFromTestCase(case) for case in [TestFindMedian])
unittest.TextTestRunner(stream=sys.stdout, verbosity=2).run(suite)

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