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to Raindrops in the Python Track

Published at May 09 2020 · 0 comments
Test suite


This exercise has changed since this solution was written.

Your task is to convert a number into a string that contains raindrop sounds corresponding to certain potential factors. A factor is a number that evenly divides into another number, leaving no remainder. The simplest way to test if a one number is a factor of another is to use the modulo operation.

The rules of raindrops are that if a given number:

  • has 3 as a factor, add 'Pling' to the result.
  • has 5 as a factor, add 'Plang' to the result.
  • has 7 as a factor, add 'Plong' to the result.
  • does not have any of 3, 5, or 7 as a factor, the result should be the digits of the number.


  • 28 has 7 as a factor, but not 3 or 5, so the result would be "Plong".
  • 30 has both 3 and 5 as factors, but not 7, so the result would be "PlingPlang".
  • 34 is not factored by 3, 5, or 7, so the result would be "34".

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:

raise Exception("Meaningful message indicating the source of the error")

Running the tests

To run the tests, run pytest raindrops_test.py

Alternatively, you can tell Python to run the pytest module: python -m pytest raindrops_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/raindrops 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.


A variation on FizzBuzz, a famous technical interview question that is intended to weed out potential candidates. That question is itself derived from Fizz Buzz, a popular children's game for teaching division. https://en.wikipedia.org/wiki/Fizz_buzz

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.


import unittest

from raindrops import convert

# Tests adapted from `problem-specifications//canonical-data.json` @ v1.1.0

class RaindropsTest(unittest.TestCase):
    def test_the_sound_for_1_is_1(self):
        self.assertEqual(convert(1), "1")

    def test_the_sound_for_3_is_pling(self):
        self.assertEqual(convert(3), "Pling")

    def test_the_sound_for_5_is_plang(self):
        self.assertEqual(convert(5), "Plang")

    def test_the_sound_for_7_is_plong(self):
        self.assertEqual(convert(7), "Plong")

    def test_the_sound_for_6_is_pling_as_it_has_a_factor_3(self):
        self.assertEqual(convert(6), "Pling")

    def test_2_to_the_power_3_does_not_make_a_raindrop_sound_as_3_is_the_exponent_not_the_base(
        self.assertEqual(convert(8), "8")

    def test_the_sound_for_9_is_pling_as_it_has_a_factor_3(self):
        self.assertEqual(convert(9), "Pling")

    def test_the_sound_for_10_is_plang_as_it_has_a_factor_5(self):
        self.assertEqual(convert(10), "Plang")

    def test_the_sound_for_14_is_plong_as_it_has_a_factor_of_7(self):
        self.assertEqual(convert(14), "Plong")

    def test_the_sound_for_15_is_pling_plang_as_it_has_factors_3_and_5(self):
        self.assertEqual(convert(15), "PlingPlang")

    def test_the_sound_for_21_is_pling_plong_as_it_has_factors_3_and_7(self):
        self.assertEqual(convert(21), "PlingPlong")

    def test_the_sound_for_25_is_plang_as_it_has_a_factor_5(self):
        self.assertEqual(convert(25), "Plang")

    def test_the_sound_for_27_is_pling_as_it_has_a_factor_3(self):
        self.assertEqual(convert(27), "Pling")

    def test_the_sound_for_35_is_plang_plong_as_it_has_factors_5_and_7(self):
        self.assertEqual(convert(35), "PlangPlong")

    def test_the_sound_for_49_is_plong_as_it_has_a_factor_7(self):
        self.assertEqual(convert(49), "Plong")

    def test_the_sound_for_52_is_52(self):
        self.assertEqual(convert(52), "52")

    def test_the_sound_for_105_is_pling_plang_plong_as_it_has_factors_3_5_and_7(self):
        self.assertEqual(convert(105), "PlingPlangPlong")

    def test_the_sound_for_3125_is_plang_as_it_has_a_factor_5(self):
        self.assertEqual(convert(3125), "Plang")

if __name__ == "__main__":
def convert(number):
    raindrops = ((3, "Pling"), (5, "Plang"), (7, "Plong"))
    raindrop_result = [raindrop[1] for raindrop in raindrops if number % raindrop[0] == 0]

    return "".join(raindrop_result) or str(number)

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