Exercism v3 launches on Sept 1st 2021. Learn more! ๐Ÿš€๐Ÿš€๐Ÿš€
Avatar of rootulp

rootulp's solution

to Raindrops in the Python Track

Published at Dec 28 2018 · 0 comments
Test suite


This exercise has changed since this solution was written.

Convert a number to a string, the contents of which depend on the number's factors.

  • If the number has 3 as a factor, output 'Pling'.
  • If the number has 5 as a factor, output 'Plang'.
  • If the number has 7 as a factor, output 'Plong'.
  • If the number does not have 3, 5, or 7 as a factor, just pass the number's digits straight through.


  • 28's factors are 1, 2, 4, 7, 14, 28.
    • In raindrop-speak, this would be a simple "Plong".
  • 30's factors are 1, 2, 3, 5, 6, 10, 15, 30.
    • In raindrop-speak, this would be a "PlingPlang".
  • 34 has four factors: 1, 2, 17, and 34.
    • In raindrop-speak, this 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 the appropriate command below (why they are different):

  • Python 2.7: py.test raindrops_test.py
  • Python 3.4+: pytest raindrops_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 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 a famous interview question intended to weed out potential candidates. http://jumpstartlab.com

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 raindrops

# 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(raindrops(1), "1")

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

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

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

    def test_the_sound_for_6_is_pling(self):
        self.assertEqual(raindrops(6), "Pling")

    def test_2_to_the_power_3_does_not_make_sound(self):
        self.assertEqual(raindrops(8), "8")

    def test_the_sound_for_9_is_pling(self):
        self.assertEqual(raindrops(9), "Pling")

    def test_the_sound_for_10_is_plang(self):
        self.assertEqual(raindrops(10), "Plang")

    def test_the_sound_for_14_is_plong(self):
        self.assertEqual(raindrops(14), "Plong")

    def test_the_sound_for_15_is_plingplang(self):
        self.assertEqual(raindrops(15), "PlingPlang")

    def test_the_sound_for_21_is_plingplong(self):
        self.assertEqual(raindrops(21), "PlingPlong")

    def test_the_sound_for_25_is_plang(self):
        self.assertEqual(raindrops(25), "Plang")

    def test_the_sound_for_27_is_pling(self):
        self.assertEqual(raindrops(27), "Pling")

    def test_the_sound_for_35_is_plangplong(self):
        self.assertEqual(raindrops(35), "PlangPlong")

    def test_the_sound_for_49_is_plong(self):
        self.assertEqual(raindrops(49), "Plong")

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

    def test_the_sound_for_105_is_plingplangplong(self):
        self.assertEqual(raindrops(105), "PlingPlangPlong")

    def test_the_sound_for_12121_is_12121(self):
        self.assertEqual(raindrops(12121), "12121")

if __name__ == '__main__':
def raindrops(number):
    message = convert_to_message(number)
    return message if message else "{}".format(number)

def convert_to_message(number):
    return f"{'Pling' if is_three_a_factor(number) else ''}" \
           f"{'Plang' if is_five_a_factor(number) else ''}" \
           f"{'Plong' if is_seven_a_factor(number) else ''}"

def is_three_a_factor(number):
    return is_factor(number, 3)

def is_five_a_factor(number):
    return is_factor(number, 5)

def is_seven_a_factor(number):
    return is_factor(number, 7)

def is_factor(number, potentialFactor):
    return number % potentialFactor == 0

Community comments

Find this solution interesting? Ask the author a question to learn more.

What can you learn from this solution?

A huge amount can be learned from reading other peopleโ€™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.

  • What compromises have been made?
  • Are there new concepts here that you could read more about to improve your understanding?