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to Sum Of Multiples in the Python Track

Published at Jul 13 2018 · 0 comments
Test suite


This solution was written on an old version of Exercism. The tests below might not correspond to the solution code, and the exercise may have changed since this code was written.

Given a number, find the sum of all the unique multiples of particular numbers up to but not including that number.

If we list all the natural numbers below 20 that are multiples of 3 or 5, we get 3, 5, 6, 9, 10, 12, 15, and 18.

The sum of these multiples is 78.

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 sum_of_multiples_test.py
  • Python 3.4+: pytest sum_of_multiples_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 sum_of_multiples_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/sum-of-multiples 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 Problem 1 at Project Euler http://projecteuler.net/problem=1

Submitting Incomplete Solutions

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


You can make the following assumptions about the inputs to the
'sum_of_multiples' function:
    * All input numbers are non-negative 'int's, i.e. natural numbers
      including zero.
    * A list of factors must be given, and its elements are unique
      and sorted in ascending order.

import unittest

from sum_of_multiples import sum_of_multiples

# Tests adapted from `problem-specifications//canonical-data.json` @ v1.5.0

class SumOfMultiplesTest(unittest.TestCase):
    def test_multiples_with_no_factors_in_limit(self):
        self.assertEqual(sum_of_multiples(1, [3, 5]), 0)

    def test_multiples_of_one_factor_within_limit(self):
        self.assertEqual(sum_of_multiples(4, [3, 5]), 3)

    def test_various_multiples_in_limit(self):
        self.assertEqual(sum_of_multiples(7, [3]), 9)

    def test_various_factors_with_multiples_in_limit(self):
        self.assertEqual(sum_of_multiples(10, [3, 5]), 23)

    def test_multiples_counted_only_once(self):
        self.assertEqual(sum_of_multiples(100, [3, 5]), 2318)

    def test_multiples_with_large_limit(self):
        self.assertEqual(sum_of_multiples(1000, [3, 5]), 233168)

    def test_multiples_with_three_factors(self):
        self.assertEqual(sum_of_multiples(20, [7, 13, 17]), 51)

    def test_multiples_with_factors_not_prime(self):
        self.assertEqual(sum_of_multiples(15, [4, 6]), 30)

    def test_multiples_with_factors_prime_and_not(self):
        self.assertEqual(sum_of_multiples(150, [5, 6, 8]), 4419)

    def test_multiples_with_similar_factors(self):
        self.assertEqual(sum_of_multiples(51, [5, 25]), 275)

    def test_multiples_with_large_factors(self):
        self.assertEqual(sum_of_multiples(10000, [43, 47]), 2203160)

    def test_multiples_of_one_will_be_all(self):
        self.assertEqual(sum_of_multiples(100, [1]), 4950)

    def test_multiples_of_an_empty_list(self):
        self.assertEqual(sum_of_multiples(10000, []), 0)

    def test_multiples_of_zero_will_be_none(self):
        self.assertEqual(sum_of_multiples(1, [0]), 0)

    def test_multiples_with_a_zero_factor(self):
        self.assertEqual(sum_of_multiples(4, [0, 3]), 3)

    def test_multiples_of_several_factors(self):
                         [2, 3, 5, 7, 11]), 39614537)

if __name__ == '__main__':
from itertools import chain

def sum_of_multiples(limit, factors):
    return sum(all_multiples(limit, factors))

def all_multiples(limit, factors):
    multiples = [get_multiples(limit, factor) for factor in factors]
    return set(list(chain(*multiples)))  # remove duplicates

def get_multiples(limit, factor):
    if factor == 0:
        return []
    return [multiple for multiple in range(limit) if multiple % factor == 0]

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