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rootulp's solution

to Clock in the Python Track

Published at Jul 13 2018 · 2 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.

Implement a clock that handles times without dates.

You should be able to add and subtract minutes to it.

Two clocks that represent the same time should be equal to each other.

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 clock_test.py
  • Python 3.4+: pytest clock_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 clock_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/clock 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 the help page.


Pairing session with Erin Drummond https://twitter.com/ebdrummond

Submitting Incomplete Solutions

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


import unittest

from clock import Clock

# Tests adapted from `problem-specifications//canonical-data.json` @ v2.2.1

class ClockTest(unittest.TestCase):
    # Test creating a new clock with an initial time.
    def test_on_the_hour(self):
        self.assertEqual(str(Clock(8, 0)), '08:00')

    def test_past_the_hour(self):
        self.assertEqual(str(Clock(11, 9)), '11:09')

    def test_midnight_is_zero_hours(self):
        self.assertEqual(str(Clock(24, 0)), '00:00')

    def test_hour_rolls_over(self):
        self.assertEqual(str(Clock(25, 0)), '01:00')

    def test_hour_rolls_over_continuously(self):
        self.assertEqual(str(Clock(100, 0)), '04:00')

    def test_sixty_minutes_is_next_hour(self):
        self.assertEqual(str(Clock(1, 60)), '02:00')

    def test_minutes_roll_over(self):
        self.assertEqual(str(Clock(0, 160)), '02:40')

    def test_minutes_roll_over_continuously(self):
        self.assertEqual(str(Clock(0, 1723)), '04:43')

    def test_hour_and_minutes_roll_over(self):
        self.assertEqual(str(Clock(25, 160)), '03:40')

    def test_hour_and_minutes_roll_over_continuously(self):
        self.assertEqual(str(Clock(201, 3001)), '11:01')

    def test_hour_and_minutes_roll_over_to_exactly_midnight(self):
        self.assertEqual(str(Clock(72, 8640)), '00:00')

    def test_negative_hour(self):
        self.assertEqual(str(Clock(-1, 15)), '23:15')

    def test_negative_hour_rolls_over(self):
        self.assertEqual(str(Clock(-25, 0)), '23:00')

    def test_negative_hour_rolls_over_continuously(self):
        self.assertEqual(str(Clock(-91, 0)), '05:00')

    def test_negative_minutes(self):
        self.assertEqual(str(Clock(1, -40)), '00:20')

    def test_negative_minutes_roll_over(self):
        self.assertEqual(str(Clock(1, -160)), '22:20')

    def test_negative_minutes_roll_over_continuously(self):
        self.assertEqual(str(Clock(1, -4820)), '16:40')

    def test_negative_hour_and_minutes_both_roll_over(self):
        self.assertEqual(str(Clock(-25, -160)), '20:20')

    def test_negative_hour_and_minutes_both_roll_over_continuously(self):
        self.assertEqual(str(Clock(-121, -5810)), '22:10')

    # Test adding and subtracting minutes.
    def test_add_minutes(self):
        self.assertEqual(str(Clock(10, 0) + 3), '10:03')

    def test_add_no_minutes(self):
        self.assertEqual(str(Clock(6, 41) + 0), '06:41')

    def test_add_to_next_hour(self):
        self.assertEqual(str(Clock(0, 45) + 40), '01:25')

    def test_add_more_than_one_hour(self):
        self.assertEqual(str(Clock(10, 0) + 61), '11:01')

    def test_add_more_than_two_hours_with_carry(self):
        self.assertEqual(str(Clock(0, 45) + 160), '03:25')

    def test_add_across_midnight(self):
        self.assertEqual(str(Clock(23, 59) + 2), '00:01')

    def test_add_more_than_one_day(self):
        self.assertEqual(str(Clock(5, 32) + 1500), '06:32')

    def test_add_more_than_two_days(self):
        self.assertEqual(str(Clock(1, 1) + 3500), '11:21')

    def test_subtract_minutes(self):
        self.assertEqual(str(Clock(10, 3) - 3), '10:00')

    def test_subtract_to_previous_hour(self):
        self.assertEqual(str(Clock(10, 3) - 30), '09:33')

    def test_subtract_more_than_an_hour(self):
        self.assertEqual(str(Clock(10, 3) - 70), '08:53')

    def test_subtract_across_midnight(self):
        self.assertEqual(str(Clock(0, 3) - 4), '23:59')

    def test_subtract_more_than_two_hours(self):
        self.assertEqual(str(Clock(0, 0) - 160), '21:20')

    def test_subtract_more_than_two_hours_with_borrow(self):
        self.assertEqual(str(Clock(6, 15) - 160), '03:35')

    def test_subtract_more_than_one_day(self):
        self.assertEqual(str(Clock(5, 32) - 1500), '04:32')

    def test_subtract_more_than_two_days(self):
        self.assertEqual(str(Clock(2, 20) - 3000), '00:20')

    # Construct two separate clocks, set times, test if they are equal.
    def test_clocks_with_same_time(self):
        self.assertEqual(Clock(15, 37), Clock(15, 37))

    def test_clocks_a_minute_apart(self):
        self.assertNotEqual(Clock(15, 36), Clock(15, 37))

    def test_clocks_an_hour_apart(self):
        self.assertNotEqual(Clock(14, 37), Clock(15, 37))

    def test_clocks_with_hour_overflow(self):
        self.assertEqual(Clock(10, 37), Clock(34, 37))

    def test_clocks_with_hour_overflow_by_several_days(self):
        self.assertEqual(Clock(3, 11), Clock(99, 11))

    def test_clocks_with_negative_hour(self):
        self.assertEqual(Clock(22, 40), Clock(-2, 40))

    def test_clocks_with_negative_hour_that_wraps(self):
        self.assertEqual(Clock(17, 3), Clock(-31, 3))

    def test_clocks_with_negative_hour_that_wraps_multiple_times(self):
        self.assertEqual(Clock(13, 49), Clock(-83, 49))

    def test_clocks_with_minute_overflow(self):
        self.assertEqual(Clock(0, 1), Clock(0, 1441))

    def test_clocks_with_minute_overflow_by_several_days(self):
        self.assertEqual(Clock(2, 2), Clock(2, 4322))

    def test_clocks_with_negative_minute(self):
        self.assertEqual(Clock(2, 40), Clock(3, -20))

    def test_clocks_with_negative_minute_that_wraps(self):
        self.assertEqual(Clock(4, 10), Clock(5, -1490))

    def test_clocks_with_negative_minute_that_wraps_multiple_times(self):
        self.assertEqual(Clock(6, 15), Clock(6, -4305))

    def test_clocks_with_negative_hours_and_minutes(self):
        self.assertEqual(Clock(7, 32), Clock(-12, -268))

    def test_clocks_with_negative_hours_and_minutes_that_wrap(self):
        self.assertEqual(Clock(18, 7), Clock(-54, -11513))

if __name__ == '__main__':
class Clock:
    def __init__(self, hours, mins):
        self.hours = hours
        self.mins = mins

    def __eq__(self, other):
        return (self.hours == other.hours and
                self.mins == other.mins)

    def __str__(self):
        return (self.format_hours() + ':' +

    def add(self, additional_mins):
        self.mins += additional_mins
        return self

    def fixup(self):

    def fixup_hours(self):
        self.hours = self.hours % 24

    def fixup_mins(self):
        self.hours += self.mins / 60
        self.mins = self.mins % 60

    def format_hours(self):
        return str(self.hours).zfill(2)

    def format_mins(self):
        return str(self.mins).zfill(2)

Community comments

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

Fails 42 tests (out of 50) on Python 3

Avatar of rootulp

It seems to pass all tests on Python 2.7.12 I'm guessing there is a syntax issue in Python 3

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