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# la5tway's solution

## to Leap in the Python Track

Published at Jul 10 2020 · 0 comments
Instructions
Test suite
Solution

#### Note:

This exercise has changed since this solution was written.

Given a year, report if it is a leap year.

The tricky thing here is that a leap year in the Gregorian calendar occurs:

``````on every year that is evenly divisible by 4
except every year that is evenly divisible by 100
unless the year is also evenly divisible by 400
``````

For example, 1997 is not a leap year, but 1996 is. 1900 is not a leap year, but 2000 is.

## Notes

Though our exercise adopts some very simple rules, there is more to learn!

For a delightful, four minute explanation of the whole leap year phenomenon, go watch this youtube video.

## 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 leap_test.py`

Alternatively, you can tell Python to run the pytest module: `python -m pytest leap_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/leap` 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.

## Source

JavaRanch Cattle Drive, exercise 3 http://www.javaranch.com/leap.jsp

## Submitting Incomplete Solutions

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

### leap_test.py

``````import unittest

from leap import leap_year

# Tests adapted from `problem-specifications//canonical-data.json` @ v1.6.0

class LeapTest(unittest.TestCase):
def test_year_not_divisible_by_4_in_common_year(self):
self.assertIs(leap_year(2015), False)

def test_year_divisible_by_2_not_divisible_by_4_in_common_year(self):
self.assertIs(leap_year(1970), False)

def test_year_divisible_by_4_not_divisible_by_100_in_leap_year(self):
self.assertIs(leap_year(1996), True)

def test_year_divisible_by_4_and_5_is_still_a_leap_year(self):
self.assertIs(leap_year(1960), True)

def test_year_divisible_by_100_not_divisible_by_400_in_common_year(self):
self.assertIs(leap_year(2100), False)

def test_year_divisible_by_100_but_not_by_3_is_still_not_a_leap_year(self):
self.assertIs(leap_year(1900), False)

def test_year_divisible_by_400_in_leap_year(self):
self.assertIs(leap_year(2000), True)

def test_year_divisible_by_400_but_not_by_125_is_still_a_leap_year(self):
self.assertIs(leap_year(2400), True)

def test_year_divisible_by_200_not_divisible_by_400_in_common_year(self):
self.assertIs(leap_year(1800), False)

if __name__ == "__main__":
unittest.main()``````
``````def leap_year(year: int) -> bool:
return (year % 4 == 0 and year % 100 != 0) or year % 400 == 0``````