Python の doctest を試してみる。

fizzbuzz.py

import itertools
from collections.abc import Iterator


def fizzbuzz(n: int) -> Iterator[int | str]:
    '''
    Return the fizzbuzz of n, an exact integer >= 0.

    >>> from fizzbuzz import fizzbuzz
    >>> [i for i in fizzbuzz(15)]
    [1, 2, 'Fizz', 4, 'Buzz', 'Fizz', 7, 8, 'Fizz', 'Buzz', 11, 'Fizz', 13, 14, 'FizzBuzz']
    >>> from collections.abc import Iterator
    >>> isinstance(fizzbuzz(15), Iterator)
    True
    >>> fizzbuzz(15.0)
    Traceback (most recent call last):
        ...
    ValueError: n must be an integer
    >>> fizzbuzz(-1)
    Traceback (most recent call last):
        ...
    ValueError: n must be >= 0
    '''

    if not isinstance(n, int):
        raise ValueError('n must be an integer')
    if not n >= 0:
        raise ValueError('n must be >= 0')

    numbers = itertools.count(1)
    fizzes = itertools.cycle((*itertools.repeat('', 3 - 1), 'Fizz'))
    buzzes = itertools.cycle((*itertools.repeat('', 5 - 1), 'Buzz'))
    fizzbuzz_generator = (f'{fizz}{buzz}' or n for n,
                          fizz, buzz in zip(numbers, fizzes, buzzes))

    return itertools.islice(fizzbuzz_generator, n)


if __name__ == '__main__':
    import doctest
    doctest.testmod()

stdout

$ python fizzbuzz.py -v
Trying:
    from fizzbuzz import fizzbuzz
Expecting nothing
ok
Trying:
    [i for i in fizzbuzz(15)]
Expecting:
    [1, 2, 'Fizz', 4, 'Buzz', 'Fizz', 7, 8, 'Fizz', 'Buzz', 11, 'Fizz', 13, 14, 'FizzBuzz']
ok
Trying:
    from collections.abc import Iterator
Expecting nothing
ok
Trying:
    isinstance(fizzbuzz(15), Iterator)
Expecting:
    True
ok
Trying:
    fizzbuzz(15.0)
Expecting:
    Traceback (most recent call last):
        ...
    ValueError: n must be an integer
ok
Trying:
    fizzbuzz(-1)
Expecting:
    Traceback (most recent call last):
        ...
    ValueError: n must be >= 0
ok
1 items had no tests:
    __main__
1 items passed all tests:
   6 tests in __main__.fizzbuzz
6 tests in 2 items.
6 passed and 0 failed.
Test passed.

References

• https://docs.python.org/ja/3/library/doctest.html
• https://docs.python.org/ja/3/glossary.html#term-docstring
• 怠惰な FizzBuzz を作ってみた (Python 版) - Qiita