Trying out a fizzbuzz game

fizzbuzz.py

import sys


def get_fizzbuzz(start=1):
    if start < 1:
        raise ValueError('Cannot start below 1')
    start -= 1
    while True:
        start += 1
        if not (start % 3) and (start % 5):
            yield 'Fizz'
        elif not (start % 5) and (start % 3):
            yield 'Buzz'
        elif not (start % 5 + start % 3):
            yield 'FizzBuzz'
        else:
            yield start


if __name__ == '__main__':
    if len(sys.argv) > 1:
        start = int(sys.argv[1])
    else:
        start = 1
    if len(sys.argv) > 2:
        end = int(sys.argv[2])
    else:
        end = 100
    if not isinstance(start, int):
        raise RuntimeError('You must use an integer as a starting value if you specify one (got {})'.format(start))
    if not isinstance(end, int):
        raise RuntimeError('You must use an integer as a count if you specify one (got {})'.format(end))
    g = get_fizzbuzz(start=start)
    for i in range(end - start):
        print(next(g))