def sum_multiples(limit):
    """Sums all multiples of 3 and 5 under `limit`

    Args:
        limit (int): The limit that the sums will be calculated up to

    Returns:
        int : The sum of all multiples of 3 and 5 up to `limit`
    """
    return sum(x for x in range(limit) if x % 3 == 0 or x % 5 == 0)