"""
Demonstrates how to use optional parameters in functions
"""


def optional(val, multiplier=1, adder=0):
    """
    Multiply val by multiplier and add adder
    :param val: (int) the base value
    :param multiplier: (int) how much to multiply the base value
    :param adder: (int) how much to add to the product of val and multiplier
    :return: (int) val*multiplier + adder
    """

    return val*multiplier + adder


def list_of_nums(start, stop, step=1):
    """
    Returns a list of numbers [start, start+step, start+step*2, ..., stop)
    :param start: (int) the first number in the list (inclusive)
    :param stop: (int) the last number in the list (exclusive)
    :param step: (int) the difference between two consecutive numbers in the list
    :return: (list of ints) a list of numbers [start, start+step, start+step*2, ..., stop)
    """
    i = start
    r = []

    while i < stop:
        r.append(i)
        i += step

    return r