exercism/python/currency-exchange/exchange.py

"""Functions for calculating steps in exchanging currency.

Python numbers documentation: https://docs.python.org/3/library/stdtypes.html#numeric-types-int-float-complex

Overview of exchanging currency when travelling: https://www.compareremit.com/money-transfer-tips/guide-to-exchanging-currency-for-overseas-travel/
"""


def exchange_money(budget, exchange_rate):
    """

    :param budget: float - amount of money you are planning to exchange.
    :param exchange_rate: float - unit value of the foreign currency.
    :return: float - exchanged value of the foreign currency you can receive.
    """

    return budget / exchange_rate


def get_change(budget, exchanging_value):
    """

    :param budget: float - amount of money you own.
    :param exchanging_value: float - amount of your money you want to exchange now.
    :return: float - amount left of your starting currency after exchanging.
    """

    return budget - exchanging_value


def get_value_of_bills(denomination, number_of_bills):
    """

    :param denomination: int - the value of a bill.
    :param number_of_bills: int - total number of bills.
    :return: int - calculated value of the bills.
    """

    return int(denomination * number_of_bills)


def get_number_of_bills(amount, denomination):
    """

    :param amount: float - the total starting value.
    :param denomination: int - the value of a single bill.
    :return: int - number of bills that can be obtained from the amount.
    """

    return amount // denomination


def get_leftover_of_bills(amount, denomination):
    """

    :param amount: float - the total starting value.
    :param denomination: int - the value of a single bill.
    :return: float - the amount that is "leftover", given the current denomination.
    """

    return amount % denomination


def exchangeable_value(budget, exchange_rate, spread, denomination):
    """

    :param budget: float - the amount of your money you are planning to exchange.
    :param exchange_rate: float - the unit value of the foreign currency.
    :param spread: int - percentage that is taken as an exchange fee.
    :param denomination: int - the value of a single bill.
    :return: int - maximum value you can get.
    """

    exchange_rate += exchange_rate * (spread / 100)

    return (
        get_number_of_bills(exchange_money(budget, exchange_rate), denomination)
        * denomination
    )