Раcсчет аннуительного платежа

annuity_payment.py

def calculate_monthly_payment(
    *,
    loan: float | int | str | Decimal,
    annual_interest_rate: float | str | Decimal,
    years: int | None = None,
    months: int | None = None,
):
    """
    Calculates the annuity monthly mortgage payment

    An example of a loan in the amount of 9M at 11% per annum for 15 years:
    >>> calculate_monthly_payment(loan=9_000_000, annual_interest_rate="0.11", years=15)
    """
    s = Decimal(loan)
    p = Decimal(annual_interest_rate)
    n = 12 * years if years else months
    return s * p / 12 * (1 + p / 12) ** n / ((1 + p / 12) ** n - 1)