voltage_divider 2

def solve(Vin=None, Vout=None, R1=None, R2=None, RL=None):
    """
    Calculation of a voltage divider with load.

    >>> solve(24, 10, 500, RL=390)
    4239.130434782609

    Reference: http://www.sengpielaudio.com/Rechner-spannungsteiler.htm
    """
    missing = [key for key, value in locals().items() if value is None]
    if len(missing) != 1:
        raise TypeError("One Value must be None")
    missing = missing[0]
    if missing == "Vin":
        return Vout * (R1 * R2 + R1 * RL + R2 * RL) / (R2 * RL)
    elif missing == "Vout":
        return Vin * R2 * RL / (R1 * R2 + R1 * RL + R2 * RL)
    elif missing == "R1":
        return ((Vin - Vout) / Vout) * R2 * RL / (R2 + RL)
    elif missing == "R2":
        return Vout * R1 * RL / (RL * Vin - Vout * R1 - Vout * RL)
    elif missing == "RL":
        return Vout * R1 * R2 / (R2 * Vin - Vout * R1 - Vout * R2)