def beta_mean(alpha, beta):
    """Calculate the mean of a beta distribution.
    https://en.wikipedia.org/wiki/Beta_distribution

    :param alpha: first parameter of the beta distribution
    :type alpha: float
    :param beta: second parameter of the beta distribution
    :type beta: float

    :return: mean of the beta distribution
    :rtype: float
    """
    return alpha / (alpha + beta)