average 0.6.0

def online(data):
    n = 0.
    mean = 0.
    M2 = 0.
    M3 = 0.
    M4 = 0.

    for x in data:
        n1 = n
        n = n + 1
        delta = x - mean
        delta_n = delta / n
        delta_n2 = delta_n * delta_n
        term1 = delta * delta_n * n1
        mean = mean + delta_n
        M4 = M4 + term1 * delta_n2 * (n*n - 3*n + 3) + 6 * delta_n2 * M2 - 4 * delta_n * M3
        M3 = M3 + term1 * delta_n * (n - 2) - 3 * delta_n * M2
        M2 = M2 + term1

    skewness = n**0.5 * M3 / (M2**(3./2))
    kurtosis = (n*M4) / (M2*M2) - 3
    print "skewness:", skewness
    print "kurtosis:", kurtosis

if __name__ == '__main__':
    data = range(1, 6) + [1]
    online(data)