Correct formula in class Gaussian

[Shwetago]

While calculating u in pdf function, it should be sigma square

class Gaussian:
    "Model univariate Gaussian"
    def __init__(self, mu, sigma):
        #mean and standard deviation
        self.mu = mu
        self.sigma = sigma

    #probability density function
    def pdf(self, datum):
        "Probability of a data point given the current parameters"
        u = (datum - self.mu) / abs(self.sigma)
        y = (1 / (sqrt(2 * pi) * abs(self.sigma))) * exp(-u * u / 2)
        return y
    #printing model values
    def __repr__(self):
        return 'Gaussian({0:4.6}, {1:4.6})'.format(self.mu, self.sigma)