import numpy as np

class BernoulliDistribution():
    def __init__(self, p = 0.5):
        self._p = p
    def mean(self):
        return self._p
    def var(self):
        p = self._p
        return p * (1 - p)
    def std(self):
        return np.sqrt(self.var())

B1 = BernoulliDistribution() # (p = 0.5)

B1.mean()

0.5

B2 = BernoulliDistribution(p = 0.77)
B2.mean()

0.77