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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def Var(self, mu=None):
 """Computes the variance of a PMF. Args: mu: the point around which the variance is computed; if omitted, computes the mean Returns: float variance """

        if mu is None:
            mu = self.Mean()

        var = 0.0
        for x, p in self.d.iteritems():
            var += p * (x - mu) ** 2
        return var