def entropy(self, base = 2):
        """Compute the entropy of the distribution"""
        entropy = 0
        if not base and self.base: base = self.base
        for type in self._dist:
            if not base:
                entropy += self._dist[type] * -math.log(self._dist[type])
            else:
                entropy += self._dist[type] * -math.log(self._dist[type], base)
        return entropy
Compute the entropy of the distribution