Sample an item from the pool according to the instrumental
        distribution

def _sample_item(self, **kwargs):
        """Sample an item from the pool according to the instrumental
        distribution
        """
        loc = np.random.choice(self._n_items, p = self._inst_pmf)
        weight = (1/self._n_items)/self._inst_pmf[loc]
        return loc, weight, {}