def handle_split(self, asset, ratio):
        """
        Update the position by the split ratio, and return the resulting
        fractional share that will be converted into cash.

        Returns the unused cash.
        """
        if self.asset != asset:
            raise Exception("updating split with the wrong asset!")

        # adjust the # of shares by the ratio
        # (if we had 100 shares, and the ratio is 3,
        #  we now have 33 shares)
        # (old_share_count / ratio = new_share_count)
        # (old_price * ratio = new_price)

        # e.g., 33.333
        raw_share_count = self.amount / float(ratio)

        # e.g., 33
        full_share_count = np.floor(raw_share_count)

        # e.g., 0.333
        fractional_share_count = raw_share_count - full_share_count

        # adjust the cost basis to the nearest cent, e.g., 60.0
        new_cost_basis = round(self.cost_basis * ratio, 2)

        self.cost_basis = new_cost_basis
        self.amount = full_share_count

        return_cash = round(float(fractional_share_count * new_cost_basis), 2)

        log.info("after split: " + str(self))
        log.info("returning cash: " + str(return_cash))

        # return the leftover cash, which will be converted into cash
        # (rounded to the nearest cent)
        return return_cash
Update the position by the split ratio, and return the resulting
        fractional share that will be converted into cash.

        Returns the unused cash.