Get the retrieved block information.
        Return [(height, [txs])] on success, ordered on height
        Raise if not finished downloading

def get_block_info(self):
        """
        Get the retrieved block information.
        Return [(height, [txs])] on success, ordered on height
        Raise if not finished downloading
        """
        if not self.finished:
            raise Exception("Not finished downloading")

        ret = []
        for (block_hash, block_data) in self.block_info.items():
            ret.append( (block_data['height'], block_data['txns']) )

        return ret