def namedb_history_extract( history_rows ):
    """
    Given the rows of history for a name, collapse
    them into a history dictionary.
    Return a dict of:
    {
        block_id: [
            { ... historical copy ...
             txid:
             vtxindex:
             op:
             opcode: 
            }, ...
        ],
        ...
    }
    """

    history = {}
    for history_row in history_rows:

        block_id = history_row['block_id']
        data_json = history_row['history_data']
        hist = json.loads( data_json )
        
        hist['opcode'] = op_get_opcode_name( hist['op'] )
        hist = op_decanonicalize(hist['opcode'], hist)

        if history.has_key( block_id ):
            history[ block_id ].append( hist )
        else:
            history[ block_id ] = [ hist ]

    return history