[jira] [Commented] (ARROW-6642) [Python] chained access of ParquetDataset's metadata segfaults

["Wes McKinney (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/ARROW-6642?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16934491#comment-16934491 ] 

Wes McKinney commented on ARROW-6642:
-------------------------------------

Ah, we need to add "base" Python references to the objects returned by {{row_group}} and {{column}} so the {{FileMetaData}} object isn't garbage collected

> [Python] chained access of ParquetDataset's metadata segfaults
> --------------------------------------------------------------
>
>                 Key: ARROW-6642
>                 URL: https://issues.apache.org/jira/browse/ARROW-6642
>             Project: Apache Arrow
>          Issue Type: Bug
>          Components: Python
>            Reporter: Joris Van den Bossche
>            Priority: Major
>              Labels: parquet
>             Fix For: 0.15.0
>
>
> Creating and reading a parquet dataset:
> {code}
> table = pa.table({'a': [1, 2, 3]})
> import pyarrow.parquet as pq
> pq.write_table(table, '__test_statistics_segfault.parquet')
> dataset = pq.ParquetDataset('__test_statistics_segfault.parquet')
> dataset_piece = dataset.pieces[0]
> {code}
> If you access the metadata and a column's statistics in steps, this works fine:
> {code}
> meta = dataset_piece.get_metadata()
> row = meta.row_group(0)
> col = row.column(0)
> {code}
> but doing it chained in one step, this segfaults:
> {code}
> dataset_piece.get_metadata().row_group(0).column(0)
> {code}
> {{dataset_piece.get_metadata().row_group(0)}} still works, but additionally with {{.column(0)}} then it segfaults. 



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