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Posted to jira@arrow.apache.org by "Sasha Krassovsky (Jira)" <ji...@apache.org> on 2021/10/18 18:30:00 UTC

[jira] [Assigned] (ARROW-13436) [Python][Doc] Clarify what should be expected if read_table is passed an empty list of columns

     [ https://issues.apache.org/jira/browse/ARROW-13436?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Sasha Krassovsky reassigned ARROW-13436:
----------------------------------------

    Assignee: Sasha Krassovsky  (was: Weston Pace)

> [Python][Doc] Clarify what should be expected if read_table is passed an empty list of columns
> ----------------------------------------------------------------------------------------------
>
>                 Key: ARROW-13436
>                 URL: https://issues.apache.org/jira/browse/ARROW-13436
>             Project: Apache Arrow
>          Issue Type: Bug
>          Components: Python
>            Reporter: Weston Pace
>            Assignee: Sasha Krassovsky
>            Priority: Major
>              Labels: good-first-issue
>
> The documentation for pyarrow.parquet.read_table states:
>  
>  * *columns* (_list_) – If not None, only these columns will be read from the file. A column name may be a prefix of a nested field, e.g. ‘a’ will select ‘a.b’, ‘a.c’, and ‘a.d.e’.
>  
> It is not clear what should be the expected result if columns is an empty list.  In pyarrow 3.0 this read in all columns (as long as use_legacy_dataset=False).  In pyarrow 4.0 this doesn't read in any columns.  I think this behavior (not reading in any columns) is the correct behavior (since None can be used for all columns) but we should clarify that in the docs.



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