[jira] [Closed] (ARROW-6486) [Python] Allow subclassing & monkey-patching of Table

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

     [ https://issues.apache.org/jira/browse/ARROW-6486?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Wes McKinney closed ARROW-6486.
-------------------------------
    Resolution: Won't Fix

> [Python] Allow subclassing & monkey-patching of Table
> -----------------------------------------------------
>
>                 Key: ARROW-6486
>                 URL: https://issues.apache.org/jira/browse/ARROW-6486
>             Project: Apache Arrow
>          Issue Type: Improvement
>          Components: Python
>            Reporter: ARF
>            Priority: Major
>              Labels: pull-request-available
>          Time Spent: 1h 50m
>  Remaining Estimate: 0h
>
> Currently, many classes in {{pyarrow}} behave strangely to the Python user: they are neither subclassable not monkey-patchable.
>  
> {{>>> import pyarrow as pa}}
>  {{>>> class MyTable(pa.Table):}}
>  {{... pass}}
>  {{...}}
>  {{>>> table = MyTable.from_arrays([], [])}}
>  {{>>> type(table)}}
>  {{<class 'pyarrow.lib.Table'>}}
> The factory method did not return an instance of our subclass...
> Never mind, let's monkey-patch {{Table}}:
> {{>>> pa.TableOriginal = pa.Table}}
>  {{>>> pa.Table = MyTable}}
>  {{>>> table = pa.Table.from_arrays([], [])}}
>  {{>>> type(table)}}
>  {{<class 'pyarrow.lib.Table'>}}
>  
> OK, that did not work either.
> Let's be sneaky:
> {{>>> table.__class__ = MyTable}}
>  {{Traceback (most recent call last):}}
>  \{{ File "<stdin>", line 1, in <module>}}
>  {{TypeError: __class__ assignment only supported for heap types or ModuleType subclasses}}
>  {{>>>}}
>  
> There is currently no way to modify or extend the behaviour of a {{Table}} instance. Users can use only what {{pyarrow}} provides out of the box. - This is likely to be a source of frustration for many python users.
>  
> The attached PR remedies this for the {{Table}} class:
> {{>>> import pyarrow as pa}}
>  {{>>> class MyTable(pa.Table):}}
>  {{... pass}}
>  {{...}}
>  {{>>> table = MyTable.from_arrays([], [])}}
>  {{>>> type(table)}}
>  {{<class '__main__.MyTable'>}}
>  {{>>>}}
>  {{>>> pa.TableOriginal = pa.Table}}
>  {{>>> pa.Table = MyTable}}
>  {{>>> table = pa.Table.from_arrays([], [])}}
>  {{>>> type(table)}}
>  {{<class '__main__.MyTable'>}}
>  {{>>>}}
>  
> Ideally, these modifications would be extended to the other cython-defined classes of {{pyarrow}}, but given that Table is likely to be the interface that most users begin their interaction with, I thought this would be a good start.
> Keeping the changes limited to a single class should also keep merge conflicts manageable.



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