[jira] [Commented] (ARROW-16254) [Python] Scalar constructors should be callable

["Antoine Pitrou (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/ARROW-16254?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17524932#comment-17524932 ] 

Antoine Pitrou commented on ARROW-16254:
----------------------------------------

cc [~alenkaf] [~raulcd]

> [Python] Scalar constructors should be callable
> -----------------------------------------------
>
>                 Key: ARROW-16254
>                 URL: https://issues.apache.org/jira/browse/ARROW-16254
>             Project: Apache Arrow
>          Issue Type: Improvement
>          Components: Python
>            Reporter: Antoine Pitrou
>            Priority: Major
>             Fix For: 9.0.0
>
>
> Currently, to create a Scalar instance you must call the {{pa.scalar}} factory function. This works fine for the simplest types, but not for more elaborate ones.
> For example, in C++ it is trivial to create a {{ListScalar}} from the embedded {{std::shared_ptr<Array>}}. But not in Python:
> {code:python}
> >>> arr = pa.array(["abc", "def", "ghi"])
> >>> pa.ListScalar(arr)
> Traceback (most recent call last):
>   Input In [7] in <cell line: 1>
>     pa.ListScalar(arr)
> TypeError: __init__() takes exactly 0 positional arguments (1 given)
> {code}
> There is a clumsy workaround that creates an intermediate {{ListArray}} with trivial offsets:
> {code:python}
> >>> list_arr = pa.ListArray.from_arrays([0, len(arr)], arr)
> >>> list_arr[0]
> <pyarrow.ListScalar: ['abc', 'def', 'ghi']>
> {code}



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