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https://issues.apache.org/jira/browse/ARROW-5610?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16882036#comment-16882036
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Antoine Pitrou commented on ARROW-5610:
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> You want to transfer a table containing a column of that type to and from
> Python. Right now, you can read that data from Python, but you can't create a
> table with that type
I'm curious, which error do you get when trying to do so?
> You also can't deserialize the metadata written by Java or write metadata
> that Java can read, as it's not in pickle format.
I think you're mixing up extension types defined *in Python* and extension
types defined in other languages. I don't remember if the Python
BaseExtensionType class lets you access the raw unserialized metadata. But if
it doesn't, it's just a single property to add to that class ;)
As for _writing_ arbitrary metadata in the name of an existing ExtensionType,
C++ doesn't allow you to do that IIRC, and Python just wraps the C++ class. So
when you're complaining about a missing facility in Python, it seems you're
actually complaining about a missing facility in C++.
> [Python] Define extension type API in Python to "receive" or "send" a foreign
> extension type
> --------------------------------------------------------------------------------------------
>
> Key: ARROW-5610
> URL: https://issues.apache.org/jira/browse/ARROW-5610
> Project: Apache Arrow
> Issue Type: Improvement
> Components: Python
> Reporter: Wes McKinney
> Priority: Major
> Fix For: 1.0.0
>
>
> In work in ARROW-840, a static {{arrow.py_extension_type}} name is used.
> There will be cases where an extension type is coming from another
> programming language (e.g. Java), so it would be useful to be able to "plug
> in" a Python extension type subclass that will be used to deserialize the
> extension type coming over the wire. This has some different API requirements
> since the serialized representation of the type will not have knowledge of
> Python pickling, etc.
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