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https://issues.apache.org/jira/browse/ARROW-2307?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16399684#comment-16399684
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ASF GitHub Bot commented on ARROW-2307:
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wesm commented on issue #1747: ARROW-2307: [Python] Allow reading record batch
streams with zero record batches
URL: https://github.com/apache/arrow/pull/1747#issuecomment-373223120
+1. Appveyor build looking good:
https://ci.appveyor.com/project/wesm/arrow/build/1.0.1776
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> [Python] Unable to read arrow stream containing 0 record batches
> ----------------------------------------------------------------
>
> Key: ARROW-2307
> URL: https://issues.apache.org/jira/browse/ARROW-2307
> Project: Apache Arrow
> Issue Type: Bug
> Components: Python
> Affects Versions: 0.8.0
> Reporter: Benjamin Duffield
> Assignee: Wes McKinney
> Priority: Major
> Labels: pull-request-available
>
> Using java arrow I'm creating an arrow stream, using the stream writer.
>
> Sometimes I don't have anything to serialize, and so I don't write any record
> batches. My arrow stream thus consists of just a schema message.
> {code:java}
> <SCHEMA>
> <EOS [optional]: int32>
> {code}
> I am able to deserialize this arrow stream correctly using the java stream
> reader, but when reading it with python I instead hit an error
> {code}
> import pyarrow as pa
> # ...
> reader = pa.open_stream(stream)
> df = reader.read_all().to_pandas()
> {code}
> produces
> {code}
> File "ipc.pxi", line 307, in pyarrow.lib._RecordBatchReader.read_all
> File "error.pxi", line 77, in pyarrow.lib.check_status
> ArrowInvalid: Must pass at least one record batch
> {code}
> i.e. we're hitting the check in
> https://github.com/apache/arrow/blob/apache-arrow-0.8.0/cpp/src/arrow/table.cc#L284
> The workaround we're currently using is to always ensure we serialize at
> least one record batch, even if it's empty. However, I think it would be nice
> to either support a stream without record batches or explicitly disallow this
> and then match behaviour in java.
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