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https://issues.apache.org/jira/browse/ARROW-5169?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Joris Van den Bossche reassigned ARROW-5169:
--------------------------------------------
Assignee: Joris Van den Bossche
> [Python] non-nullable fields are converted to nullable in
> {{Table.from_pandas}}
> -------------------------------------------------------------------------------
>
> Key: ARROW-5169
> URL: https://issues.apache.org/jira/browse/ARROW-5169
> Project: Apache Arrow
> Issue Type: Bug
> Components: Python
> Affects Versions: 0.13.0
> Reporter: giacomo
> Assignee: Joris Van den Bossche
> Priority: Major
> Labels: pull-request-available
> Fix For: 0.14.0
>
> Time Spent: 20m
> Remaining Estimate: 0h
>
> In version 0.13.0, the {{Table.from_pandas}} function modifies the input
> schema by making all non-nullable types nullable.
> This can cause problems for example with this code:
> {code}
> df = pd.DataFrame(list(range(200)), columns=['numcol'])
> schema = pa.schema([
> pa.field('numcol', pa.int64(), nullable=False),
> ])
> writer = pq.ParquetWriter(io.BytesIO(), schema, version='2.0')
> table = pa.Table.from_pandas(df, schema=schema)
> writer.write_table(table)
> {code}
> Which fails due to the writer schema and the table schema being different.
> I believe the direct cause could be
> [https://github.com/apache/arrow/blob/master/python/pyarrow/table.pxi#L622]
> where nullable is set to True by default, resulting in the table schema being
> modified.
>
> Thanks for your valuable work on this library.
> Giacomo
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