[jira] [Created] (ARROW-9962) [Python] Conversion to pandas with index column using fixed timezone fails

["Joris Van den Bossche (Jira)" <ji...@apache.org>]

Joris Van den Bossche created ARROW-9962:
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             Summary: [Python] Conversion to pandas with index column using fixed timezone fails
                 Key: ARROW-9962
                 URL: https://issues.apache.org/jira/browse/ARROW-9962
             Project: Apache Arrow
          Issue Type: Bug
          Components: Python
            Reporter: Joris Van den Bossche


From https://github.com/pandas-dev/pandas/issues/35997: it seems we are handling a normal column and index column differently in the conversion to pandas.

{code}
In [5]: import pandas as pd
   ...: from datetime import datetime, timezone
   ...: 
   ...: df = pd.DataFrame([[datetime.now(timezone.utc), datetime.now(timezone.utc)]], columns=['date_index', 'date_column'])
   ...: table = pa.Table.from_pandas(df.set_index('date_index'))
   ...: 

In [6]: table
Out[6]: 
pyarrow.Table
date_column: timestamp[ns, tz=+00:00]
date_index: timestamp[ns, tz=+00:00]

In [7]: table.to_pandas()
...
UnknownTimeZoneError: '+00:00'
{code}

So this happens specifically for "fixed offset" timezones, and only for index columns (eg {{table.select(["date_column"]).to_pandas()}} works fine).

It seems this is because for columns we use our helper {{make_tz_aware}} to convert the string "+01:00" to a python timezone, which is then understood by pandas (the string is not handled by pandas). But for the index column we fail to do this.



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