BUG: DataFrame with index having tzlocal() timezone could not be saved to parquet

[vfilimonov]

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If Dataframe has index which timezone is set to dateutil.tz.tzlocal(), it could not be saved to parquet.

It might be related to #24310

Code Sample, a copy-pastable example

from dateutil.tz import tzlocal
ind = pd.date_range('2020-02-01','2020-04-14').tz_localize(tzlocal())
x = pd.DataFrame([[1,2]]*len(ind), index=ind, columns=['A','B'])
x.to_parquet('tmp.parquet')

Problem description

The code raises ValueError: Unable to convert timezone "tzlocal()" to string.

However saving to e.g. CSV works well:

x.to_csv('tmp.csv')

Output of pd.show_versions()

Details

INSTALLED VERSIONS

commit : None
python : 3.7.1.final.0
python-bits : 64
OS : Darwin
OS-release : 18.7.0
machine : x86_64
processor : i386
byteorder : little
LC_ALL : en_US.UTF-8
LANG : en_US.UTF-8
LOCALE : en_US.UTF-8

pandas : 1.0.3
numpy : 1.18.2
pytz : 2019.3
dateutil : 2.8.1
pip : 20.0.2
setuptools : 42.0.1.post20191125
Cython : None
pytest : 5.3.0
hypothesis : None
sphinx : 2.2.0
blosc : None
feather : None
xlsxwriter : None
lxml.etree : 4.4.1
html5lib : None
pymysql : 0.9.3
psycopg2 : 2.8.5 (dt dec pq3 ext lo64)
jinja2 : 2.10.1
IPython : 7.13.0
pandas_datareader: None
bs4 : 4.6.3
bottleneck : None
fastparquet : 0.3.2
gcsfs : None
lxml.etree : 4.4.1
matplotlib : 3.1.3
numexpr : 2.7.0
odfpy : None
openpyxl : None
pandas_gbq : None
pyarrow : 0.16.0
pytables : None
pytest : 5.3.0
pyxlsb : None
s3fs : 0.4.2
scipy : 1.3.1
sqlalchemy : 1.3.13
tables : 3.4.4
tabulate : None
xarray : None
xlrd : 1.1.0
xlwt : None
xlsxwriter : None
numba : 0.46.0

[jorisvandenbossche]

@vfilimonov dateutil timezones are currently not supported by pyarrow, see https://issues.apache.org/jira/browse/ARROW-5248

So the best option, for now, is to convert the timezone to a datetime.timezone fixed offset of pytz timezone.

[vfilimonov]

Thank you for quick response @jorisvandenbossche!

What would be the easiest way to convert index to fixed offset?

I could think of a workaround by iterating over index and parsing strings:

from dateutil.tz import tzlocal
ind = pd.date_range('2020-02-01','2020-04-14').tz_localize(tzlocal())

ind = [pd.Timestamp(str(_)) for _ in ind]

[jbrockmendel]

@jorisvandenbossche is there any prospect of this being supported in pyarrow? if not it might make sense to add a helpful message for this case?