[Python] Tzinfo - string roundtrip fails on pytz.StaticTzInfo objects

[asfimport]

Timezone roundtrip fails with pytz.StaticTzInfo objects on master:

tz = pytz.timezone('Etc/GMT+1')
pa.lib.string_to_tzinfo(pa.lib.tzinfo_to_string(tz))

---------------------------------------------------------------------------
UnknownTimeZoneError                      Traceback (most recent call last)
<ipython-input-4-b890180b2fad> in <module>
----> 1 pa.lib.string_to_tzinfo(pa.lib.tzinfo_to_string(tz))

~/Workspace/arrow/python/pyarrow/types.pxi in pyarrow.lib.string_to_tzinfo()
   1838         Time zone object
   1839     """
-> 1840     cdef PyObject* tz = GetResultValue(StringToTzinfo(name.encode('utf-8')))
   1841     return PyObject_to_object(tz)
   1842

~/Workspace/arrow/python/pyarrow/error.pxi in pyarrow.lib.pyarrow_internal_check_status()
    120 cdef api int pyarrow_internal_check_status(const CStatus& status) \
    121         nogil except -1:
--> 122     return check_status(status)

~/.conda/envs/arrow38/lib/python3.8/site-packages/pytz/__init__.py in timezone(zone)
    179                 fp.close()
    180         else:
--> 181             raise UnknownTimeZoneError(zone)
    182
    183     return _tzinfo_cache[zone]

UnknownTimeZoneError: '-01'

Reporter: Krisztian Szucs / @kszucs
Assignee: Krisztian Szucs / @kszucs

Related issues:

• [C++][Python] Refactor python to arrow conversions based on a reusable conversion API (is fixed by)

_{Note: This issue was originally created as ARROW-9993. Please see the migration documentation for further details.}

[asfimport]

Joris Van den Bossche / @jorisvandenbossche:
Note that there are other timezones that won't roundtrip completely "faithfully" as well, because we don't keep track of the original python class/library that was used. Eg we tend to prefer pytz, so a datetime.timezone gets becomes a pytz timezone on roundtrip:

In [10]: import datetime

In [11]: tz = datetime.timezone(datetime.timedelta(hours=1))

In [12]: print(tz)
UTC+01:00

In [13]: pa.lib.tzinfo_to_string(tz)
Out[13]: '+01:00'

In [14]: roundtripped = pa.lib.string_to_tzinfo(pa.lib.tzinfo_to_string(tz))

In [15]: roundtripped
Out[15]: pytz.FixedOffset(60)

In [16]: tz == roundtripped
Out[16]: False

[asfimport]

Krisztian Szucs / @kszucs:
My goal was to prevent raising from a roundtrip rather than reproducing the exact value (which would be much harder).