Using the "Factory" timezone on systems that use the system zoneinfo database can cause problems

[knobix]

On some systems, e.g. FreeBSD, if the system installied zoneinfo database is used this can lead to ValueError exceptions if using the Factory timezone.

The affected line is: https://github.com/mfogel/django-timezone-field/blob/main/timezone_field/backends/zoneinfo.py#L21

Here's a way to reproduce the issue:

import zoneinfo

print("Current TZPATH: {}".format(zoneinfo.TZPATH))
try:
    print("ZoneInfo: {}".format(zoneinfo.ZoneInfo('Factory')))
except Exception as error:
    print("An error occurred: {}".format(error))
    pass

Output:

Current TZPATH: ('/usr/share/zoneinfo', '/usr/lib/zoneinfo', '/usr/share/lib/zoneinfo', '/etc/zoneinfo')
An error occurred: Invalid STD format in b'<Local time zone must be set--use tzsetup>0'`

If using the tzdata package the problem doesn't occur:

import zoneinfo

zoneinfo.reset_tzpath(["/usr/local/lib/python3.9/site-packages/tzdata/zoneinfo/"])
print("Current TZPATH: {}".format(zoneinfo.TZPATH))
print("ZoneInfo: {}".format(zoneinfo.ZoneInfo('Factory')))

Output:

Current TZPATH: ('/usr/local/lib/python3.9/site-packages/tzdata/zoneinfo/',)
ZoneInfo: Factory

The described behavior was observed on FreeBSD 12.4-RELEASE, 13.2-RELEASE and 14.0-BETA4 with Python 3.9.18.

[mfogel]

Thanks for the bug report and fix @knobix ! Merged.