Fix breakage caused by change in django-timezone-field

[davidrothera]

In mfogel/django-timezone-field@0c6a6ba the CHOICES property was removed, it was replaced with two new fields default_tzs and default_choices. The latter of the two is the same choices as before and so we just use that now instead.

Fixes #377

[arnau126]

With this change, django-celery-beat will no longer work with django-timezone-field==4.0.

I see two options:

1. Modify the minimum required version of django-timezone-field in requirements: django-timezone-field>=4.1,<5.0
2. Make the code work with both versions: modify django_celery_beat/models.py so it uses CHOICES or default_choices depending on the django-timezone-field version.

[davidrothera]

Great point @arnau126, I had meant to pin the requirements but forgot in the initial PR

[davidrothera]

Another option would be to parse and gate by using the timezone_field.__version__ field with something like the packaging.version.parse method but it would require another third-party dependency (one already used by setup tools though so its more than likely already installed)

[auvipy]

I guess this also need change in model migrations?

[davidrothera]

@auvipy I don't think any other changes will be needed, the tuples outputted by TimeZoneField.CHOICES and default_choices are the same and so the data should be the same.

[davidrothera]

(venv) ~/D/django-celery-beat ❯❯❯ python3.9 manage.py makemigrations                                                                         master
No changes detected

[tasiotas]

hi, Im not quite knowlegable with github, PR and merging.
I am using:
django-celery-beat 2.1.0
django-timezone-field 4.1.1

and getting this error:

django_celery_beat\models.py", line 60, in crontab_schedule_celery_timezone
    choice[0].zone for choice in timezone_field.TimeZoneField.CHOICES
AttributeError: type object 'TimeZoneField' has no attribute 'CHOICES'

Is there anything im missing?

[arnau126]

This PR has fixed your error.
It is merged, but not released.
Until then (django-celery-beat 2.1.1 is released) downgrade django-timezone-field to 4.0.

[tasiotas]

This PR has fixed your error.
It is merged, but not released.
Until then (django-celery-beat 2.1.1 is released) downgrade django-timezone-field to 4.0.

Thank you!