Autodetector crashes on add/removal of tzinfo from DateTimeField default

[Camilo Ernesto Forero]

I wanted to add a default value to a DateTimeField, so I set default=datetime(2015, 7, 4, 8, 0 ) as an argument. When I ran makemigrations/migrate, I got a warning about naive timezones. I read about it and decided to set it as default=datetime(2015, 7, 4, 8, 0, tzinfo=timezone.get_default_timezone() ) (I imported django.utils.timezone) but when I tried to makemigrations and migrate I got an error can't compare offset-naive and offset-aware datetimes from old_field_dec != new_field_dec in django.autodetector.py.
To solve it I had to remove the default from the DateTimeField, migrate (got a warning again), add it again with the timezone enabled, and migrate again. That time it worked just fine.
It is worth noting that all of the fields currently in the database had their values already set, that I am using PostgreSQL and python 2.7.3

[Tim Graham]

Not sure the best to fix this.

[Markus Holtermann]

First, it's a rather uncommon use case to define an explicit datetime instead of now (i.e. a function). Second, I only see a possible fix by special casing datetime handling. That said, I think we should document this behavior as a known shortcoming until we find a suitable and practical solution.

[Mariusz Felisiak]

This ticket is not valid anymore. Python 3.5+ no longer raises TypeError when comparing naive and aware datetimes:

Python 3.5.10 (default, Jan 25 2021, 09:05:45) 
[GCC 9.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from datetime import datetime
>>> import pytz
>>> default=datetime(2015, 7, 4, 8, 0 )
>>> default2=datetime(2015, 7, 4, 8, 0, tzinfo=pytz.UTC)
>>> default != default2
True