Unnecessary migrations with Python3

[Torsten Bronger]

With Python3, "manage.py makemigrations" may under certain circumstances never be satisfied and always wants to create new migrations.

Steps to reproduce:

git clone https://github.com/juliabase/juliabase.git
cd juliabase
python3 manage.py makemigrations institute
python3 manage.py makemigrations institute
python3 manage.py makemigrations institute
...

Every time "makemigrations" is called, a new migration file is created. Apparently, Django+Python3 does not recognise that the Meta options of the latest migration and the current model classes are equivalent.

[Aymeric Augustin]

This may be because the definition of models changes every time you run the project e.g. using default=timezone.now() instead of default=timezone.now will trigger this behavior.

Can you provide one of the migrations? This will make it easier to see what changes and whether it's a bug in your code or in Django.

[Baptiste Mispelon]

Please provide a reduced set of models for your issue.

Your project is really big and has a ton of unspecified dependencies which makes it really hard to reproduce what you're describing.

I hacked around and managed to reproduce the "infinite migration" problem you're describing and I believe it might be caused by your generate_permissions function.
If I remove the custom permissions in ​https://github.com/juliabase/juliabase/blob/master/institute/models/depositions.py#L58, then the migration autodetector stops detecting that model.

[Baptiste Mispelon]

I think I got it.

In your generate_permissions function, you're iterating over a set. In recent versions of Python, the iteration order of sets (and dictionaries) is randomized and will change between separate runs.

Because of this, the order of you model's permissions is different every time so the autodetector picks up that change.

I don't believe that's a bug in Django's code. Changing from a set to a tuple in your code should fix the issue for you.

Thanks.

[Torsten Bronger]

Thank you, and sorry for the noise!