Squashing migrations with Python 2.7 adds bytestring prefix to ManyToManyField 'to' values which fails to run on Python 3

[Brian May]

In attempting a work around for #26384 by squashing the commits, I found another problem:

E           AssertionError: ManyToManyField(b'spud.album') is invalid. First parameter to ManyToManyField must be either a model, a model name, or the string 'self'

I believe the problem is that it used a byte value instead of a string.

        migrations.AddField(
            model_name='photo',
            name='albums',
            field=models.ManyToManyField(related_name='photos', through='spud.photo_album', to=b'spud.album'),
        ),

This works fine with Python 2.7 but not with Python 3.4.

The original before squashing was ok:

        migrations.AddField(
            model_name='photo',
            name='albums',
            field=models.ManyToManyField(related_name='photos', through='spud.photo_album', to='spud.album'),
            preserve_default=True,
        ),

[Brian May]

Forgot to mention, the squashed commits where created with Python 2.7

[Brian May]

Looks like squashing the migration in Python3.4 creates a migration that will work with all versions of Python.

Curiously though with Python 2.7 it sets initial=True on the migration, but when squashed with Python3.4 it doesn't.

[Tim Graham]

I can reproduce the issue but cannot track where the bytestring is coming from. A more minimal sample project may help but I think the issue isn't high priority since Python 2 support will be dropped soon.

[Tim Graham]

Closing given Python 2 support will be dropped in master in a couple weeks.