Django 1.11 and Python 3.6 causes error in migration

[tim-schilling]

We recently upgraded to django 1.11 and python 3.6. This caused a migration that should have ran without any problem. However, due to django's field internals keeping values as bytes rather than unicode this errors out in _get_python_and_db_repr as there is no handler for a bytes type.

Stacktrace from migration:

 File "./manage.py", line 10, in <module>
    execute_from_command_line(sys.argv)
  File "/project/lib/python3.6/site-packages/django/core/management/__init__.py", line 363, in execute_from_command_line
    utility.execute()
  File "/project/lib/python3.6/site-packages/django/core/management/__init__.py", line 355, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/project/lib/python3.6/site-packages/django/core/management/base.py", line 283, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/project/lib/python3.6/site-packages/django/core/management/base.py", line 330, in execute
    output = self.handle(*args, **options)
  File "/project/lib/python3.6/site-packages/django/core/management/commands/migrate.py", line 204, in handle
    fake_initial=fake_initial,
  File "/project/lib/python3.6/site-packages/django/db/migrations/executor.py", line 115, in migrate
    state = self._migrate_all_forwards(state, plan, full_plan, fake=fake, fake_initial=fake_initial)
  File "/project/lib/python3.6/site-packages/django/db/migrations/executor.py", line 145, in _migrate_all_forwards
    state = self.apply_migration(state, migration, fake=fake, fake_initial=fake_initial)
  File "/project/lib/python3.6/site-packages/django/db/migrations/executor.py", line 244, in apply_migration
    state = migration.apply(state, schema_editor)
  File "/project/lib/python3.6/site-packages/django/db/migrations/migration.py", line 129, in apply
    operation.database_forwards(self.app_label, schema_editor, old_state, project_state)
  File "/project/lib/python3.6/site-packages/django/db/migrations/operations/fields.py", line 215, in database_forwards
    schema_editor.alter_field(from_model, from_field, to_field)
  File "/project/lib/python3.6/site-packages/django/db/backends/base/schema.py", line 513, in alter_field
    old_db_params, new_db_params, strict)
  File "/project/lib/python3.6/site-packages/django/db/backends/postgresql/schema.py", line 112, in _alter_field
    new_db_params, strict,
  File "/project/lib/python3.6/site-packages/django/db/backends/base/schema.py", line 602, in _alter_field
    old_default = self.effective_default(old_field)
  File "/project/lib/python3.6/site-packages/django/db/backends/base/schema.py", line 206, in effective_default
    default = field.get_default()
  File "/project/lib/python3.6/site-packages/timezone_field/fields.py", line 92, in get_default
    return self._get_python_and_db_repr(value)[0]
  File "/project/lib/python3.6/site-packages/timezone_field/fields.py", line 118, in _get_python_and_db_repr
    raise ValidationError("Invalid timezone '%s'" % value)
django.core.exceptions.ValidationError: ["Invalid timezone 'b'UTC''"]

PR to follow.

[mikekeda]

I have Django 1.11.2 and Python 3.4.3
python manage.py makemigrations dosen't see the field

"No changes detected"

[tim-schilling]

Did you upgrade to that environment then run makemigrations?

[TurboBelka]

Does it work now with Django 1.11?

[ftvkun]

I fixed that by changing fields.TimeZoneField(default=b'XXX') to fields.TimeZoneField(default='XXX') in our old migrations