makemigrations: AttributeError: 'bytes' object has no attribute 'pattern' (Django 1.8/Python 3.4)

[Luis Diego García]

I added two DateTimeFields to my model and wanted to run makemigrations.

Got this error:

Traceback (most recent call last):
  File "./manage.py", line 11, in <module>
    execute_from_command_line(sys.argv)
  File "/home/areca/venv/lf2/lib/python3.4/site-packages/django/core/management/__init__.py", line 338, in execute_from_command_line
    utility.execute()
  File "/home/areca/venv/lf2/lib/python3.4/site-packages/django/core/management/__init__.py", line 330, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/home/areca/venv/lf2/lib/python3.4/site-packages/django/core/management/base.py", line 390, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/home/areca/venv/lf2/lib/python3.4/site-packages/django/core/management/base.py", line 441, in execute
    output = self.handle(*args, **options)
  File "/home/areca/venv/lf2/lib/python3.4/site-packages/django/core/management/commands/makemigrations.py", line 125, in handle
    migration_name=self.migration_name,
  File "/home/areca/venv/lf2/lib/python3.4/site-packages/django/db/migrations/autodetector.py", line 43, in changes
    changes = self._detect_changes(convert_apps, graph)
  File "/home/areca/venv/lf2/lib/python3.4/site-packages/django/db/migrations/autodetector.py", line 186, in _detect_changes
    self.generate_altered_fields()
  File "/home/areca/venv/lf2/lib/python3.4/site-packages/django/db/migrations/autodetector.py", line 850, in generate_altered_fields
    if old_field_dec != new_field_dec:
  File "/home/areca/venv/lf2/lib/python3.4/site-packages/django/core/validators.py", line 55, in __eq__
    self.regex.pattern == other.regex.pattern and
AttributeError: 'bytes' object has no attribute 'pattern'

Switched to a Python 2.7 environment and the error doesn't happen.

[Claude Paroz]

It will be difficult to guess what's happening without more information. What are the compared validators? It might be that your migration files contain some unfortunate byte strings (b'...').

[Dmitry Vlasov]

I get same problem, when porting my code to python 3.

Django on python2 create migration with byte-strings in code:

apps/post/migrations/0001_initial.py:                ('picture', models.ImageField(upload_to=b'images/posts/%Y_%m/%d', null=True, verbose_name='Picture', blank=True)),
apps/post/migrations/0001_initial.py:                ('lang_code', models.ForeignKey(default=b'en', verbose_name='Language', to='account.Language')),

And when we run it in python3 environ it crashes.

Works for me fix:

$ find apps -type f -exec sed -i "s/{b'/{'/g" {} \;        
$ find apps -type f -exec sed -i "s/(b'/('/g" {} \;
$ find apps -type f -exec sed -i "s/ b'/ '/g" {} \;
$ find apps -type f -exec sed -i "s/=b'/='/g" {} \;
$ find apps -type f -exec sed -i "s/\[b'/\['/g" {} \;

[Tim Graham]

The problem in the last comment is described in #24949.