django/contrib/auth/migrations/0004_alter_user_username_opts.py

from django.contrib.auth import validators
from django.db import migrations, models


class Migration(migrations.Migration):

    dependencies = [
        ('auth', '0003_alter_user_email_max_length'),
    ]

    # No database changes; modifies validators and error_messages (#13147).
    operations = [
        migrations.AlterField(
            model_name='user',
            name='username',
            field=models.CharField(
                error_messages={'unique': 'A user with that username already exists.'}, max_length=30,
                validators=[validators.UnicodeUsernameValidator()],
                help_text='Required. 30 characters or fewer. Letters, digits and @/./+/-/_ only.',
                unique=True, verbose_name='username'
            ),
        ),
    ]