diff --git a/django/contrib/auth/models.py b/django/contrib/auth/models.py
index 84088f6525..aa0669ffe0 100644
--- a/django/contrib/auth/models.py
+++ b/django/contrib/auth/models.py
@@ -110,8 +110,11 @@ class Group(models.Model):
     messages.
     """
     name = models.CharField(_('name'), max_length=80, unique=True)
-    permissions = models.ManyToManyField(Permission,
-        verbose_name=_('permissions'), blank=True)
+    permissions = models.ManyToManyField(
+        Permission,
+        verbose_name=_('permissions'),
+        blank=True,
+    )
 
     objects = GroupManager()
 
@@ -197,18 +200,33 @@ class PermissionsMixin(models.Model):
     A mixin class that adds the fields and methods necessary to support
     Django's Group and Permission model using the ModelBackend.
     """
-    is_superuser = models.BooleanField(_('superuser status'), default=False,
-        help_text=_('Designates that this user has all permissions without '
-                    'explicitly assigning them.'))
-    groups = models.ManyToManyField(Group, verbose_name=_('groups'),
-        blank=True, help_text=_('The groups this user belongs to. A user will '
-                                'get all permissions granted to each of '
-                                'their groups.'),
-        related_name="user_set", related_query_name="user")
-    user_permissions = models.ManyToManyField(Permission,
-        verbose_name=_('user permissions'), blank=True,
+    is_superuser = models.BooleanField(
+        _('superuser status'),
+        default=False,
+        help_text=_(
+            'Designates that this user has all permissions without '
+            'explicitly assigning them.'
+        ),
+    )
+    groups = models.ManyToManyField(
+        Group,
+        verbose_name=_('groups'),
+        blank=True,
+        help_text=_(
+            'The groups this user belongs to. A user will get all permissions '
+            'granted to each of their groups.'
+        ),
+        related_name="user_set",
+        related_query_name="user",
+    )
+    user_permissions = models.ManyToManyField(
+        Permission,
+        verbose_name=_('user permissions'),
+        blank=True,
         help_text=_('Specific permissions for this user.'),
-        related_name="user_set", related_query_name="user")
+        related_name="user_set",
+        related_query_name="user",
+    )
 
     class Meta:
         abstract = True
@@ -274,27 +292,38 @@ class AbstractUser(AbstractBaseUser, PermissionsMixin):
 
     Username, password and email are required. Other fields are optional.
     """
-    username = models.CharField(_('username'), max_length=30, unique=True,
-        help_text=_('Required. 30 characters or fewer. Letters, digits and '
-                    '@/./+/-/_ only.'),
+    username = models.CharField(
+        _('username'),
+        max_length=30,
+        unique=True,
+        help_text=_('Required. 30 characters or fewer. Letters, digits and @/./+/-/_ only.'),
         validators=[
-            validators.RegexValidator(r'^[\w.@+-]+$',
-                                      _('Enter a valid username. '
-                                        'This value may contain only letters, numbers '
-                                        'and @/./+/-/_ characters.'), 'invalid'),
+            validators.RegexValidator(
+                r'^[\w.@+-]+$',
+                _('Enter a valid username. This value may contain only '
+                  'letters, numbers ' 'and @/./+/-/_ characters.')
+            ),
         ],
         error_messages={
             'unique': _("A user with that username already exists."),
-        })
+        },
+    )
     first_name = models.CharField(_('first name'), max_length=30, blank=True)
     last_name = models.CharField(_('last name'), max_length=30, blank=True)
     email = models.EmailField(_('email address'), blank=True)
-    is_staff = models.BooleanField(_('staff status'), default=False,
-        help_text=_('Designates whether the user can log into this admin '
-                    'site.'))
-    is_active = models.BooleanField(_('active'), default=True,
-        help_text=_('Designates whether this user should be treated as '
-                    'active. Unselect this instead of deleting accounts.'))
+    is_staff = models.BooleanField(
+        _('staff status'),
+        default=False,
+        help_text=_('Designates whether the user can log into this admin site.'),
+    )
+    is_active = models.BooleanField(
+        _('active'),
+        default=True,
+        help_text=_(
+            'Designates whether this user should be treated as active. '
+            'Unselect this instead of deleting accounts.'
+        ),
+    )
     date_joined = models.DateTimeField(_('date joined'), default=timezone.now)
 
     objects = UserManager()