Fixed flake8 errors.

django/db/migrations/migration.py

@@ -129,6 +129,7 @@ class Migration(object):
             operation.database_backwards(self.app_label, schema_editor, from_state, to_state)
         return project_state
 
+
 def swappable_dependency(value):
     """
     Turns a setting value into a dependency.

tests/migrations/test_autodetector.py

@@ -581,7 +581,7 @@ class AutodetectorTests(TestCase):
         the FK field before the model to maintain consistency.
         """
         before = self.make_project_state([self.author_with_publisher, self.publisher])
-        after = self.make_project_state([self.author_name]) # removes both the model and FK
+        after = self.make_project_state([self.author_name])  # removes both the model and FK
         autodetector = MigrationAutodetector(before, after)
         changes = autodetector._detect_changes()
         # Right number of migrations?
@@ -603,7 +603,7 @@ class AutodetectorTests(TestCase):
         the field before the model to maintain consistency.
         """
         before = self.make_project_state([self.book_with_multiple_authors_through_attribution, self.author_name, self.attribution])
-        after = self.make_project_state([self.book_with_no_author, self.author_name]) # removes both the through model and ManyToMany
+        after = self.make_project_state([self.book_with_no_author, self.author_name])  # removes both the through model and ManyToMany
         autodetector = MigrationAutodetector(before, after)
         changes = autodetector._detect_changes()
         # Right number of migrations?

tests/migrations/test_state.py

@@ -297,18 +297,21 @@ class StateTests(TestCase):
 
         class Author(models.Model):
             name = models.TextField()
+
             class Meta:
                 app_label = "migrations"
                 apps = new_apps
 
         class Book(models.Model):
             author = models.ForeignKey(Author)
+
             class Meta:
                 app_label = "migrations"
                 apps = new_apps
 
         class Magazine(models.Model):
             authors = models.ManyToManyField(Author)
+
             class Meta:
                 app_label = "migrations"
                 apps = new_apps