diff --git a/django/core/management/commands/flush.py b/django/core/management/commands/flush.py
index 093c6db7b9..bcadb9671a 100644
--- a/django/core/management/commands/flush.py
+++ b/django/core/management/commands/flush.py
@@ -9,7 +9,6 @@ from django.core.management.sql import sql_flush, emit_post_sync_signal
 from django.utils.importlib import import_module
 
 
-
 class Command(NoArgsCommand):
     option_list = NoArgsCommand.option_list + (
         make_option('--noinput', action='store_false', dest='interactive', default=True,
diff --git a/django/core/management/sql.py b/django/core/management/sql.py
index 86d91fa8b7..01fc20fd4c 100644
--- a/django/core/management/sql.py
+++ b/django/core/management/sql.py
@@ -111,7 +111,9 @@ def sql_flush(style, connection, only_django=False):
         tables = connection.introspection.django_table_names(only_existing=True)
     else:
         tables = connection.introspection.table_names()
-    statements = connection.ops.sql_flush(style, tables, connection.introspection.sequence_list())
+    statements = connection.ops.sql_flush(
+        style, tables, connection.introspection.sequence_list()
+    )
     return statements
 
 def sql_custom(app, style, connection):
diff --git a/django/db/backends/__init__.py b/django/db/backends/__init__.py
index 2843e0d4c3..25587a7526 100644
--- a/django/db/backends/__init__.py
+++ b/django/db/backends/__init__.py
@@ -615,7 +615,12 @@ class BaseDatabaseIntrospection(object):
                 tables.add(model._meta.db_table)
                 tables.update([f.m2m_db_table() for f in model._meta.local_many_to_many])
         if only_existing:
-            tables = [t for t in tables if self.table_name_converter(t) in self.table_names()]
+            existing_tables = self.table_names()
+            tables = [
+                t
+                for t in tables
+                if self.table_name_converter(t) in existing_tables
+            ]
         return tables
 
     def installed_models(self, tables):
diff --git a/django/db/backends/sqlite3/introspection.py b/django/db/backends/sqlite3/introspection.py
index c243e58c8e..7f14941abf 100644
--- a/django/db/backends/sqlite3/introspection.py
+++ b/django/db/backends/sqlite3/introspection.py
@@ -4,7 +4,7 @@ from django.db.backends import BaseDatabaseIntrospection
 # This light wrapper "fakes" a dictionary interface, because some SQLite data
 # types include variables in them -- e.g. "varchar(30)" -- and can't be matched
 # as a simple dictionary lookup.
-class FlexibleFieldLookupDict:
+class FlexibleFieldLookupDict(object):
     # Maps SQL types to Django Field types. Some of the SQL types have multiple
     # entries here because SQLite allows for anything and doesn't normalize the
     # field type; it uses whatever was given.
@@ -138,4 +138,3 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
                  'null_ok': not field[3],
                  'pk': field[5]     # undocumented
                  } for field in cursor.fetchall()]
-