diff --git a/django/db/__init__.py b/django/db/__init__.py
index 72adf60d66bda..e1af430dc24e3 100644
--- a/django/db/__init__.py
+++ b/django/db/__init__.py
@@ -1,20 +1,25 @@
 import warnings
 
 from django.core import signals
-from django.db.utils import (DEFAULT_DB_ALIAS,
-    DataError, OperationalError, IntegrityError, InternalError,
-    ProgrammingError, NotSupportedError, DatabaseError,
-    InterfaceError, Error,
-    load_backend, ConnectionHandler, ConnectionRouter)
+from django.db.utils import (DEFAULT_DB_ALIAS, DataError, OperationalError,
+    IntegrityError, InternalError, ProgrammingError, NotSupportedError,
+    DatabaseError, InterfaceError, Error, load_backend,
+    ConnectionHandler, ConnectionRouter)
 from django.utils.functional import cached_property
 
-__all__ = ('backend', 'connection', 'connections', 'router', 'DatabaseError',
-    'IntegrityError', 'DEFAULT_DB_ALIAS')
+
+__all__ = [
+    'backend', 'connection', 'connections', 'router', 'DatabaseError',
+    'IntegrityError', 'InternalError', 'ProgrammingError', 'DataError',
+    'NotSupportedError', 'Error', 'InterfaceError', 'OperationalError',
+    'DEFAULT_DB_ALIAS'
+]
 
 connections = ConnectionHandler()
 
 router = ConnectionRouter()
 
+
 # `connection`, `DatabaseError` and `IntegrityError` are convenient aliases
 # for backend bits.
 
@@ -70,6 +75,7 @@ def __delattr__(self, name):
 
 backend = DefaultBackendProxy()
 
+
 def close_connection(**kwargs):
     warnings.warn(
         "close_connection is superseded by close_old_connections.",
@@ -83,12 +89,14 @@ def close_connection(**kwargs):
         transaction.abort(conn)
         connections[conn].close()
 
+
 # Register an event to reset saved queries when a Django request is started.
 def reset_queries(**kwargs):
     for conn in connections.all():
         conn.queries = []
 signals.request_started.connect(reset_queries)
 
+
 # Register an event to reset transaction state and close connections past
 # their lifetime. NB: abort() doesn't do anything outside of a transaction.
 def close_old_connections(**kwargs):
diff --git a/django/db/backends/__init__.py b/django/db/backends/__init__.py
index 28a4a48a9f8fc..a553351c5c7ba 100644
--- a/django/db/backends/__init__.py
+++ b/django/db/backends/__init__.py
@@ -1167,6 +1167,7 @@ def modify_insert_params(self, placeholders, params):
     'name type_code display_size internal_size precision scale null_ok'
 )
 
+
 class BaseDatabaseIntrospection(object):
     """
     This class encapsulates all backend-specific introspection utilities
diff --git a/django/db/backends/creation.py b/django/db/backends/creation.py
index 6f66cfb7ca905..50e45c0e75050 100644
--- a/django/db/backends/creation.py
+++ b/django/db/backends/creation.py
@@ -251,12 +251,13 @@ def sql_remove_table_constraints(self, model, references_to_delete, style):
             r_col = model._meta.get_field(f.rel.field_name).column
             r_name = '%s_refs_%s_%s' % (
                 col, r_col, self._digest(table, r_table))
-            output.append('%s %s %s %s;' % \
-                (style.SQL_KEYWORD('ALTER TABLE'),
+            output.append('%s %s %s %s;' % (
+                style.SQL_KEYWORD('ALTER TABLE'),
                 style.SQL_TABLE(qn(table)),
                 style.SQL_KEYWORD(self.connection.ops.drop_foreignkey_sql()),
                 style.SQL_FIELD(qn(truncate_name(
-                    r_name, self.connection.ops.max_name_length())))))
+                    r_name, self.connection.ops.max_name_length())))
+            ))
         del references_to_delete[model]
         return output
 
diff --git a/django/db/backends/dummy/base.py b/django/db/backends/dummy/base.py
index 9a220ffd8b5ca..3e6d3e4c5a2ba 100644
--- a/django/db/backends/dummy/base.py
+++ b/django/db/backends/dummy/base.py
@@ -8,33 +8,43 @@
 """
 
 from django.core.exceptions import ImproperlyConfigured
-from django.db.backends import *
+from django.db.backends import (BaseDatabaseOperations, BaseDatabaseClient,
+    BaseDatabaseIntrospection, BaseDatabaseWrapper, BaseDatabaseFeatures,
+    BaseDatabaseValidation)
 from django.db.backends.creation import BaseDatabaseCreation
 
+
 def complain(*args, **kwargs):
     raise ImproperlyConfigured("settings.DATABASES is improperly configured. "
                                "Please supply the ENGINE value. Check "
                                "settings documentation for more details.")
 
+
 def ignore(*args, **kwargs):
     pass
 
+
 class DatabaseError(Exception):
     pass
 
+
 class IntegrityError(DatabaseError):
     pass
 
+
 class DatabaseOperations(BaseDatabaseOperations):
     quote_name = complain
 
+
 class DatabaseClient(BaseDatabaseClient):
     runshell = complain
 
+
 class DatabaseCreation(BaseDatabaseCreation):
     create_test_db = ignore
     destroy_test_db = ignore
 
+
 class DatabaseIntrospection(BaseDatabaseIntrospection):
     get_table_list = complain
     get_table_description = complain
@@ -42,6 +52,7 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
     get_indexes = complain
     get_key_columns = complain
 
+
 class DatabaseWrapper(BaseDatabaseWrapper):
     operators = {}
     # Override the base class implementations with null
diff --git a/django/db/backends/mysql/base.py b/django/db/backends/mysql/base.py
index d10be94f43969..2db746f40fb2e 100644
--- a/django/db/backends/mysql/base.py
+++ b/django/db/backends/mysql/base.py
@@ -36,8 +36,9 @@
     pytz = None
 
 from django.conf import settings
-from django.db import utils
-from django.db.backends import *
+from django.db import (utils, BaseDatabaseFeatures, BaseDatabaseOperations,
+    BaseDatabaseWrapper)
+from django.db.backends import util
 from django.db.backends.mysql.client import DatabaseClient
 from django.db.backends.mysql.creation import DatabaseCreation
 from django.db.backends.mysql.introspection import DatabaseIntrospection
@@ -57,6 +58,7 @@
 # It's impossible to import datetime_or_None directly from MySQLdb.times
 parse_datetime = conversions[FIELD_TYPE.DATETIME]
 
+
 def parse_datetime_with_timezone_support(value):
     dt = parse_datetime(value)
     # Confirm that dt is naive before overwriting its tzinfo.
@@ -64,6 +66,7 @@ def parse_datetime_with_timezone_support(value):
         dt = dt.replace(tzinfo=timezone.utc)
     return dt
 
+
 def adapt_datetime_with_timezone_support(value, conv):
     # Equivalent to DateTimeField.get_db_prep_value. Used only by raw SQL.
     if settings.USE_TZ:
@@ -98,6 +101,7 @@ def adapt_datetime_with_timezone_support(value, conv):
 # http://dev.mysql.com/doc/refman/5.0/en/news.html .
 server_version_re = re.compile(r'(\d{1,2})\.(\d{1,2})\.(\d{1,2})')
 
+
 # MySQLdb-1.2.1 and newer automatically makes use of SHOW WARNINGS on
 # MySQL-4.1 and newer, so the MysqlDebugWrapper is unnecessary. Since the
 # point is to raise Warnings as exceptions, this can be done with the Python
@@ -148,6 +152,7 @@ def __getattr__(self, attr):
     def __iter__(self):
         return iter(self.cursor)
 
+
 class DatabaseFeatures(BaseDatabaseFeatures):
     empty_fetchmany_value = ()
     update_can_self_select = False
@@ -204,6 +209,7 @@ def has_zoneinfo_database(self):
         cursor.execute("SELECT 1 FROM mysql.time_zone LIMIT 1")
         return cursor.fetchone() is not None
 
+
 class DatabaseOperations(BaseDatabaseOperations):
     compiler_module = "django.db.backends.mysql.compiler"
 
@@ -319,7 +325,7 @@ def sequence_reset_by_name_sql(self, style, sequences):
         # Truncate already resets the AUTO_INCREMENT field from
         # MySQL version 5.0.13 onwards. Refs #16961.
         if self.connection.mysql_version < (5, 0, 13):
-            return ["%s %s %s %s %s;" % \
+            return ["%s %s %s %s %s;" %
                     (style.SQL_KEYWORD('ALTER'),
                     style.SQL_KEYWORD('TABLE'),
                     style.SQL_TABLE(self.quote_name(sequence['table'])),
@@ -373,6 +379,7 @@ def bulk_insert_sql(self, fields, num_values):
         items_sql = "(%s)" % ", ".join(["%s"] * len(fields))
         return "VALUES " + ", ".join([items_sql] * num_values)
 
+
 class DatabaseWrapper(BaseDatabaseWrapper):
     vendor = 'mysql'
     operators = {
diff --git a/django/db/backends/mysql/client.py b/django/db/backends/mysql/client.py
index 1cf8ceef9c80d..8364c7b6e6d81 100644
--- a/django/db/backends/mysql/client.py
+++ b/django/db/backends/mysql/client.py
@@ -3,6 +3,7 @@
 
 from django.db.backends import BaseDatabaseClient
 
+
 class DatabaseClient(BaseDatabaseClient):
     executable_name = 'mysql'
 
@@ -37,4 +38,3 @@ def runshell(self):
             sys.exit(os.system(" ".join(args)))
         else:
             os.execvp(self.executable_name, args)
-
diff --git a/django/db/backends/mysql/compiler.py b/django/db/backends/mysql/compiler.py
index 4e033e3d931e0..b7d1d7b98d56b 100644
--- a/django/db/backends/mysql/compiler.py
+++ b/django/db/backends/mysql/compiler.py
@@ -22,20 +22,26 @@ def as_subquery_condition(self, alias, columns, qn):
         sql, params = self.as_sql()
         return '(%s) IN (%s)' % (', '.join(['%s.%s' % (qn(alias), qn2(column)) for column in columns]), sql), params
 
+
 class SQLInsertCompiler(compiler.SQLInsertCompiler, SQLCompiler):
     pass
 
+
 class SQLDeleteCompiler(compiler.SQLDeleteCompiler, SQLCompiler):
     pass
 
+
 class SQLUpdateCompiler(compiler.SQLUpdateCompiler, SQLCompiler):
     pass
 
+
 class SQLAggregateCompiler(compiler.SQLAggregateCompiler, SQLCompiler):
     pass
 
+
 class SQLDateCompiler(compiler.SQLDateCompiler, SQLCompiler):
     pass
 
+
 class SQLDateTimeCompiler(compiler.SQLDateTimeCompiler, SQLCompiler):
     pass
diff --git a/django/db/backends/mysql/creation.py b/django/db/backends/mysql/creation.py
index 3a57c29479ad2..b59b225f4f8cf 100644
--- a/django/db/backends/mysql/creation.py
+++ b/django/db/backends/mysql/creation.py
@@ -1,34 +1,35 @@
 from django.db.backends.creation import BaseDatabaseCreation
 
+
 class DatabaseCreation(BaseDatabaseCreation):
     # This dictionary maps Field objects to their associated MySQL column
     # types, as strings. Column-type strings can contain format strings; they'll
     # be interpolated against the values of Field.__dict__ before being output.
     # If a column type is set to None, it won't be included in the output.
     data_types = {
-        'AutoField':         'integer AUTO_INCREMENT',
-        'BinaryField':       'longblob',
-        'BooleanField':      'bool',
-        'CharField':         'varchar(%(max_length)s)',
+        'AutoField': 'integer AUTO_INCREMENT',
+        'BinaryField': 'longblob',
+        'BooleanField': 'bool',
+        'CharField': 'varchar(%(max_length)s)',
         'CommaSeparatedIntegerField': 'varchar(%(max_length)s)',
-        'DateField':         'date',
-        'DateTimeField':     'datetime',
-        'DecimalField':      'numeric(%(max_digits)s, %(decimal_places)s)',
-        'FileField':         'varchar(%(max_length)s)',
-        'FilePathField':     'varchar(%(max_length)s)',
-        'FloatField':        'double precision',
-        'IntegerField':      'integer',
-        'BigIntegerField':   'bigint',
-        'IPAddressField':    'char(15)',
+        'DateField': 'date',
+        'DateTimeField': 'datetime',
+        'DecimalField': 'numeric(%(max_digits)s, %(decimal_places)s)',
+        'FileField': 'varchar(%(max_length)s)',
+        'FilePathField': 'varchar(%(max_length)s)',
+        'FloatField': 'double precision',
+        'IntegerField': 'integer',
+        'BigIntegerField': 'bigint',
+        'IPAddressField': 'char(15)',
         'GenericIPAddressField': 'char(39)',
-        'NullBooleanField':  'bool',
-        'OneToOneField':     'integer',
+        'NullBooleanField': 'bool',
+        'OneToOneField': 'integer',
         'PositiveIntegerField': 'integer UNSIGNED',
         'PositiveSmallIntegerField': 'smallint UNSIGNED',
-        'SlugField':         'varchar(%(max_length)s)',
+        'SlugField': 'varchar(%(max_length)s)',
         'SmallIntegerField': 'smallint',
-        'TextField':         'longtext',
-        'TimeField':         'time',
+        'TextField': 'longtext',
+        'TimeField': 'time',
     }
 
     def sql_table_creation_suffix(self):
diff --git a/django/db/backends/mysql/introspection.py b/django/db/backends/mysql/introspection.py
index 548877e8e63a6..ec9f3e99f80f1 100644
--- a/django/db/backends/mysql/introspection.py
+++ b/django/db/backends/mysql/introspection.py
@@ -7,6 +7,7 @@
 
 foreign_key_re = re.compile(r"\sCONSTRAINT `[^`]*` FOREIGN KEY \(`([^`]*)`\) REFERENCES `([^`]*)` \(`([^`]*)`\)")
 
+
 class DatabaseIntrospection(BaseDatabaseIntrospection):
     data_types_reverse = {
         FIELD_TYPE.BLOB: 'TextField',
@@ -116,4 +117,3 @@ def get_indexes(self, cursor, table_name):
                 continue
             indexes[row[4]] = {'primary_key': (row[2] == 'PRIMARY'), 'unique': not bool(row[1])}
         return indexes
-
diff --git a/django/db/backends/mysql/validation.py b/django/db/backends/mysql/validation.py
index 2ce957cce7655..17b7cde75661d 100644
--- a/django/db/backends/mysql/validation.py
+++ b/django/db/backends/mysql/validation.py
@@ -1,5 +1,6 @@
 from django.db.backends import BaseDatabaseValidation
 
+
 class DatabaseValidation(BaseDatabaseValidation):
     def validate_field(self, errors, opts, f):
         """
diff --git a/django/db/backends/oracle/base.py b/django/db/backends/oracle/base.py
index 5e2b763f52ec1..04e70cfdb812e 100644
--- a/django/db/backends/oracle/base.py
+++ b/django/db/backends/oracle/base.py
@@ -7,11 +7,12 @@
 
 import decimal
 import re
+import platform
 import sys
 import warnings
 
+
 def _setup_environment(environ):
-    import platform
     # Cygwin requires some special voodoo to set the environment variables
     # properly so that Oracle will see them.
     if platform.system().upper().startswith('CYGWIN'):
@@ -90,6 +91,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     supports_tablespaces = True
     supports_sequence_reset = False
 
+
 class DatabaseOperations(BaseDatabaseOperations):
     compiler_module = "django.db.backends.oracle.compiler"
 
@@ -308,7 +310,7 @@ def quote_name(self, name):
         # Oracle puts the query text into a (query % args) construct, so % signs
         # in names need to be escaped. The '%%' will be collapsed back to '%' at
         # that stage so we aren't really making the name longer here.
-        name = name.replace('%','%%')
+        name = name.replace('%', '%%')
         return name.upper()
 
     def random_function_sql(self):
@@ -758,7 +760,7 @@ def __init__(self, connection):
 
     def _format_params(self, params):
         try:
-            return dict((k,OracleParam(v, self, True)) for k,v in params.items())
+            return dict((k, OracleParam(v, self, True)) for k, v in params.items())
         except AttributeError:
             return tuple([OracleParam(p, self, True) for p in params])
 
@@ -778,12 +780,12 @@ def _guess_input_sizes(self, params_list):
                 for i, value in enumerate(params):
                     if value.input_size:
                         sizes[i] = value.input_size
-            self.setinputsizes(*sizes)        
+            self.setinputsizes(*sizes)
 
     def _param_generator(self, params):
         # Try dict handling; if that fails, treat as sequence
         if hasattr(params, 'items'):
-            return dict((k, v.force_bytes) for k,v in params.items())
+            return dict((k, v.force_bytes) for k, v in params.items())
         else:
             return [p.force_bytes for p in params]
 
@@ -799,14 +801,14 @@ def _fix_for_params(self, query, params):
             query = convert_unicode(query, self.charset)
         elif hasattr(params, 'keys'):
             # Handle params as dict
-            args = dict((k, ":%s"%k) for k in params.keys())
+            args = dict((k, ":%s" % k) for k in params.keys())
             query = convert_unicode(query % args, self.charset)
         else:
             # Handle params as sequence
             args = [(':arg%d' % i) for i in range(len(params))]
             query = convert_unicode(query % tuple(args), self.charset)
         return query, self._format_params(params)
-        
+
     def execute(self, query, params=None):
         query, params = self._fix_for_params(query, params)
         self._guess_input_sizes([params])
@@ -825,9 +827,9 @@ def executemany(self, query, params=None):
         # uniform treatment for sequences and iterables
         params_iter = iter(params)
         query, firstparams = self._fix_for_params(query, next(params_iter))
-        # we build a list of formatted params; as we're going to traverse it 
+        # we build a list of formatted params; as we're going to traverse it
         # more than once, we can't make it lazy by using a generator
-        formatted = [firstparams]+[self._format_params(p) for p in params_iter]
+        formatted = [firstparams] + [self._format_params(p) for p in params_iter]
         self._guess_input_sizes(formatted)
         try:
             return self.cursor.executemany(query,
diff --git a/django/db/backends/oracle/client.py b/django/db/backends/oracle/client.py
index ccc64ebffc701..ac6b79041f761 100644
--- a/django/db/backends/oracle/client.py
+++ b/django/db/backends/oracle/client.py
@@ -3,6 +3,7 @@
 
 from django.db.backends import BaseDatabaseClient
 
+
 class DatabaseClient(BaseDatabaseClient):
     executable_name = 'sqlplus'
 
@@ -13,4 +14,3 @@ def runshell(self):
             sys.exit(os.system(" ".join(args)))
         else:
             os.execvp(self.executable_name, args)
-
diff --git a/django/db/backends/oracle/compiler.py b/django/db/backends/oracle/compiler.py
index cbee27951c9b0..d2d4cd3ac9db8 100644
--- a/django/db/backends/oracle/compiler.py
+++ b/django/db/backends/oracle/compiler.py
@@ -60,17 +60,22 @@ def as_sql(self, with_limits=True, with_col_aliases=False):
 class SQLInsertCompiler(compiler.SQLInsertCompiler, SQLCompiler):
     pass
 
+
 class SQLDeleteCompiler(compiler.SQLDeleteCompiler, SQLCompiler):
     pass
 
+
 class SQLUpdateCompiler(compiler.SQLUpdateCompiler, SQLCompiler):
     pass
 
+
 class SQLAggregateCompiler(compiler.SQLAggregateCompiler, SQLCompiler):
     pass
 
+
 class SQLDateCompiler(compiler.SQLDateCompiler, SQLCompiler):
     pass
 
+
 class SQLDateTimeCompiler(compiler.SQLDateTimeCompiler, SQLCompiler):
     pass
diff --git a/django/db/backends/oracle/creation.py b/django/db/backends/oracle/creation.py
index c7808e4849697..55f6ee4d7e4a2 100644
--- a/django/db/backends/oracle/creation.py
+++ b/django/db/backends/oracle/creation.py
@@ -5,9 +5,11 @@
 from django.db.backends.creation import BaseDatabaseCreation
 from django.utils.six.moves import input
 
+
 TEST_DATABASE_PREFIX = 'test_'
 PASSWORD = 'Im_a_lumberjack'
 
+
 class DatabaseCreation(BaseDatabaseCreation):
     # This dictionary maps Field objects to their associated Oracle column
     # types, as strings. Column-type strings can contain format strings; they'll
@@ -18,30 +20,30 @@ class DatabaseCreation(BaseDatabaseCreation):
     # output (the "qn_" prefix is stripped before the lookup is performed.
 
     data_types = {
-        'AutoField':                    'NUMBER(11)',
-        'BinaryField':                  'BLOB',
-        'BooleanField':                 'NUMBER(1) CHECK (%(qn_column)s IN (0,1))',
-        'CharField':                    'NVARCHAR2(%(max_length)s)',
-        'CommaSeparatedIntegerField':   'VARCHAR2(%(max_length)s)',
-        'DateField':                    'DATE',
-        'DateTimeField':                'TIMESTAMP',
-        'DecimalField':                 'NUMBER(%(max_digits)s, %(decimal_places)s)',
-        'FileField':                    'NVARCHAR2(%(max_length)s)',
-        'FilePathField':                'NVARCHAR2(%(max_length)s)',
-        'FloatField':                   'DOUBLE PRECISION',
-        'IntegerField':                 'NUMBER(11)',
-        'BigIntegerField':              'NUMBER(19)',
-        'IPAddressField':               'VARCHAR2(15)',
-        'GenericIPAddressField':        'VARCHAR2(39)',
-        'NullBooleanField':             'NUMBER(1) CHECK ((%(qn_column)s IN (0,1)) OR (%(qn_column)s IS NULL))',
-        'OneToOneField':                'NUMBER(11)',
-        'PositiveIntegerField':         'NUMBER(11) CHECK (%(qn_column)s >= 0)',
-        'PositiveSmallIntegerField':    'NUMBER(11) CHECK (%(qn_column)s >= 0)',
-        'SlugField':                    'NVARCHAR2(%(max_length)s)',
-        'SmallIntegerField':            'NUMBER(11)',
-        'TextField':                    'NCLOB',
-        'TimeField':                    'TIMESTAMP',
-        'URLField':                     'VARCHAR2(%(max_length)s)',
+        'AutoField': 'NUMBER(11)',
+        'BinaryField': 'BLOB',
+        'BooleanField': 'NUMBER(1) CHECK (%(qn_column)s IN (0,1))',
+        'CharField': 'NVARCHAR2(%(max_length)s)',
+        'CommaSeparatedIntegerField': 'VARCHAR2(%(max_length)s)',
+        'DateField': 'DATE',
+        'DateTimeField': 'TIMESTAMP',
+        'DecimalField': 'NUMBER(%(max_digits)s, %(decimal_places)s)',
+        'FileField': 'NVARCHAR2(%(max_length)s)',
+        'FilePathField': 'NVARCHAR2(%(max_length)s)',
+        'FloatField': 'DOUBLE PRECISION',
+        'IntegerField': 'NUMBER(11)',
+        'BigIntegerField': 'NUMBER(19)',
+        'IPAddressField': 'VARCHAR2(15)',
+        'GenericIPAddressField': 'VARCHAR2(39)',
+        'NullBooleanField': 'NUMBER(1) CHECK ((%(qn_column)s IN (0,1)) OR (%(qn_column)s IS NULL))',
+        'OneToOneField': 'NUMBER(11)',
+        'PositiveIntegerField': 'NUMBER(11) CHECK (%(qn_column)s >= 0)',
+        'PositiveSmallIntegerField': 'NUMBER(11) CHECK (%(qn_column)s >= 0)',
+        'SlugField': 'NVARCHAR2(%(max_length)s)',
+        'SmallIntegerField': 'NUMBER(11)',
+        'TextField': 'NCLOB',
+        'TimeField': 'TIMESTAMP',
+        'URLField': 'VARCHAR2(%(max_length)s)',
     }
 
     def __init__(self, connection):
@@ -183,7 +185,7 @@ def _execute_test_db_destruction(self, cursor, parameters, verbosity):
         statements = [
             'DROP TABLESPACE %(tblspace)s INCLUDING CONTENTS AND DATAFILES CASCADE CONSTRAINTS',
             'DROP TABLESPACE %(tblspace_temp)s INCLUDING CONTENTS AND DATAFILES CASCADE CONSTRAINTS',
-            ]
+        ]
         self._execute_statements(cursor, statements, parameters, verbosity)
 
     def _destroy_test_user(self, cursor, parameters, verbosity):
diff --git a/django/db/backends/oracle/introspection.py b/django/db/backends/oracle/introspection.py
index 361308a62cb1b..a2fad92509268 100644
--- a/django/db/backends/oracle/introspection.py
+++ b/django/db/backends/oracle/introspection.py
@@ -1,10 +1,13 @@
+import re
+
+import cx_Oracle
+
 from django.db.backends import BaseDatabaseIntrospection, FieldInfo
 from django.utils.encoding import force_text
-import cx_Oracle
-import re
 
 foreign_key_re = re.compile(r"\sCONSTRAINT `[^`]*` FOREIGN KEY \(`([^`]*)`\) REFERENCES `([^`]*)` \(`([^`]*)`\)")
 
+
 class DatabaseIntrospection(BaseDatabaseIntrospection):
     # Maps type objects to Django Field types.
     data_types_reverse = {
@@ -95,11 +98,11 @@ def get_key_columns(self, cursor, table_name):
             SELECT ccol.column_name, rcol.table_name AS referenced_table, rcol.column_name AS referenced_column
             FROM user_constraints c
             JOIN user_cons_columns ccol
-              ON ccol.constraint_name = c.constraint_name 
+              ON ccol.constraint_name = c.constraint_name
             JOIN user_cons_columns rcol
-              ON rcol.constraint_name = c.r_constraint_name 
-            WHERE c.table_name = %s AND c.constraint_type = 'R'""" , [table_name.upper()])
-        return [tuple(cell.lower() for cell in row) 
+              ON rcol.constraint_name = c.r_constraint_name
+            WHERE c.table_name = %s AND c.constraint_type = 'R'""", [table_name.upper()])
+        return [tuple(cell.lower() for cell in row)
                 for row in cursor.fetchall()]
 
     def get_indexes(self, cursor, table_name):
diff --git a/django/db/backends/postgresql_psycopg2/base.py b/django/db/backends/postgresql_psycopg2/base.py
index 6ed2cfcc7cdc7..e6760655782da 100644
--- a/django/db/backends/postgresql_psycopg2/base.py
+++ b/django/db/backends/postgresql_psycopg2/base.py
@@ -6,7 +6,9 @@
 import logging
 import sys
 
-from django.db.backends import *
+from django.conf import settings
+from django.db.backends import (BaseDatabaseFeatures, BaseDatabaseWrapper,
+    BaseDatabaseValidation)
 from django.db.backends.postgresql_psycopg2.operations import DatabaseOperations
 from django.db.backends.postgresql_psycopg2.client import DatabaseClient
 from django.db.backends.postgresql_psycopg2.creation import DatabaseCreation
@@ -33,11 +35,13 @@
 
 logger = logging.getLogger('django.db.backends')
 
+
 def utc_tzinfo_factory(offset):
     if offset != 0:
         raise AssertionError("database connection isn't set to UTC")
     return utc
 
+
 class DatabaseFeatures(BaseDatabaseFeatures):
     needs_datetime_string_cast = False
     can_return_id_from_insert = True
@@ -52,6 +56,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     supports_transactions = True
     can_distinct_on_fields = True
 
+
 class DatabaseWrapper(BaseDatabaseWrapper):
     vendor = 'postgresql'
     operators = {
@@ -132,7 +137,8 @@ def init_connection_state(self):
                 # Set the time zone in autocommit mode (see #17062)
                 self.set_autocommit(True)
                 self.connection.cursor().execute(
-                        self.ops.set_time_zone_sql(), [tz])
+                    self.ops.set_time_zone_sql(), [tz]
+                )
         self.connection.set_isolation_level(self.isolation_level)
 
     def create_cursor(self):
diff --git a/django/db/backends/postgresql_psycopg2/client.py b/django/db/backends/postgresql_psycopg2/client.py
index a5c02969ea8b3..23ac9f2975dcf 100644
--- a/django/db/backends/postgresql_psycopg2/client.py
+++ b/django/db/backends/postgresql_psycopg2/client.py
@@ -3,6 +3,7 @@
 
 from django.db.backends import BaseDatabaseClient
 
+
 class DatabaseClient(BaseDatabaseClient):
     executable_name = 'psql'
 
@@ -20,4 +21,3 @@ def runshell(self):
             sys.exit(os.system(" ".join(args)))
         else:
             os.execvp(self.executable_name, args)
-
diff --git a/django/db/backends/postgresql_psycopg2/creation.py b/django/db/backends/postgresql_psycopg2/creation.py
index d4260e05c4ad8..cbf901555d528 100644
--- a/django/db/backends/postgresql_psycopg2/creation.py
+++ b/django/db/backends/postgresql_psycopg2/creation.py
@@ -8,29 +8,29 @@ class DatabaseCreation(BaseDatabaseCreation):
     # be interpolated against the values of Field.__dict__ before being output.
     # If a column type is set to None, it won't be included in the output.
     data_types = {
-        'AutoField':         'serial',
-        'BinaryField':       'bytea',
-        'BooleanField':      'boolean',
-        'CharField':         'varchar(%(max_length)s)',
+        'AutoField': 'serial',
+        'BinaryField': 'bytea',
+        'BooleanField': 'boolean',
+        'CharField': 'varchar(%(max_length)s)',
         'CommaSeparatedIntegerField': 'varchar(%(max_length)s)',
-        'DateField':         'date',
-        'DateTimeField':     'timestamp with time zone',
-        'DecimalField':      'numeric(%(max_digits)s, %(decimal_places)s)',
-        'FileField':         'varchar(%(max_length)s)',
-        'FilePathField':     'varchar(%(max_length)s)',
-        'FloatField':        'double precision',
-        'IntegerField':      'integer',
-        'BigIntegerField':   'bigint',
-        'IPAddressField':    'inet',
+        'DateField': 'date',
+        'DateTimeField': 'timestamp with time zone',
+        'DecimalField': 'numeric(%(max_digits)s, %(decimal_places)s)',
+        'FileField': 'varchar(%(max_length)s)',
+        'FilePathField': 'varchar(%(max_length)s)',
+        'FloatField': 'double precision',
+        'IntegerField': 'integer',
+        'BigIntegerField': 'bigint',
+        'IPAddressField': 'inet',
         'GenericIPAddressField': 'inet',
-        'NullBooleanField':  'boolean',
-        'OneToOneField':     'integer',
+        'NullBooleanField': 'boolean',
+        'OneToOneField': 'integer',
         'PositiveIntegerField': 'integer CHECK ("%(column)s" >= 0)',
         'PositiveSmallIntegerField': 'smallint CHECK ("%(column)s" >= 0)',
-        'SlugField':         'varchar(%(max_length)s)',
+        'SlugField': 'varchar(%(max_length)s)',
         'SmallIntegerField': 'smallint',
-        'TextField':         'text',
-        'TimeField':         'time',
+        'TextField': 'text',
+        'TimeField': 'time',
     }
 
     def sql_table_creation_suffix(self):
@@ -54,7 +54,7 @@ def sql_indexes_for_field(self, model, f, style):
 
             def get_index_sql(index_name, opclass=''):
                 return (style.SQL_KEYWORD('CREATE INDEX') + ' ' +
-                        style.SQL_TABLE(qn(truncate_name(index_name,self.connection.ops.max_name_length()))) + ' ' +
+                        style.SQL_TABLE(qn(truncate_name(index_name, self.connection.ops.max_name_length()))) + ' ' +
                         style.SQL_KEYWORD('ON') + ' ' +
                         style.SQL_TABLE(qn(db_table)) + ' ' +
                         "(%s%s)" % (style.SQL_FIELD(qn(f.column)), opclass) +
diff --git a/django/db/backends/postgresql_psycopg2/introspection.py b/django/db/backends/postgresql_psycopg2/introspection.py
index c334b9d6d0b0e..0ebd3c1ed5710 100644
--- a/django/db/backends/postgresql_psycopg2/introspection.py
+++ b/django/db/backends/postgresql_psycopg2/introspection.py
@@ -25,7 +25,7 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
         1266: 'TimeField',
         1700: 'DecimalField',
     }
-        
+
     def get_table_list(self, cursor):
         "Returns a list of table names in the current database."
         cursor.execute("""
@@ -47,7 +47,7 @@ def get_table_description(self, cursor, table_name):
             WHERE table_name = %s""", [table_name])
         null_map = dict(cursor.fetchall())
         cursor.execute("SELECT * FROM %s LIMIT 1" % self.connection.ops.quote_name(table_name))
-        return [FieldInfo(*((force_text(line[0]),) + line[1:6] + (null_map[force_text(line[0])]=='YES',)))
+        return [FieldInfo(*((force_text(line[0]),) + line[1:6] + (null_map[force_text(line[0])] == 'YES',)))
                 for line in cursor.description]
 
     def get_relations(self, cursor, table_name):
@@ -81,7 +81,7 @@ def get_key_columns(self, cursor, table_name):
                 ON ccu.constraint_catalog = tc.constraint_catalog
                     AND ccu.constraint_schema = tc.constraint_schema
                     AND ccu.constraint_name = tc.constraint_name
-            WHERE kcu.table_name = %s AND tc.constraint_type = 'FOREIGN KEY'""" , [table_name])
+            WHERE kcu.table_name = %s AND tc.constraint_type = 'FOREIGN KEY'""", [table_name])
         key_columns.extend(cursor.fetchall())
         return key_columns
 
diff --git a/django/db/backends/postgresql_psycopg2/operations.py b/django/db/backends/postgresql_psycopg2/operations.py
index c5aab8469307d..cc78ffe4491b6 100644
--- a/django/db/backends/postgresql_psycopg2/operations.py
+++ b/django/db/backends/postgresql_psycopg2/operations.py
@@ -135,7 +135,7 @@ def sequence_reset_by_name_sql(self, style, sequences):
                 # This will be the case if it's an m2m using an autogenerated
                 # intermediate table (see BaseDatabaseIntrospection.sequence_list)
                 column_name = 'id'
-            sql.append("%s setval(pg_get_serial_sequence('%s','%s'), 1, false);" % \
+            sql.append("%s setval(pg_get_serial_sequence('%s','%s'), 1, false);" %
                 (style.SQL_KEYWORD('SELECT'),
                 style.SQL_TABLE(self.quote_name(table_name)),
                 style.SQL_FIELD(column_name))
@@ -161,7 +161,7 @@ def sequence_reset_sql(self, style, model_list):
 
             for f in model._meta.local_fields:
                 if isinstance(f, models.AutoField):
-                    output.append("%s setval(pg_get_serial_sequence('%s','%s'), coalesce(max(%s), 1), max(%s) %s null) %s %s;" % \
+                    output.append("%s setval(pg_get_serial_sequence('%s','%s'), coalesce(max(%s), 1), max(%s) %s null) %s %s;" %
                         (style.SQL_KEYWORD('SELECT'),
                         style.SQL_TABLE(qn(model._meta.db_table)),
                         style.SQL_FIELD(f.column),
@@ -173,7 +173,7 @@ def sequence_reset_sql(self, style, model_list):
                     break # Only one AutoField is allowed per model, so don't bother continuing.
             for f in model._meta.many_to_many:
                 if not f.rel.through:
-                    output.append("%s setval(pg_get_serial_sequence('%s','%s'), coalesce(max(%s), 1), max(%s) %s null) %s %s;" % \
+                    output.append("%s setval(pg_get_serial_sequence('%s','%s'), coalesce(max(%s), 1), max(%s) %s null) %s %s;" %
                         (style.SQL_KEYWORD('SELECT'),
                         style.SQL_TABLE(qn(f.m2m_db_table())),
                         style.SQL_FIELD('id'),
diff --git a/django/db/backends/postgresql_psycopg2/version.py b/django/db/backends/postgresql_psycopg2/version.py
index 8ef516704eaa1..dae94f2dacd44 100644
--- a/django/db/backends/postgresql_psycopg2/version.py
+++ b/django/db/backends/postgresql_psycopg2/version.py
@@ -19,7 +19,8 @@ def _parse_version(text):
     try:
         return int(major) * 10000 + int(major2) * 100 + int(minor)
     except (ValueError, TypeError):
-        return int(major) * 10000 +  int(major2) * 100
+        return int(major) * 10000 + int(major2) * 100
+
 
 def get_version(connection):
     """
diff --git a/django/db/backends/sqlite3/base.py b/django/db/backends/sqlite3/base.py
index 4345790b06cee..dc7db2fceb08b 100644
--- a/django/db/backends/sqlite3/base.py
+++ b/django/db/backends/sqlite3/base.py
@@ -11,8 +11,10 @@
 import warnings
 import re
 
+from django.conf import settings
 from django.db import utils
-from django.db.backends import *
+from django.db.backends import (util, BaseDatabaseFeatures,
+    BaseDatabaseOperations, BaseDatabaseWrapper, BaseDatabaseValidation)
 from django.db.backends.sqlite3.client import DatabaseClient
 from django.db.backends.sqlite3.creation import DatabaseCreation
 from django.db.backends.sqlite3.introspection import DatabaseIntrospection
@@ -42,6 +44,7 @@
 DatabaseError = Database.DatabaseError
 IntegrityError = Database.IntegrityError
 
+
 def parse_datetime_with_timezone_support(value):
     dt = parse_datetime(value)
     # Confirm that dt is naive before overwriting its tzinfo.
@@ -49,6 +52,7 @@ def parse_datetime_with_timezone_support(value):
         dt = dt.replace(tzinfo=timezone.utc)
     return dt
 
+
 def adapt_datetime_with_timezone_support(value):
     # Equivalent to DateTimeField.get_db_prep_value. Used only by raw SQL.
     if settings.USE_TZ:
@@ -61,6 +65,7 @@ def adapt_datetime_with_timezone_support(value):
         value = value.astimezone(timezone.utc).replace(tzinfo=None)
     return value.isoformat(str(" "))
 
+
 def decoder(conv_func):
     """ The Python sqlite3 interface returns always byte strings.
         This function converts the received value to a regular string before
@@ -81,6 +86,7 @@ def decoder(conv_func):
 Database.register_adapter(str, lambda s: s.decode('utf-8'))
 Database.register_adapter(SafeBytes, lambda s: s.decode('utf-8'))
 
+
 class DatabaseFeatures(BaseDatabaseFeatures):
     # SQLite cannot handle us only partially reading from a cursor's result set
     # and then writing the same rows to the database in another cursor. This
@@ -124,6 +130,7 @@ def supports_stddev(self):
     def has_zoneinfo_database(self):
         return pytz is not None
 
+
 class DatabaseOperations(BaseDatabaseOperations):
     def bulk_batch_size(self, fields, objs):
         """
@@ -272,6 +279,7 @@ def bulk_insert_sql(self, fields, num_values):
         res.extend(["UNION ALL SELECT %s" % ", ".join(["%s"] * len(fields))] * (num_values - 1))
         return " ".join(res)
 
+
 class DatabaseWrapper(BaseDatabaseWrapper):
     vendor = 'sqlite'
     # SQLite requires LIKE statements to include an ESCAPE clause if the value
@@ -426,6 +434,7 @@ def _start_transaction_under_autocommit(self):
 
 FORMAT_QMARK_REGEX = re.compile(r'(?<!%)%s')
 
+
 class SQLiteCursorWrapper(Database.Cursor):
     """
     Django uses "format" style placeholders, but pysqlite2 uses "qmark" style.
@@ -445,6 +454,7 @@ def executemany(self, query, param_list):
     def convert_query(self, query):
         return FORMAT_QMARK_REGEX.sub('?', query).replace('%%', '%')
 
+
 def _sqlite_date_extract(lookup_type, dt):
     if dt is None:
         return None
@@ -457,6 +467,7 @@ def _sqlite_date_extract(lookup_type, dt):
     else:
         return getattr(dt, lookup_type)
 
+
 def _sqlite_date_trunc(lookup_type, dt):
     try:
         dt = util.typecast_timestamp(dt)
@@ -469,6 +480,7 @@ def _sqlite_date_trunc(lookup_type, dt):
     elif lookup_type == 'day':
         return "%i-%02i-%02i" % (dt.year, dt.month, dt.day)
 
+
 def _sqlite_datetime_extract(lookup_type, dt, tzname):
     if dt is None:
         return None
@@ -483,6 +495,7 @@ def _sqlite_datetime_extract(lookup_type, dt, tzname):
     else:
         return getattr(dt, lookup_type)
 
+
 def _sqlite_datetime_trunc(lookup_type, dt, tzname):
     try:
         dt = util.typecast_timestamp(dt)
@@ -503,6 +516,7 @@ def _sqlite_datetime_trunc(lookup_type, dt, tzname):
     elif lookup_type == 'second':
         return "%i-%02i-%02i %02i:%02i:%02i" % (dt.year, dt.month, dt.day, dt.hour, dt.minute, dt.second)
 
+
 def _sqlite_format_dtdelta(dt, conn, days, secs, usecs):
     try:
         dt = util.typecast_timestamp(dt)
@@ -517,5 +531,6 @@ def _sqlite_format_dtdelta(dt, conn, days, secs, usecs):
     # It will be formatted as "%Y-%m-%d" or "%Y-%m-%d %H:%M:%S[.%f]"
     return str(dt)
 
+
 def _sqlite_regexp(re_pattern, re_string):
     return bool(re.search(re_pattern, force_text(re_string))) if re_string is not None else False
diff --git a/django/db/backends/sqlite3/client.py b/django/db/backends/sqlite3/client.py
index 5b5b7326f223b..6a3ad9e76fba2 100644
--- a/django/db/backends/sqlite3/client.py
+++ b/django/db/backends/sqlite3/client.py
@@ -3,6 +3,7 @@
 
 from django.db.backends import BaseDatabaseClient
 
+
 class DatabaseClient(BaseDatabaseClient):
     executable_name = 'sqlite3'
 
@@ -13,4 +14,3 @@ def runshell(self):
             sys.exit(os.system(" ".join(args)))
         else:
             os.execvp(self.executable_name, args)
-
diff --git a/django/db/backends/sqlite3/creation.py b/django/db/backends/sqlite3/creation.py
index a9fb273f7ad22..435cee3436f90 100644
--- a/django/db/backends/sqlite3/creation.py
+++ b/django/db/backends/sqlite3/creation.py
@@ -1,36 +1,38 @@
 import os
 import sys
+
 from django.db.backends.creation import BaseDatabaseCreation
 from django.utils.six.moves import input
 
+
 class DatabaseCreation(BaseDatabaseCreation):
     # SQLite doesn't actually support most of these types, but it "does the right
     # thing" given more verbose field definitions, so leave them as is so that
     # schema inspection is more useful.
     data_types = {
-        'AutoField':                    'integer',
-        'BinaryField':                  'BLOB',
-        'BooleanField':                 'bool',
-        'CharField':                    'varchar(%(max_length)s)',
-        'CommaSeparatedIntegerField':   'varchar(%(max_length)s)',
-        'DateField':                    'date',
-        'DateTimeField':                'datetime',
-        'DecimalField':                 'decimal',
-        'FileField':                    'varchar(%(max_length)s)',
-        'FilePathField':                'varchar(%(max_length)s)',
-        'FloatField':                   'real',
-        'IntegerField':                 'integer',
-        'BigIntegerField':              'bigint',
-        'IPAddressField':               'char(15)',
-        'GenericIPAddressField':        'char(39)',
-        'NullBooleanField':             'bool',
-        'OneToOneField':                'integer',
-        'PositiveIntegerField':         'integer unsigned',
-        'PositiveSmallIntegerField':    'smallint unsigned',
-        'SlugField':                    'varchar(%(max_length)s)',
-        'SmallIntegerField':            'smallint',
-        'TextField':                    'text',
-        'TimeField':                    'time',
+        'AutoField': 'integer',
+        'BinaryField': 'BLOB',
+        'BooleanField': 'bool',
+        'CharField': 'varchar(%(max_length)s)',
+        'CommaSeparatedIntegerField': 'varchar(%(max_length)s)',
+        'DateField': 'date',
+        'DateTimeField': 'datetime',
+        'DecimalField': 'decimal',
+        'FileField': 'varchar(%(max_length)s)',
+        'FilePathField': 'varchar(%(max_length)s)',
+        'FloatField': 'real',
+        'IntegerField': 'integer',
+        'BigIntegerField': 'bigint',
+        'IPAddressField': 'char(15)',
+        'GenericIPAddressField': 'char(39)',
+        'NullBooleanField': 'bool',
+        'OneToOneField': 'integer',
+        'PositiveIntegerField': 'integer unsigned',
+        'PositiveSmallIntegerField': 'smallint unsigned',
+        'SlugField': 'varchar(%(max_length)s)',
+        'SmallIntegerField': 'smallint',
+        'TextField': 'text',
+        'TimeField': 'time',
     }
 
     def sql_for_pending_references(self, model, style, pending_references):
@@ -80,7 +82,6 @@ def test_db_signature(self):
         SQLite since the databases will be distinct despite having the same
         TEST_NAME. See http://www.sqlite.org/inmemorydb.html
         """
-        settings_dict = self.connection.settings_dict
         test_dbname = self._get_test_db_name()
         sig = [self.connection.settings_dict['NAME']]
         if test_dbname == ':memory:':
diff --git a/django/db/backends/sqlite3/introspection.py b/django/db/backends/sqlite3/introspection.py
index 431e112e568c3..385888ed40b75 100644
--- a/django/db/backends/sqlite3/introspection.py
+++ b/django/db/backends/sqlite3/introspection.py
@@ -1,8 +1,11 @@
 import re
+
 from django.db.backends import BaseDatabaseIntrospection, FieldInfo
 
+
 field_size_re = re.compile(r'^\s*(?:var)?char\s*\(\s*(\d+)\s*\)\s*$')
 
+
 def get_field_size(name):
     """ Extract the size number from a "varchar(11)" type name """
     m = field_size_re.search(name)
@@ -46,6 +49,7 @@ def __getitem__(self, key):
                 return ('CharField', {'max_length': size})
             raise KeyError
 
+
 class DatabaseIntrospection(BaseDatabaseIntrospection):
     data_types_reverse = FlexibleFieldLookupDict()
 
@@ -76,7 +80,7 @@ def get_relations(self, cursor, table_name):
         # Schema for this table
         cursor.execute("SELECT sql FROM sqlite_master WHERE tbl_name = %s AND type = %s", [table_name, "table"])
         results = cursor.fetchone()[0].strip()
-        results = results[results.index('(')+1:results.rindex(')')]
+        results = results[results.index('(') + 1:results.rindex(')')]
 
         # Walk through and look for references to other tables. SQLite doesn't
         # really have enforced references, but since it echoes out the SQL used
@@ -96,8 +100,7 @@ def get_relations(self, cursor, table_name):
             result = cursor.fetchall()[0]
             other_table_results = result[0].strip()
             li, ri = other_table_results.index('('), other_table_results.rindex(')')
-            other_table_results = other_table_results[li+1:ri]
-
+            other_table_results = other_table_results[li + 1:ri]
 
             for other_index, other_desc in enumerate(other_table_results.split(',')):
                 other_desc = other_desc.strip()
@@ -121,7 +124,7 @@ def get_key_columns(self, cursor, table_name):
         # Schema for this table
         cursor.execute("SELECT sql FROM sqlite_master WHERE tbl_name = %s AND type = %s", [table_name, "table"])
         results = cursor.fetchone()[0].strip()
-        results = results[results.index('(')+1:results.rindex(')')]
+        results = results[results.index('(') + 1:results.rindex(')')]
 
         # Walk through and look for references to other tables. SQLite doesn't
         # really have enforced references, but since it echoes out the SQL used
@@ -166,7 +169,7 @@ def get_primary_key_column(self, cursor, table_name):
         # Don't use PRAGMA because that causes issues with some transactions
         cursor.execute("SELECT sql FROM sqlite_master WHERE tbl_name = %s AND type = %s", [table_name, "table"])
         results = cursor.fetchone()[0].strip()
-        results = results[results.index('(')+1:results.rindex(')')]
+        results = results[results.index('(') + 1:results.rindex(')')]
         for field_desc in results.split(','):
             field_desc = field_desc.strip()
             m = re.search('"(.*)".*PRIMARY KEY$', field_desc)
diff --git a/django/db/backends/util.py b/django/db/backends/util.py
index aa2601277a766..f8157c50e7726 100644
--- a/django/db/backends/util.py
+++ b/django/db/backends/util.py
@@ -85,20 +85,25 @@ def executemany(self, sql, param_list):
 def typecast_date(s):
     return datetime.date(*map(int, s.split('-'))) if s else None # returns None if s is null
 
+
 def typecast_time(s): # does NOT store time zone information
-    if not s: return None
+    if not s:
+        return None
     hour, minutes, seconds = s.split(':')
     if '.' in seconds: # check whether seconds have a fractional part
         seconds, microseconds = seconds.split('.')
     else:
         microseconds = '0'
-    return datetime.time(int(hour), int(minutes), int(seconds), int(float('.'+microseconds) * 1000000))
+    return datetime.time(int(hour), int(minutes), int(seconds), int(float('.' + microseconds) * 1000000))
+
 
 def typecast_timestamp(s): # does NOT store time zone information
     # "2005-07-29 15:48:00.590358-05"
     # "2005-07-29 09:56:00-05"
-    if not s: return None
-    if not ' ' in s: return typecast_date(s)
+    if not s:
+        return None
+    if not ' ' in s:
+        return typecast_date(s)
     d, t = s.split()
     # Extract timezone information, if it exists. Currently we just throw
     # it away, but in the future we may make use of it.
@@ -122,11 +127,13 @@ def typecast_timestamp(s): # does NOT store time zone information
         int(times[0]), int(times[1]), int(seconds),
         int((microseconds + '000000')[:6]), tzinfo)
 
+
 def typecast_decimal(s):
     if s is None or s == '':
         return None
     return decimal.Decimal(s)
 
+
 ###############################################
 # Converters from Python to database (string) #
 ###############################################
@@ -136,6 +143,7 @@ def rev_typecast_decimal(d):
         return None
     return str(d)
 
+
 def truncate_name(name, length=None, hash_len=4):
     """Shortens a string to a repeatable mangled version with the given length.
     """
@@ -143,7 +151,8 @@ def truncate_name(name, length=None, hash_len=4):
         return name
 
     hsh = hashlib.md5(force_bytes(name)).hexdigest()[:hash_len]
-    return '%s%s' % (name[:length-hash_len], hsh)
+    return '%s%s' % (name[:length - hash_len], hsh)
+
 
 def format_number(value, max_digits, decimal_places):
     """
diff --git a/django/db/models/__init__.py b/django/db/models/__init__.py
index b5dd1a58bc5f3..4d310e480b059 100644
--- a/django/db/models/__init__.py
+++ b/django/db/models/__init__.py
@@ -26,6 +26,7 @@ def permalink(func):
         (viewname, viewargs, viewkwargs)
     """
     from django.core.urlresolvers import reverse
+
     @wraps(func)
     def inner(*args, **kwargs):
         bits = func(*args, **kwargs)
diff --git a/django/db/models/aggregates.py b/django/db/models/aggregates.py
index b89db1c5632e6..1db3890204088 100644
--- a/django/db/models/aggregates.py
+++ b/django/db/models/aggregates.py
@@ -3,6 +3,7 @@
 """
 from django.db.models.constants import LOOKUP_SEP
 
+
 def refs_aggregate(lookup_parts, aggregates):
     """
     A little helper method to check if the lookup_parts contains references
@@ -15,6 +16,7 @@ def refs_aggregate(lookup_parts, aggregates):
             return True
     return False
 
+
 class Aggregate(object):
     """
     Default Aggregate definition.
@@ -58,23 +60,30 @@ def add_to_query(self, query, alias, col, source, is_summary):
         aggregate = klass(col, source=source, is_summary=is_summary, **self.extra)
         query.aggregates[alias] = aggregate
 
+
 class Avg(Aggregate):
     name = 'Avg'
 
+
 class Count(Aggregate):
     name = 'Count'
 
+
 class Max(Aggregate):
     name = 'Max'
 
+
 class Min(Aggregate):
     name = 'Min'
 
+
 class StdDev(Aggregate):
     name = 'StdDev'
 
+
 class Sum(Aggregate):
     name = 'Sum'
 
+
 class Variance(Aggregate):
     name = 'Variance'
diff --git a/django/db/models/base.py b/django/db/models/base.py
index 1238bfb4cee3d..fbfda616a130e 100644
--- a/django/db/models/base.py
+++ b/django/db/models/base.py
@@ -226,9 +226,9 @@ def __new__(cls, name, bases, attrs):
             # class
             for field in base._meta.virtual_fields:
                 if base._meta.abstract and field.name in field_names:
-                    raise FieldError('Local field %r in class %r clashes '\
-                                     'with field of similar name from '\
-                                     'abstract base class %r' % \
+                    raise FieldError('Local field %r in class %r clashes '
+                                     'with field of similar name from '
+                                     'abstract base class %r' %
                                         (field.name, name, base.__name__))
                 new_class.add_to_class(field.name, copy.deepcopy(field))
 
@@ -1008,8 +1008,6 @@ def get_absolute_url(opts, func, self, *args, **kwargs):
 # MISC #
 ########
 
-class Empty(object):
-    pass
 
 def simple_class_factory(model, attrs):
     """
@@ -1017,6 +1015,7 @@ def simple_class_factory(model, attrs):
     """
     return model
 
+
 def model_unpickle(model_id, attrs, factory):
     """
     Used to unpickle Model subclasses with deferred fields.
diff --git a/django/db/models/expressions.py b/django/db/models/expressions.py
index 6e0f3c434e05c..b4eea5fe71a12 100644
--- a/django/db/models/expressions.py
+++ b/django/db/models/expressions.py
@@ -4,6 +4,7 @@
 from django.db.models.constants import LOOKUP_SEP
 from django.utils import tree
 
+
 class ExpressionNode(tree.Node):
     """
     Base class for all query expressions.
@@ -128,6 +129,7 @@ def __ror__(self, other):
             "Use .bitand() and .bitor() for bitwise logical operations."
         )
 
+
 class F(ExpressionNode):
     """
     An expression representing the value of the given field.
@@ -147,6 +149,7 @@ def prepare(self, evaluator, query, allow_joins):
     def evaluate(self, evaluator, qn, connection):
         return evaluator.evaluate_leaf(self, qn, connection)
 
+
 class DateModifierNode(ExpressionNode):
     """
     Node that implements the following syntax:
diff --git a/django/db/models/fields/__init__.py b/django/db/models/fields/__init__.py
index a12b150cf6d1a..02d887b7f8a97 100644
--- a/django/db/models/fields/__init__.py
+++ b/django/db/models/fields/__init__.py
@@ -25,9 +25,11 @@
 from django.utils.ipv6 import clean_ipv6_address
 from django.utils import six
 
+
 class Empty(object):
     pass
 
+
 class NOT_PROVIDED:
     pass
 
@@ -35,12 +37,15 @@ class NOT_PROVIDED:
 # of most "choices" lists.
 BLANK_CHOICE_DASH = [("", "---------")]
 
+
 def _load_field(app_label, model_name, field_name):
     return get_model(app_label, model_name)._meta.get_field_by_name(field_name)[0]
 
+
 class FieldDoesNotExist(Exception):
     pass
 
+
 # A guide to Field parameters:
 #
 #   * name:      The name of the field specifed in the model.
@@ -61,6 +66,7 @@ def _empty(of_cls):
     new.__class__ = of_cls
     return new
 
+
 @total_ordering
 class Field(object):
     """Base class for all field types"""
@@ -444,12 +450,12 @@ def get_prep_lookup(self, lookup_type, value):
         if hasattr(value, '_prepare'):
             return value._prepare()
 
-        if lookup_type in (
-                'iexact', 'contains', 'icontains',
-                'startswith', 'istartswith', 'endswith', 'iendswith',
-                'month', 'day', 'week_day', 'hour', 'minute', 'second',
-                'isnull', 'search', 'regex', 'iregex',
-            ):
+        if lookup_type in {
+            'iexact', 'contains', 'icontains',
+            'startswith', 'istartswith', 'endswith', 'iendswith',
+            'month', 'day', 'week_day', 'hour', 'minute', 'second',
+            'isnull', 'search', 'regex', 'iregex',
+        }:
             return value
         elif lookup_type in ('exact', 'gt', 'gte', 'lt', 'lte'):
             return self.get_prep_value(value)
@@ -593,7 +599,7 @@ def _get_flatchoices(self):
             if isinstance(value, (list, tuple)):
                 flat.extend(value)
             else:
-                flat.append((choice,value))
+                flat.append((choice, value))
         return flat
     flatchoices = property(_get_flatchoices)
 
@@ -712,6 +718,7 @@ def contribute_to_class(self, cls, name):
     def formfield(self, **kwargs):
         return None
 
+
 class BooleanField(Field):
     empty_strings_allowed = False
     default_error_messages = {
@@ -766,13 +773,13 @@ def formfield(self, **kwargs):
         if self.choices:
             include_blank = (self.null or
                              not (self.has_default() or 'initial' in kwargs))
-            defaults = {'choices': self.get_choices(
-                                       include_blank=include_blank)}
+            defaults = {'choices': self.get_choices(include_blank=include_blank)}
         else:
             defaults = {'form_class': forms.BooleanField}
         defaults.update(kwargs)
         return super(BooleanField, self).formfield(**defaults)
 
+
 class CharField(Field):
     description = _("String (up to %(max_length)s)")
 
@@ -799,6 +806,7 @@ def formfield(self, **kwargs):
         defaults.update(kwargs)
         return super(CharField, self).formfield(**defaults)
 
+
 # TODO: Maybe move this into contrib, because it's specialized.
 class CommaSeparatedIntegerField(CharField):
     default_validators = [validators.validate_comma_separated_integer_list]
@@ -813,6 +821,7 @@ def formfield(self, **kwargs):
         defaults.update(kwargs)
         return super(CommaSeparatedIntegerField, self).formfield(**defaults)
 
+
 class DateField(Field):
     empty_strings_allowed = False
     default_error_messages = {
@@ -885,7 +894,7 @@ def pre_save(self, model_instance, add):
             return super(DateField, self).pre_save(model_instance, add)
 
     def contribute_to_class(self, cls, name):
-        super(DateField,self).contribute_to_class(cls, name)
+        super(DateField, self).contribute_to_class(cls, name)
         if not self.null:
             setattr(cls, 'get_next_by_%s' % self.name,
                 curry(cls._get_next_or_previous_by_FIELD, field=self,
@@ -919,6 +928,7 @@ def formfield(self, **kwargs):
         defaults.update(kwargs)
         return super(DateField, self).formfield(**defaults)
 
+
 class DateTimeField(DateField):
     empty_strings_allowed = False
     default_error_messages = {
@@ -1025,6 +1035,7 @@ def formfield(self, **kwargs):
         defaults.update(kwargs)
         return super(DateTimeField, self).formfield(**defaults)
 
+
 class DecimalField(Field):
     empty_strings_allowed = False
     default_error_messages = {
@@ -1096,6 +1107,7 @@ def formfield(self, **kwargs):
         defaults.update(kwargs)
         return super(DecimalField, self).formfield(**defaults)
 
+
 class EmailField(CharField):
     default_validators = [validators.validate_email]
     description = _("Email address")
@@ -1122,13 +1134,14 @@ def formfield(self, **kwargs):
         defaults.update(kwargs)
         return super(EmailField, self).formfield(**defaults)
 
+
 class FilePathField(Field):
     description = _("File path")
 
     def __init__(self, verbose_name=None, name=None, path='', match=None,
                  recursive=False, allow_files=True, allow_folders=False, **kwargs):
         self.path, self.match, self.recursive = path, match, recursive
-        self.allow_files, self.allow_folders =  allow_files, allow_folders
+        self.allow_files, self.allow_folders = allow_files, allow_folders
         kwargs['max_length'] = kwargs.get('max_length', 100)
         Field.__init__(self, verbose_name, name, **kwargs)
 
@@ -1163,6 +1176,7 @@ def formfield(self, **kwargs):
     def get_internal_type(self):
         return "FilePathField"
 
+
 class FloatField(Field):
     empty_strings_allowed = False
     default_error_messages = {
@@ -1195,6 +1209,7 @@ def formfield(self, **kwargs):
         defaults.update(kwargs)
         return super(FloatField, self).formfield(**defaults)
 
+
 class IntegerField(Field):
     empty_strings_allowed = False
     default_error_messages = {
@@ -1233,6 +1248,7 @@ def formfield(self, **kwargs):
         defaults.update(kwargs)
         return super(IntegerField, self).formfield(**defaults)
 
+
 class BigIntegerField(IntegerField):
     empty_strings_allowed = False
     description = _("Big (8 byte) integer")
@@ -1247,6 +1263,7 @@ def formfield(self, **kwargs):
         defaults.update(kwargs)
         return super(BigIntegerField, self).formfield(**defaults)
 
+
 class IPAddressField(Field):
     empty_strings_allowed = False
     description = _("IPv4 address")
@@ -1268,6 +1285,7 @@ def formfield(self, **kwargs):
         defaults.update(kwargs)
         return super(IPAddressField, self).formfield(**defaults)
 
+
 class GenericIPAddressField(Field):
     empty_strings_allowed = True
     description = _("IP address")
@@ -1383,6 +1401,7 @@ def formfield(self, **kwargs):
         defaults.update(kwargs)
         return super(NullBooleanField, self).formfield(**defaults)
 
+
 class PositiveIntegerField(IntegerField):
     description = _("Positive integer")
 
@@ -1394,6 +1413,7 @@ def formfield(self, **kwargs):
         defaults.update(kwargs)
         return super(PositiveIntegerField, self).formfield(**defaults)
 
+
 class PositiveSmallIntegerField(IntegerField):
     description = _("Positive small integer")
 
@@ -1405,6 +1425,7 @@ def formfield(self, **kwargs):
         defaults.update(kwargs)
         return super(PositiveSmallIntegerField, self).formfield(**defaults)
 
+
 class SlugField(CharField):
     default_validators = [validators.validate_slug]
     description = _("Slug (up to %(max_length)s)")
@@ -1434,12 +1455,14 @@ def formfield(self, **kwargs):
         defaults.update(kwargs)
         return super(SlugField, self).formfield(**defaults)
 
+
 class SmallIntegerField(IntegerField):
     description = _("Small integer")
 
     def get_internal_type(self):
         return "SmallIntegerField"
 
+
 class TextField(Field):
     description = _("Text")
 
@@ -1456,6 +1479,7 @@ def formfield(self, **kwargs):
         defaults.update(kwargs)
         return super(TextField, self).formfield(**defaults)
 
+
 class TimeField(Field):
     empty_strings_allowed = False
     default_error_messages = {
@@ -1539,6 +1563,7 @@ def formfield(self, **kwargs):
         defaults.update(kwargs)
         return super(TimeField, self).formfield(**defaults)
 
+
 class URLField(CharField):
     default_validators = [validators.URLValidator()]
     description = _("URL")
@@ -1562,6 +1587,7 @@ def formfield(self, **kwargs):
         defaults.update(kwargs)
         return super(URLField, self).formfield(**defaults)
 
+
 class BinaryField(Field):
     description = _("Raw binary data")
     empty_values = [None, b'']
diff --git a/django/db/models/fields/files.py b/django/db/models/fields/files.py
index 7663c8ab90095..311f74a905ba6 100644
--- a/django/db/models/fields/files.py
+++ b/django/db/models/fields/files.py
@@ -11,6 +11,7 @@
 from django.utils import six
 from django.utils.translation import ugettext_lazy as _
 
+
 class FieldFile(File):
     def __init__(self, instance, field, name):
         super(FieldFile, self).__init__(None, name)
@@ -135,6 +136,7 @@ def __getstate__(self):
         # be restored later, by FileDescriptor below.
         return {'name': self.name, 'closed': False, '_committed': True, '_file': None}
 
+
 class FileDescriptor(object):
     """
     The descriptor for the file attribute on the model instance. Returns a
@@ -205,6 +207,7 @@ def __get__(self, instance=None, owner=None):
     def __set__(self, instance, value):
         instance.__dict__[self.field.name] = value
 
+
 class FileField(Field):
 
     # The class to wrap instance attributes in. Accessing the file object off
@@ -300,6 +303,7 @@ def formfield(self, **kwargs):
         defaults.update(kwargs)
         return super(FileField, self).formfield(**defaults)
 
+
 class ImageFileDescriptor(FileDescriptor):
     """
     Just like the FileDescriptor, but for ImageFields. The only difference is
@@ -321,14 +325,15 @@ def __set__(self, instance, value):
         if previous_file is not None:
             self.field.update_dimension_fields(instance, force=True)
 
-class ImageFieldFile(ImageFile, FieldFile):
 
+class ImageFieldFile(ImageFile, FieldFile):
     def delete(self, save=True):
         # Clear the image dimensions cache
         if hasattr(self, '_dimensions_cache'):
             del self._dimensions_cache
         super(ImageFieldFile, self).delete(save)
 
+
 class ImageField(FileField):
     attr_class = ImageFieldFile
     descriptor_class = ImageFileDescriptor
diff --git a/django/db/models/fields/proxy.py b/django/db/models/fields/proxy.py
index c0cc873f4cedb..29c782b59a325 100644
--- a/django/db/models/fields/proxy.py
+++ b/django/db/models/fields/proxy.py
@@ -5,6 +5,7 @@
 
 from django.db.models import fields
 
+
 class OrderWrt(fields.IntegerField):
     """
     A proxy for the _order database field that is used when
diff --git a/django/db/models/fields/related.py b/django/db/models/fields/related.py
index 1e7e73ddbe5f2..1034d8b2ac2cd 100644
--- a/django/db/models/fields/related.py
+++ b/django/db/models/fields/related.py
@@ -213,7 +213,7 @@ def __set__(self, instance, value):
 
         # If null=True, we can assign null here, but otherwise the value needs
         # to be an instance of the related class.
-        if value is None and self.related.field.null == False:
+        if value is None and self.related.field.null is False:
             raise ValueError('Cannot assign None: "%s.%s" does not allow null values.' %
                                 (instance._meta.object_name, self.related.get_accessor_name()))
         elif value is not None and not isinstance(value, self.related.model):
@@ -312,7 +312,7 @@ def __get__(self, instance, instance_type=None):
     def __set__(self, instance, value):
         # If null=True, we can assign null here, but otherwise the value needs
         # to be an instance of the related class.
-        if value is None and self.field.null == False:
+        if value is None and self.field.null is False:
             raise ValueError('Cannot assign None: "%s.%s" does not allow null values.' %
                                 (instance._meta.object_name, self.field.name))
         elif value is not None and not isinstance(value, self.field.rel.to):
@@ -397,7 +397,7 @@ class RelatedManager(superclass):
             def __init__(self, instance):
                 super(RelatedManager, self).__init__()
                 self.instance = instance
-                self.core_filters= {'%s__exact' % rel_field.name: instance}
+                self.core_filters = {'%s__exact' % rel_field.name: instance}
                 self.model = rel_model
 
             def get_queryset(self):
@@ -512,7 +512,6 @@ def __init__(self, model=None, query_field_name=None, instance=None, symmetrical
                                  "a many-to-many relationship can be used." %
                                  instance.__class__.__name__)
 
-
         def _get_fk_val(self, obj, field_name):
             """
             Returns the correct value for this relationship's foreign key. This
@@ -823,6 +822,7 @@ def __set__(self, instance, value):
         manager.clear()
         manager.add(*value)
 
+
 class ForeignObjectRel(object):
     def __init__(self, field, to, related_name=None, limit_choices_to=None,
                  parent_link=False, on_delete=None, related_query_name=None):
@@ -860,6 +860,7 @@ def set_field_name(self):
         # example custom multicolumn joins currently have no remote field).
         self.field_name = None
 
+
 class ManyToOneRel(ForeignObjectRel):
     def __init__(self, field, to, field_name, related_name=None, limit_choices_to=None,
                  parent_link=False, on_delete=None, related_query_name=None):
@@ -1125,7 +1126,7 @@ class ForeignKey(ForeignObject):
     def __init__(self, to, to_field=None, rel_class=ManyToOneRel,
                  db_constraint=True, **kwargs):
         try:
-            to_name = to._meta.object_name.lower()
+            to._meta.object_name.lower()
         except AttributeError:  # to._meta doesn't exist, so it must be RECURSIVE_RELATIONSHIP_CONSTANT
             assert isinstance(to, six.string_types), "%s(%r) is invalid. First parameter to ForeignKey must be either a model, a model name, or the string %r" % (self.__class__.__name__, to, RECURSIVE_RELATIONSHIP_CONSTANT)
         else:
@@ -1162,7 +1163,6 @@ def deconstruct(self):
         if self.rel.on_delete is not CASCADE:
             kwargs['on_delete'] = self.rel.on_delete
         # Rel needs more work.
-        rel = self.rel
         if self.rel.field_name:
             kwargs['to_field'] = self.rel.field_name
         if isinstance(self.rel.to, six.string_types):
@@ -1193,8 +1193,8 @@ def validate(self, value, model_instance):
 
         using = router.db_for_read(model_instance.__class__, instance=model_instance)
         qs = self.rel.to._default_manager.using(using).filter(
-                **{self.rel.field_name: value}
-             )
+          **{self.rel.field_name: value}
+         )
         qs = qs.complex_filter(self.rel.limit_choices_to)
         if not qs.exists():
             raise exceptions.ValidationError(
@@ -1222,7 +1222,7 @@ def get_default(self):
         return field_default
 
     def get_db_prep_save(self, value, connection):
-        if value == '' or value == None:
+        if value == '' or value is None:
             return None
         else:
             return self.related_field.get_db_prep_save(value,
@@ -1389,7 +1389,6 @@ def deconstruct(self):
         if "help_text" in kwargs:
             del kwargs['help_text']
         # Rel needs more work.
-        rel = self.rel
         if isinstance(self.rel.to, six.string_types):
             kwargs['to'] = self.rel.to
         else:
diff --git a/django/db/models/fields/subclassing.py b/django/db/models/fields/subclassing.py
index e6153aefe0491..591adb7121aa0 100644
--- a/django/db/models/fields/subclassing.py
+++ b/django/db/models/fields/subclassing.py
@@ -7,6 +7,7 @@
 seamlessly.
 """
 
+
 class SubfieldBase(type):
     """
     A metaclass for custom Field subclasses. This ensures the model's attribute
@@ -19,6 +20,7 @@ def __new__(cls, name, bases, attrs):
         )
         return new_class
 
+
 class Creator(object):
     """
     A placeholder class that provides a way to set the attribute on the model.
@@ -34,6 +36,7 @@ def __get__(self, obj, type=None):
     def __set__(self, obj, value):
         obj.__dict__[self.field.name] = self.field.to_python(value)
 
+
 def make_contrib(superclass, func=None):
     """
     Returns a suitable contribute_to_class() method for the Field subclass.
diff --git a/django/db/models/loading.py b/django/db/models/loading.py
index 40aa983c25232..fb61098bfa162 100644
--- a/django/db/models/loading.py
+++ b/django/db/models/loading.py
@@ -15,9 +15,11 @@
 __all__ = ('get_apps', 'get_app', 'get_models', 'get_model', 'register_models',
         'load_app', 'app_cache_ready')
 
+
 class UnavailableApp(Exception):
     pass
 
+
 class AppCache(object):
     """
     A cache that stores installed applications and their models. Used to
diff --git a/django/db/models/manager.py b/django/db/models/manager.py
index 6817c9c8ee0a1..065718249ecdb 100644
--- a/django/db/models/manager.py
+++ b/django/db/models/manager.py
@@ -6,6 +6,7 @@
 from django.utils import six
 from django.utils.deprecation import RenameMethodsBase
 
+
 def ensure_default_manager(sender, **kwargs):
     """
     Ensures that a Model subclass contains a default manager  and sets the
@@ -245,7 +246,7 @@ def __init__(self, manager):
         self.manager = manager
 
     def __get__(self, instance, type=None):
-        if instance != None:
+        if instance is not None:
             raise AttributeError("Manager isn't accessible via %s instances" % type.__name__)
         return self.manager
 
diff --git a/django/db/models/query.py b/django/db/models/query.py
index 2b8ce65e6fef3..8baef82bc7a47 100644
--- a/django/db/models/query.py
+++ b/django/db/models/query.py
@@ -351,7 +351,7 @@ def bulk_create(self, objs, batch_size=None):
                 if objs_with_pk:
                     self._batched_insert(objs_with_pk, fields, batch_size)
                 if objs_without_pk:
-                    fields= [f for f in fields if not isinstance(f, AutoField)]
+                    fields = [f for f in fields if not isinstance(f, AutoField)]
                     self._batched_insert(objs_without_pk, fields, batch_size)
 
         return objs
@@ -818,7 +818,7 @@ def _batched_insert(self, objs, fields, batch_size):
             return
         ops = connections[self.db].ops
         batch_size = (batch_size or max(ops.bulk_batch_size(fields, objs), 1))
-        for batch in [objs[i:i+batch_size]
+        for batch in [objs[i:i + batch_size]
                       for i in range(0, len(objs), batch_size)]:
             self.model._base_manager._insert(batch, fields=fields,
                                              using=self.db)
@@ -899,10 +899,12 @@ def _as_sql(self, connection):
     # empty" result.
     value_annotation = True
 
+
 class InstanceCheckMeta(type):
     def __instancecheck__(self, instance):
         return instance.query.is_empty()
 
+
 class EmptyQuerySet(six.with_metaclass(InstanceCheckMeta)):
     """
     Marker class usable for checking if a queryset is empty by .none():
@@ -912,6 +914,7 @@ class EmptyQuerySet(six.with_metaclass(InstanceCheckMeta)):
     def __init__(self, *args, **kwargs):
         raise TypeError("EmptyQuerySet can't be instantiated")
 
+
 class ValuesQuerySet(QuerySet):
     def __init__(self, *args, **kwargs):
         super(ValuesQuerySet, self).__init__(*args, **kwargs)
@@ -1240,7 +1243,7 @@ def get_klass_info(klass, max_depth=0, cur_depth=0, requested=None,
                                                          only_load.get(o.model), reverse=True):
                 next = requested[o.field.related_query_name()]
                 parent = klass if issubclass(o.model, klass) else None
-                klass_info = get_klass_info(o.model, max_depth=max_depth, cur_depth=cur_depth+1,
+                klass_info = get_klass_info(o.model, max_depth=max_depth, cur_depth=cur_depth + 1,
                                             requested=next, only_load=only_load, from_parent=parent)
                 reverse_related_fields.append((o.field, klass_info))
     if field_names:
@@ -1251,7 +1254,7 @@ def get_klass_info(klass, max_depth=0, cur_depth=0, requested=None,
     return klass, field_names, field_count, related_fields, reverse_related_fields, pk_idx
 
 
-def get_cached_row(row, index_start, using,  klass_info, offset=0,
+def get_cached_row(row, index_start, using, klass_info, offset=0,
                    parent_data=()):
     """
     Helper function that recursively returns an object with the specified
@@ -1276,11 +1279,10 @@ def get_cached_row(row, index_start, using,  klass_info, offset=0,
         return None
     klass, field_names, field_count, related_fields, reverse_related_fields, pk_idx = klass_info
 
-
-    fields = row[index_start : index_start + field_count]
+    fields = row[index_start:index_start + field_count]
     # If the pk column is None (or the Oracle equivalent ''), then the related
     # object must be non-existent - set the relation to None.
-    if fields[pk_idx] == None or fields[pk_idx] == '':
+    if fields[pk_idx] is None or fields[pk_idx] == '':
         obj = None
     elif field_names:
         fields = list(fields)
@@ -1510,8 +1512,6 @@ def prefetch_related_objects(result_cache, related_lookups):
     if len(result_cache) == 0:
         return # nothing to do
 
-    model = result_cache[0].__class__
-
     # We need to be able to dynamically add to the list of prefetch_related
     # lookups that we look up (see below).  So we need some book keeping to
     # ensure we don't do duplicate work.
@@ -1538,7 +1538,7 @@ def prefetch_related_objects(result_cache, related_lookups):
             if len(obj_list) == 0:
                 break
 
-            current_lookup = LOOKUP_SEP.join(attrs[0:level+1])
+            current_lookup = LOOKUP_SEP.join(attrs[:level + 1])
             if current_lookup in done_queries:
                 # Skip any prefetching, and any object preparation
                 obj_list = done_queries[current_lookup]
diff --git a/django/db/models/query_utils.py b/django/db/models/query_utils.py
index ee7a56a26c3ab..2a92978beb023 100644
--- a/django/db/models/query_utils.py
+++ b/django/db/models/query_utils.py
@@ -30,6 +30,7 @@ def __init__(self, sql, params):
     def as_sql(self, qn=None, connection=None):
         return self.data
 
+
 class Q(tree.Node):
     """
     Encapsulates filters as objects that can then be combined logically (using
@@ -74,6 +75,7 @@ def clone(self):
                 clone.children.append(child)
         return clone
 
+
 class DeferredAttribute(object):
     """
     A wrapper for a deferred-loading field. When the value is read from this
@@ -99,8 +101,7 @@ def __get__(self, instance, owner):
             try:
                 f = opts.get_field_by_name(self.field_name)[0]
             except FieldDoesNotExist:
-                f = [f for f in opts.fields
-                     if f.attname == self.field_name][0]
+                f = [f for f in opts.fields if f.attname == self.field_name][0]
             name = f.name
             # Let's see if the field is part of the parent chain. If so we
             # might be able to reuse the already loaded value. Refs #18343.
@@ -174,6 +175,7 @@ def select_related_descend(field, restricted, requested, load_fields, reverse=Fa
             return False
     return True
 
+
 # This function is needed because data descriptors must be defined on a class
 # object, not an instance, to have any effect.
 
diff --git a/django/db/models/related.py b/django/db/models/related.py
index 4b00dd343b288..ba2a90c5455e8 100644
--- a/django/db/models/related.py
+++ b/django/db/models/related.py
@@ -10,6 +10,7 @@
                       'from_opts to_opts target_fields join_field '
                       'm2m direct')
 
+
 class RelatedObject(object):
     def __init__(self, parent_model, model, field):
         self.parent_model = parent_model
diff --git a/django/db/models/sql/aggregates.py b/django/db/models/sql/aggregates.py
index 2bd2b2f76f4a6..9fc5fe8a5b44b 100644
--- a/django/db/models/sql/aggregates.py
+++ b/django/db/models/sql/aggregates.py
@@ -9,6 +9,7 @@
 ordinal_aggregate_field = IntegerField()
 computed_aggregate_field = FloatField()
 
+
 class Aggregate(object):
     """
     Default SQL Aggregate.
@@ -93,6 +94,7 @@ class Avg(Aggregate):
     is_computed = True
     sql_function = 'AVG'
 
+
 class Count(Aggregate):
     is_ordinal = True
     sql_function = 'COUNT'
@@ -101,12 +103,15 @@ class Count(Aggregate):
     def __init__(self, col, distinct=False, **extra):
         super(Count, self).__init__(col, distinct='DISTINCT ' if distinct else '', **extra)
 
+
 class Max(Aggregate):
     sql_function = 'MAX'
 
+
 class Min(Aggregate):
     sql_function = 'MIN'
 
+
 class StdDev(Aggregate):
     is_computed = True
 
@@ -114,9 +119,11 @@ def __init__(self, col, sample=False, **extra):
         super(StdDev, self).__init__(col, **extra)
         self.sql_function = 'STDDEV_SAMP' if sample else 'STDDEV_POP'
 
+
 class Sum(Aggregate):
     sql_function = 'SUM'
 
+
 class Variance(Aggregate):
     is_computed = True
 
diff --git a/django/db/models/sql/compiler.py b/django/db/models/sql/compiler.py
index f70750abed121..0b12bd1552d16 100644
--- a/django/db/models/sql/compiler.py
+++ b/django/db/models/sql/compiler.py
@@ -688,7 +688,7 @@ def fill_related_selections(self, opts=None, root_alias=None, cur_depth=1,
                 # the relation, which is always nullable.
                 new_nullable = True
                 table = model._meta.db_table
-                self.fill_related_selections(model._meta, table, cur_depth+1,
+                self.fill_related_selections(model._meta, table, cur_depth + 1,
                     next, restricted, new_nullable)
 
     def deferred_to_columns(self):
@@ -915,6 +915,7 @@ def as_sql(self):
             result.append('WHERE %s' % where)
         return ' '.join(result), tuple(params)
 
+
 class SQLUpdateCompiler(SQLCompiler):
     def as_sql(self):
         """
@@ -1029,6 +1030,7 @@ def pre_sql_setup(self):
         for alias in self.query.tables[1:]:
             self.query.alias_refcount[alias] = 0
 
+
 class SQLAggregateCompiler(SQLCompiler):
     def as_sql(self, qn=None):
         """
@@ -1050,6 +1052,7 @@ def as_sql(self, qn=None):
         params = params + self.query.sub_params
         return sql, params
 
+
 class SQLDateCompiler(SQLCompiler):
     def results_iter(self):
         """
@@ -1075,6 +1078,7 @@ def results_iter(self):
                     date = date.date()
                 yield date
 
+
 class SQLDateTimeCompiler(SQLCompiler):
     def results_iter(self):
         """
@@ -1107,6 +1111,7 @@ def results_iter(self):
                     datetime = timezone.make_aware(datetime, self.query.tzinfo)
                 yield datetime
 
+
 def order_modified_iter(cursor, trim, sentinel):
     """
     Yields blocks of rows from a cursor. We use this iterator in the special
diff --git a/django/db/models/sql/datastructures.py b/django/db/models/sql/datastructures.py
index daaabbe6da00c..76b3db5b35615 100644
--- a/django/db/models/sql/datastructures.py
+++ b/django/db/models/sql/datastructures.py
@@ -3,9 +3,11 @@
 the SQL domain.
 """
 
+
 class EmptyResultSet(Exception):
     pass
 
+
 class MultiJoin(Exception):
     """
     Used by join construction code to indicate the point at which a
@@ -17,12 +19,10 @@ def __init__(self, names_pos, path_with_names):
         # The path travelled, this includes the path to the multijoin.
         self.names_with_path = path_with_names
 
+
 class Empty(object):
     pass
 
-class RawValue(object):
-    def __init__(self, value):
-        self.value = value
 
 class Date(object):
     """
@@ -42,6 +42,7 @@ def as_sql(self, qn, connection):
             col = self.col
         return connection.ops.date_trunc_sql(self.lookup_type, col), []
 
+
 class DateTime(object):
     """
     Add a datetime selection column.
diff --git a/django/db/models/sql/expressions.py b/django/db/models/sql/expressions.py
index 62adf79d87771..f9a8929974c06 100644
--- a/django/db/models/sql/expressions.py
+++ b/django/db/models/sql/expressions.py
@@ -1,7 +1,9 @@
+import copy
+
 from django.core.exceptions import FieldError
 from django.db.models.constants import LOOKUP_SEP
 from django.db.models.fields import FieldDoesNotExist
-import copy
+
 
 class SQLEvaluator(object):
     def __init__(self, expression, query, allow_joins=True, reuse=None):
diff --git a/django/db/models/sql/query.py b/django/db/models/sql/query.py
index 75e8e7540d52b..110925114cf37 100644
--- a/django/db/models/sql/query.py
+++ b/django/db/models/sql/query.py
@@ -615,7 +615,6 @@ def deferred_to_data(self, target, callback):
             for model, values in six.iteritems(seen):
                 callback(target, model, values)
 
-
     def deferred_to_columns_cb(self, target, model, fields):
         """
         Callback used by deferred_to_columns(). The "target" parameter should
@@ -627,7 +626,6 @@ def deferred_to_columns_cb(self, target, model, fields):
         for field in fields:
             target[table].add(field.column)
 
-
     def table_alias(self, table_name, create=False):
         """
         Returns a table alias for the given table_name and whether this is a
@@ -955,7 +953,6 @@ def remove_inherited_models(self):
                 self.unref_alias(alias)
         self.included_inherited_models = {}
 
-
     def add_aggregate(self, aggregate, model, alias, is_summary):
         """
         Adds a single aggregate expression to the Query
@@ -1780,7 +1777,7 @@ def _aggregate_select(self):
             return self._aggregate_select_cache
         elif self.aggregate_select_mask is not None:
             self._aggregate_select_cache = SortedDict([
-                (k,v) for k,v in self.aggregates.items()
+                (k, v) for k, v in self.aggregates.items()
                 if k in self.aggregate_select_mask
             ])
             return self._aggregate_select_cache
@@ -1793,7 +1790,7 @@ def _extra_select(self):
             return self._extra_select_cache
         elif self.extra_select_mask is not None:
             self._extra_select_cache = SortedDict([
-                (k,v) for k,v in self.extra.items()
+                (k, v) for k, v in self.extra.items()
                 if k in self.extra_select_mask
             ])
             return self._extra_select_cache
@@ -1876,6 +1873,7 @@ def is_nullable(self, field):
         else:
             return field.null
 
+
 def get_order_dir(field, default='ASC'):
     """
     Returns the field name and direction for an order specification. For
@@ -1900,6 +1898,7 @@ def add_to_dict(data, key, value):
     else:
         data[key] = set([value])
 
+
 def is_reverse_o2o(field):
     """
     A little helper to check if the given field is reverse-o2o. The field is
@@ -1907,6 +1906,7 @@ def is_reverse_o2o(field):
     """
     return not hasattr(field, 'rel') and field.field.unique
 
+
 def alias_diff(refcounts_before, refcounts_after):
     """
     Given the before and after copies of refcounts works out which aliases
diff --git a/django/db/models/sql/subqueries.py b/django/db/models/sql/subqueries.py
index 20770162c9210..6aab02bd9ac96 100644
--- a/django/db/models/sql/subqueries.py
+++ b/django/db/models/sql/subqueries.py
@@ -7,7 +7,7 @@
 from django.db import connections
 from django.db.models.constants import LOOKUP_SEP
 from django.db.models.fields import DateField, DateTimeField, FieldDoesNotExist
-from django.db.models.sql.constants import *
+from django.db.models.sql.constants import GET_ITERATOR_CHUNK_SIZE, SelectInfo
 from django.db.models.sql.datastructures import Date, DateTime
 from django.db.models.sql.query import Query
 from django.db.models.sql.where import AND, Constraint
@@ -20,6 +20,7 @@
 __all__ = ['DeleteQuery', 'UpdateQuery', 'InsertQuery', 'DateQuery',
         'DateTimeQuery', 'AggregateQuery']
 
+
 class DeleteQuery(Query):
     """
     Delete queries are done through this class, since they are more constrained
@@ -77,7 +78,9 @@ def delete_qs(self, query, using):
                 return
             else:
                 innerq.clear_select_clause()
-                innerq.select = [SelectInfo((self.get_initial_alias(), pk.column), None)]
+                innerq.select = [
+                    SelectInfo((self.get_initial_alias(), pk.column), None)
+                ]
                 values = innerq
             where = self.where_class()
             where.add((Constraint(None, pk.column, pk), 'in', values), AND)
@@ -178,6 +181,7 @@ def get_related_updates(self):
             result.append(query)
         return result
 
+
 class InsertQuery(Query):
     compiler = 'SQLInsertCompiler'
 
@@ -215,6 +219,7 @@ def insert_values(self, fields, objs, raw=False):
         self.objs = objs
         self.raw = raw
 
+
 class DateQuery(Query):
     """
     A DateQuery is a normal query, except that it specifically selects a single
@@ -260,6 +265,7 @@ def _check_field(self, field):
     def _get_select(self, col, lookup_type):
         return Date(col, lookup_type)
 
+
 class DateTimeQuery(DateQuery):
     """
     A DateTimeQuery is like a DateQuery but for a datetime field. If time zone
@@ -280,6 +286,7 @@ def _get_select(self, col, lookup_type):
             tzname = timezone._get_timezone_name(self.tzinfo)
         return DateTime(col, lookup_type, tzname)
 
+
 class AggregateQuery(Query):
     """
     An AggregateQuery takes another query as a parameter to the FROM
diff --git a/django/db/models/sql/where.py b/django/db/models/sql/where.py
index 2a342d417acbe..024b995c99b87 100644
--- a/django/db/models/sql/where.py
+++ b/django/db/models/sql/where.py
@@ -16,10 +16,12 @@
 from django.utils import timezone
 from django.utils import tree
 
+
 # Connection types
 AND = 'AND'
 OR = 'OR'
 
+
 class EmptyShortCircuit(Exception):
     """
     Internal exception used to indicate that a "matches nothing" node should be
@@ -27,6 +29,7 @@ class EmptyShortCircuit(Exception):
     """
     pass
 
+
 class WhereNode(tree.Node):
     """
     Used to represent the SQL where-clause.
@@ -175,7 +178,7 @@ def make_atom(self, child, qn, connection):
         """
         lvalue, lookup_type, value_annotation, params_or_value = child
         field_internal_type = lvalue.field.get_internal_type() if lvalue.field else None
-        
+
         if isinstance(lvalue, Constraint):
             try:
                 lvalue, params = lvalue.process(lookup_type, params_or_value, connection)
@@ -304,14 +307,15 @@ def clone(self):
                 clone.children.append(child)
         return clone
 
-class EmptyWhere(WhereNode):
 
+class EmptyWhere(WhereNode):
     def add(self, data, connector):
         return
 
     def as_sql(self, qn=None, connection=None):
         raise EmptyResultSet
 
+
 class EverythingNode(object):
     """
     A node that matches everything.
@@ -385,6 +389,7 @@ def relabeled_clone(self, change_map):
             new.alias, new.col, new.field = change_map[self.alias], self.col, self.field
             return new
 
+
 class SubqueryConstraint(object):
     def __init__(self, alias, columns, targets, query_object):
         self.alias = alias
diff --git a/django/db/transaction.py b/django/db/transaction.py
index 96be981e7bf43..bb2dbb8e9e00c 100644
--- a/django/db/transaction.py
+++ b/django/db/transaction.py
@@ -27,6 +27,7 @@ class TransactionManagementError(Exception):
     """
     pass
 
+
 ################
 # Private APIs #
 ################
@@ -40,6 +41,7 @@ def get_connection(using=None):
         using = DEFAULT_DB_ALIAS
     return connections[using]
 
+
 ###########################
 # Deprecated private APIs #
 ###########################
@@ -56,6 +58,7 @@ def abort(using=None):
     """
     get_connection(using).abort()
 
+
 def enter_transaction_management(managed=True, using=None, forced=False):
     """
     Enters transaction management for a running thread. It must be balanced with
@@ -68,6 +71,7 @@ def enter_transaction_management(managed=True, using=None, forced=False):
     """
     get_connection(using).enter_transaction_management(managed, forced)
 
+
 def leave_transaction_management(using=None):
     """
     Leaves transaction management for a running thread. A dirty flag is carried
@@ -76,6 +80,7 @@ def leave_transaction_management(using=None):
     """
     get_connection(using).leave_transaction_management()
 
+
 def is_dirty(using=None):
     """
     Returns True if the current transaction requires a commit for changes to
@@ -83,6 +88,7 @@ def is_dirty(using=None):
     """
     return get_connection(using).is_dirty()
 
+
 def set_dirty(using=None):
     """
     Sets a dirty flag for the current thread and code streak. This can be used
@@ -91,6 +97,7 @@ def set_dirty(using=None):
     """
     get_connection(using).set_dirty()
 
+
 def set_clean(using=None):
     """
     Resets a dirty flag for the current thread and code streak. This can be used
@@ -99,22 +106,27 @@ def set_clean(using=None):
     """
     get_connection(using).set_clean()
 
+
 def is_managed(using=None):
     warnings.warn("'is_managed' is deprecated.",
         DeprecationWarning, stacklevel=2)
 
+
 def managed(flag=True, using=None):
     warnings.warn("'managed' no longer serves a purpose.",
         DeprecationWarning, stacklevel=2)
 
+
 def commit_unless_managed(using=None):
     warnings.warn("'commit_unless_managed' is now a no-op.",
         DeprecationWarning, stacklevel=2)
 
+
 def rollback_unless_managed(using=None):
     warnings.warn("'rollback_unless_managed' is now a no-op.",
         DeprecationWarning, stacklevel=2)
 
+
 ###############
 # Public APIs #
 ###############
@@ -125,24 +137,28 @@ def get_autocommit(using=None):
     """
     return get_connection(using).get_autocommit()
 
+
 def set_autocommit(autocommit, using=None):
     """
     Set the autocommit status of the connection.
     """
     return get_connection(using).set_autocommit(autocommit)
 
+
 def commit(using=None):
     """
     Commits a transaction and resets the dirty flag.
     """
     get_connection(using).commit()
 
+
 def rollback(using=None):
     """
     Rolls back a transaction and resets the dirty flag.
     """
     get_connection(using).rollback()
 
+
 def savepoint(using=None):
     """
     Creates a savepoint (if supported and required by the backend) inside the
@@ -151,6 +167,7 @@ def savepoint(using=None):
     """
     return get_connection(using).savepoint()
 
+
 def savepoint_rollback(sid, using=None):
     """
     Rolls back the most recent savepoint (if one exists). Does nothing if
@@ -158,6 +175,7 @@ def savepoint_rollback(sid, using=None):
     """
     get_connection(using).savepoint_rollback(sid)
 
+
 def savepoint_commit(sid, using=None):
     """
     Commits the most recent savepoint (if one exists). Does nothing if
@@ -165,18 +183,21 @@ def savepoint_commit(sid, using=None):
     """
     get_connection(using).savepoint_commit(sid)
 
+
 def clean_savepoints(using=None):
     """
     Resets the counter used to generate unique savepoint ids in this thread.
     """
     get_connection(using).clean_savepoints()
 
+
 def get_rollback(using=None):
     """
     Gets the "needs rollback" flag -- for *advanced use* only.
     """
     return get_connection(using).get_rollback()
 
+
 def set_rollback(rollback, using=None):
     """
     Sets or unsets the "needs rollback" flag -- for *advanced use* only.
@@ -191,6 +212,7 @@ def set_rollback(rollback, using=None):
     """
     return get_connection(using).set_rollback(rollback)
 
+
 #################################
 # Decorators / context managers #
 #################################
@@ -398,6 +420,7 @@ def inner(*args, **kwargs):
                 return func(*args, **kwargs)
         return inner
 
+
 def _transaction_func(entering, exiting, using):
     """
     Takes 3 things, an entering function (what to do to start this block of
@@ -436,6 +459,7 @@ def exiting(exc_value, using):
 
     return _transaction_func(entering, exiting, using)
 
+
 def commit_on_success(using=None):
     """
     This decorator activates commit on response. This way, if the view function
@@ -466,6 +490,7 @@ def exiting(exc_value, using):
 
     return _transaction_func(entering, exiting, using)
 
+
 def commit_manually(using=None):
     """
     Decorator that activates manual transaction control. It just disables
@@ -484,6 +509,7 @@ def exiting(exc_value, using):
 
     return _transaction_func(entering, exiting, using)
 
+
 def commit_on_success_unless_managed(using=None, savepoint=False):
     """
     Transitory API to preserve backwards-compatibility while refactoring.