diff --git a/graphene/relay/connection.py b/graphene/relay/connection.py
index 0711ad87..9a06e1eb 100644
--- a/graphene/relay/connection.py
+++ b/graphene/relay/connection.py
@@ -6,7 +6,7 @@ import six
 
 from graphql_relay import connection_from_list
 
-from ..types import Boolean, Int, List, String, AbstractType
+from ..types import AbstractType, Boolean, Int, List, String
 from ..types.field import Field
 from ..types.objecttype import ObjectType, ObjectTypeMeta
 from ..types.options import Options
diff --git a/graphene/relay/mutation.py b/graphene/relay/mutation.py
index 6acc0674..50851781 100644
--- a/graphene/relay/mutation.py
+++ b/graphene/relay/mutation.py
@@ -2,9 +2,10 @@ import re
 from functools import partial
 
 import six
+
 from promise import Promise
 
-from ..types import Argument, Field, InputObjectType, String, AbstractType
+from ..types import AbstractType, Argument, Field, InputObjectType, String
 from ..types.objecttype import ObjectType, ObjectTypeMeta
 from ..utils.is_base_type import is_base_type
 from ..utils.props import props
diff --git a/graphene/relay/node.py b/graphene/relay/node.py
index f73f6a53..85d69276 100644
--- a/graphene/relay/node.py
+++ b/graphene/relay/node.py
@@ -57,6 +57,7 @@ class NodeMeta(InterfaceMeta):
 
 
 class NodeField(Field):
+
     def __init__(self, node, type=False, deprecation_reason=None,
                  name=None, **kwargs):
         assert issubclass(node, Node), 'NodeField can only operate in Nodes'
diff --git a/graphene/relay/tests/test_connection.py b/graphene/relay/tests/test_connection.py
index 2f1441ac..d2279254 100644
--- a/graphene/relay/tests/test_connection.py
+++ b/graphene/relay/tests/test_connection.py
@@ -1,5 +1,5 @@
 
-from ...types import Field, List, NonNull, ObjectType, String, AbstractType
+from ...types import AbstractType, Field, List, NonNull, ObjectType, String
 from ..connection import Connection, PageInfo
 from ..node import Node
 
@@ -41,6 +41,7 @@ def test_connection_inherit_abstracttype():
         extra = String()
 
     class MyObjectConnection(BaseConnection, Connection):
+
         class Meta:
             node = MyObject
 
@@ -51,6 +52,7 @@ def test_connection_inherit_abstracttype():
 
 def test_edge():
     class MyObjectConnection(Connection):
+
         class Meta:
             node = MyObject
 
@@ -74,6 +76,7 @@ def test_edge_with_bases():
         extra = String()
 
     class MyObjectConnection(Connection):
+
         class Meta:
             node = MyObject
 
diff --git a/graphene/relay/tests/test_connection_query.py b/graphene/relay/tests/test_connection_query.py
index b2c10c31..7a197f27 100644
--- a/graphene/relay/tests/test_connection_query.py
+++ b/graphene/relay/tests/test_connection_query.py
@@ -1,14 +1,16 @@
 from collections import OrderedDict
 
+from graphql_relay.utils import base64
+
+from ...types import ObjectType, Schema, String
 from ..connection import ConnectionField
 from ..node import Node
-from graphql_relay.utils import base64
-from ...types import ObjectType, String, Schema
 
 letter_chars = ['A', 'B', 'C', 'D', 'E']
 
 
 class Letter(ObjectType):
+
     class Meta:
         interfaces = (Node, )
 
@@ -163,7 +165,13 @@ def test_returns_all_elements_if_cursors_are_invalid():
 
 
 def test_returns_all_elements_if_cursors_are_on_the_outside():
-    check('before: "{}" after: "{}"'.format(base64('arrayconnection:%s' % 6), base64('arrayconnection:%s' % -1)), 'ABCDE')
+    check(
+        'before: "{}" after: "{}"'.format(
+            base64(
+                'arrayconnection:%s' % 6),
+            base64(
+                'arrayconnection:%s' % -1)),
+        'ABCDE')
 
 
 def test_returns_no_elements_if_cursors_cross():
diff --git a/graphene/relay/tests/test_mutation.py b/graphene/relay/tests/test_mutation.py
index f8502df0..8f414c33 100644
--- a/graphene/relay/tests/test_mutation.py
+++ b/graphene/relay/tests/test_mutation.py
@@ -1,10 +1,8 @@
-from collections import OrderedDict
 import pytest
 
-from ...types import (Argument, Field, InputField, InputObjectType, ObjectType,
-                      Schema, AbstractType, NonNull)
+from ...types import (AbstractType, Argument, Field, InputField,
+                      InputObjectType, NonNull, ObjectType, Schema)
 from ...types.scalars import String
-from ..connection import Connection
 from ..mutation import ClientIDMutation
 from ..node import Node
 
diff --git a/graphene/relay/tests/test_node.py b/graphene/relay/tests/test_node.py
index ef35f409..12c7c2c2 100644
--- a/graphene/relay/tests/test_node.py
+++ b/graphene/relay/tests/test_node.py
@@ -1,9 +1,8 @@
 from collections import OrderedDict
-import pytest
 
 from graphql_relay import to_global_id
 
-from ...types import ObjectType, Schema, String, AbstractType
+from ...types import AbstractType, ObjectType, Schema, String
 from ..connection import Connection
 from ..node import Node
 
@@ -72,10 +71,11 @@ def test_node_query():
 
 def test_subclassed_node_query():
     executed = schema.execute(
-        '{ node(id:"%s") { ... on MyOtherNode { shared, extraField, somethingElse } } }' % to_global_id("MyOtherNode", 1)
-    )
+        '{ node(id:"%s") { ... on MyOtherNode { shared, extraField, somethingElse } } }' %
+        to_global_id("MyOtherNode", 1))
     assert not executed.errors
-    assert executed.data == OrderedDict({'node': OrderedDict([('shared', '1'), ('extraField', 'extra field info.'), ('somethingElse', '----')])})
+    assert executed.data == OrderedDict({'node': OrderedDict(
+        [('shared', '1'), ('extraField', 'extra field info.'), ('somethingElse', '----')])})
 
 
 def test_node_query_incorrect_id():
diff --git a/graphene/types/__init__.py b/graphene/types/__init__.py
index 179c6f6d..fcb3fbfd 100644
--- a/graphene/types/__init__.py
+++ b/graphene/types/__init__.py
@@ -36,4 +36,5 @@ __all__ = [
     'NonNull',
     'Argument',
     'Dynamic',
+    'Union',
 ]
diff --git a/graphene/types/abstracttype.py b/graphene/types/abstracttype.py
index 6a7e7152..a5bbb73e 100644
--- a/graphene/types/abstracttype.py
+++ b/graphene/types/abstracttype.py
@@ -2,8 +2,7 @@ import six
 
 from ..utils.is_base_type import is_base_type
 from .options import Options
-from .utils import (yank_fields_from_attrs, get_base_fields,
-                    merge)
+from .utils import get_base_fields, merge, yank_fields_from_attrs
 
 
 class AbstractTypeMeta(type):
diff --git a/graphene/types/inputobjecttype.py b/graphene/types/inputobjecttype.py
index 67982c8b..2dc91cd5 100644
--- a/graphene/types/inputobjecttype.py
+++ b/graphene/types/inputobjecttype.py
@@ -2,10 +2,10 @@ import six
 
 from ..utils.is_base_type import is_base_type
 from .abstracttype import AbstractTypeMeta
+from .inputfield import InputField
 from .options import Options
 from .unmountedtype import UnmountedType
-from .utils import yank_fields_from_attrs, get_base_fields, merge
-from .inputfield import InputField
+from .utils import get_base_fields, merge, yank_fields_from_attrs
 
 
 class InputObjectTypeMeta(AbstractTypeMeta):
diff --git a/graphene/types/interface.py b/graphene/types/interface.py
index a67ce914..f5a2d61a 100644
--- a/graphene/types/interface.py
+++ b/graphene/types/interface.py
@@ -2,9 +2,9 @@ import six
 
 from ..utils.is_base_type import is_base_type
 from .abstracttype import AbstractTypeMeta
-from .options import Options
-from .utils import yank_fields_from_attrs, get_base_fields, merge
 from .field import Field
+from .options import Options
+from .utils import get_base_fields, merge, yank_fields_from_attrs
 
 
 class InterfaceMeta(AbstractTypeMeta):
diff --git a/graphene/types/objecttype.py b/graphene/types/objecttype.py
index 91b74c0f..ca3f6b0c 100644
--- a/graphene/types/objecttype.py
+++ b/graphene/types/objecttype.py
@@ -4,10 +4,10 @@ import six
 
 from ..utils.is_base_type import is_base_type
 from .abstracttype import AbstractTypeMeta
+from .field import Field
 from .interface import Interface
 from .options import Options
-from .utils import yank_fields_from_attrs, get_base_fields, merge
-from .field import Field
+from .utils import get_base_fields, merge, yank_fields_from_attrs
 
 
 class ObjectTypeMeta(AbstractTypeMeta):
diff --git a/graphene/types/structures.py b/graphene/types/structures.py
index 63fc2c2a..6cf0e4aa 100644
--- a/graphene/types/structures.py
+++ b/graphene/types/structures.py
@@ -40,6 +40,7 @@ class NonNull(Structure):
 
     Note: the enforcement of non-nullability occurs within the executor.
     '''
+
     def __init__(self, *args, **kwargs):
         super(NonNull, self).__init__(*args, **kwargs)
         assert not isinstance(self.of_type, NonNull), (
diff --git a/graphene/types/tests/test_query.py b/graphene/types/tests/test_query.py
index dd6de01c..b31aa046 100644
--- a/graphene/types/tests/test_query.py
+++ b/graphene/types/tests/test_query.py
@@ -1,12 +1,12 @@
 import json
 from functools import partial
 
-from graphql import execute, Source, parse
+from graphql import Source, execute, parse
 
-from ..objecttype import ObjectType
 from ..inputfield import InputField
 from ..inputobjecttype import InputObjectType
-from ..scalars import String, Int
+from ..objecttype import ObjectType
+from ..scalars import Int, String
 from ..schema import Schema
 from ..structures import List
 
diff --git a/graphene/types/tests/test_typemap.py b/graphene/types/tests/test_typemap.py
index 4d427a0a..974b633e 100644
--- a/graphene/types/tests/test_typemap.py
+++ b/graphene/types/tests/test_typemap.py
@@ -1,16 +1,16 @@
 
 from graphql.type import (GraphQLArgument, GraphQLEnumType, GraphQLEnumValue,
-                          GraphQLField, GraphQLObjectType, GraphQLString,
-                          GraphQLInterfaceType, GraphQLInputObjectField,
-                          GraphQLInputObjectType)
+                          GraphQLField, GraphQLInputObjectField,
+                          GraphQLInputObjectType, GraphQLInterfaceType,
+                          GraphQLObjectType, GraphQLString)
 
 from ..dynamic import Dynamic
 from ..enum import Enum
 from ..field import Field
 from ..inputfield import InputField
-from ..objecttype import ObjectType
 from ..inputobjecttype import InputObjectType
 from ..interface import Interface
+from ..objecttype import ObjectType
 from ..scalars import String
 from ..typemap import TypeMap
 
@@ -112,7 +112,7 @@ def test_interface():
     foo_field = fields['foo']
     assert isinstance(foo_field, GraphQLField)
     assert foo_field.description == 'Field description'
-    assert not foo_field.resolver # Resolver not attached in interfaces
+    assert not foo_field.resolver  # Resolver not attached in interfaces
     assert foo_field.args == {
         'bar': GraphQLArgument(GraphQLString, description='Argument description', default_value='x', out_name='bar')
     }