diff --git a/graphene_django/rest_framework/mutation.py b/graphene_django/rest_framework/mutation.py
index 061c61f..d9ec2c8 100644
--- a/graphene_django/rest_framework/mutation.py
+++ b/graphene_django/rest_framework/mutation.py
@@ -23,13 +23,13 @@ class SerializerMutationOptions(MutationOptions):
 
 
 def fields_for_serializer(
-        serializer,
-        only_fields,
-        exclude_fields,
-        is_input=False,
-        convert_choices_to_enum=True,
-        lookup_field=None,
-        optional_fields=(),
+    serializer,
+    only_fields,
+    exclude_fields,
+    is_input=False,
+    convert_choices_to_enum=True,
+    lookup_field=None,
+    optional_fields=(),
 ):
     fields = OrderedDict()
     for name, field in serializer.fields.items():
@@ -50,11 +50,13 @@ def fields_for_serializer(
 
         if is_not_in_only or is_excluded:
             continue
-        is_optional = name in optional_fields or '__all__' in optional_fields
+        is_optional = name in optional_fields or "__all__" in optional_fields
 
         fields[name] = convert_serializer_field(
-            field, is_input=is_input, convert_choices_to_enum=convert_choices_to_enum,
-            force_optional=is_optional
+            field,
+            is_input=is_input,
+            convert_choices_to_enum=convert_choices_to_enum,
+            force_optional=is_optional,
         )
     return fields
 
@@ -69,17 +71,16 @@ class SerializerMutation(ClientIDMutation):
 
     @classmethod
     def __init_subclass_with_meta__(
-            cls,
-            lookup_field=None,
-            serializer_class=None,
-            model_class=None,
-            model_operations=("create", "update"),
-            only_fields=(),
-            exclude_fields=(),
-            convert_choices_to_enum=True,
-            _meta=None,
-            optional_fields=()
-            **options
+        cls,
+        lookup_field=None,
+        serializer_class=None,
+        model_class=None,
+        model_operations=("create", "update"),
+        only_fields=(),
+        exclude_fields=(),
+        convert_choices_to_enum=True,
+        _meta=None,
+        optional_fields=() ** options,
     ):
         if not serializer_class:
             raise Exception("serializer_class is required for the SerializerMutation")
@@ -103,7 +104,7 @@ class SerializerMutation(ClientIDMutation):
             is_input=True,
             convert_choices_to_enum=convert_choices_to_enum,
             lookup_field=lookup_field,
-            optional_fields=optional_fields
+            optional_fields=optional_fields,
         )
         output_fields = fields_for_serializer(
             serializer,
diff --git a/graphene_django/rest_framework/serializer_converter.py b/graphene_django/rest_framework/serializer_converter.py
index deab7d2..51695c5 100644
--- a/graphene_django/rest_framework/serializer_converter.py
+++ b/graphene_django/rest_framework/serializer_converter.py
@@ -18,8 +18,9 @@ def get_graphene_type_from_serializer_field(field):
     )
 
 
-def convert_serializer_field(field, is_input=True, convert_choices_to_enum=True,
-                             force_optional=False):
+def convert_serializer_field(
+    field, is_input=True, convert_choices_to_enum=True, force_optional=False
+):
     """
     Converts a django rest frameworks field to a graphql field
     and marks the field as required if we are creating an input type
@@ -32,7 +33,10 @@ def convert_serializer_field(field, is_input=True, convert_choices_to_enum=True,
         graphql_type = get_graphene_type_from_serializer_field(field)
 
     args = []
-    kwargs = {"description": field.help_text, "required": is_input and field.required and not force_optional}
+    kwargs = {
+        "description": field.help_text,
+        "required": is_input and field.required and not force_optional,
+    }
 
     # if it is a tuple or a list it means that we are returning
     # the graphql type and the child type
diff --git a/graphene_django/rest_framework/tests/test_mutation.py b/graphene_django/rest_framework/tests/test_mutation.py
index 9159d32..bfb2f17 100644
--- a/graphene_django/rest_framework/tests/test_mutation.py
+++ b/graphene_django/rest_framework/tests/test_mutation.py
@@ -104,6 +104,7 @@ def test_exclude_fields():
     assert "cool_name" in MyMutation.Input._meta.fields
     assert "created" not in MyMutation.Input._meta.fields
 
+
 def test_model_serializer_optional_fields():
     class MyMutation(SerializerMutation):
         class Meta: