diff --git a/docs/tutorial/6-viewsets-and-routers.md b/docs/tutorial/6-viewsets-and-routers.md
index e12becbd0..b7a7696a7 100644
--- a/docs/tutorial/6-viewsets-and-routers.md
+++ b/docs/tutorial/6-viewsets-and-routers.md
@@ -112,8 +112,8 @@ Here's our re-wired `snippets/urls.py` file.
 
     # Create a router and register our viewsets with it.
     router = DefaultRouter()
-    router.register(r'snippets', views.SnippetViewSet,basename="snippet")
-    router.register(r'users', views.UserViewSet,basename="user")
+    router.register(r'snippets', views.SnippetViewSet, basename='snippet')
+    router.register(r'users', views.UserViewSet, basename='user')
 
     # The API URLs are now determined automatically by the router.
     urlpatterns = [
diff --git a/requirements/requirements-testing.txt b/requirements/requirements-testing.txt
index 313fdedc9..f6823e2e2 100644
--- a/requirements/requirements-testing.txt
+++ b/requirements/requirements-testing.txt
@@ -2,3 +2,4 @@
 pytest>=6.1,<7.0
 pytest-cov>=2.10.1,<3.0
 pytest-django>=4.1.0,<5.0
+importlib-metadata<5.0
diff --git a/rest_framework/fields.py b/rest_framework/fields.py
index 6374c1ea9..a6924bf23 100644
--- a/rest_framework/fields.py
+++ b/rest_framework/fields.py
@@ -1814,7 +1814,7 @@ class SerializerMethodField(Field):
 
     For example:
 
-    class ExampleSerializer(self):
+    class ExampleSerializer(Serializer):
         extra_info = SerializerMethodField()
 
         def get_extra_info(self, obj):