diff --git a/rest_framework/renderers.py b/rest_framework/renderers.py
index ddfc027e0..e8740d57b 100644
--- a/rest_framework/renderers.py
+++ b/rest_framework/renderers.py
@@ -856,8 +856,8 @@ class DocumentationRenderer(BaseRenderer):
         return {
             'document': data,
             'langs': self.languages,
-            'lang_htmls': ["rest_framework/docs/langs/%s.html" % language for language in self.languages],
-            'lang_intro_htmls': ["rest_framework/docs/langs/%s-intro.html" % language for language in self.languages],
+            'lang_htmls': [f"rest_framework/docs/langs/{language}.html" for language in self.languages],
+            'lang_intro_htmls': [f"rest_framework/docs/langs/{language}-intro.html" for language in self.languages],
             'code_style': pygments_css(self.code_style),
             'request': request
         }
diff --git a/rest_framework/serializers.py b/rest_framework/serializers.py
index 10cd79227..48747e687 100644
--- a/rest_framework/serializers.py
+++ b/rest_framework/serializers.py
@@ -1375,7 +1375,7 @@ class ModelSerializer(Serializer):
             if not isinstance(read_only_fields, (list, tuple)):
                 raise TypeError(
                     'The `read_only_fields` option must be a list or tuple. '
-                    'Got %s.' % type(read_only_fields).__name__
+                    f'Got {type(read_only_fields).__name__}.'
                 )
             for field_name in read_only_fields:
                 kwargs = extra_kwargs.get(field_name, {})
diff --git a/rest_framework/templatetags/rest_framework.py b/rest_framework/templatetags/rest_framework.py
index 58f0d45c8..0dbaa196e 100644
--- a/rest_framework/templatetags/rest_framework.py
+++ b/rest_framework/templatetags/rest_framework.py
@@ -194,7 +194,7 @@ def add_class(value, css_class):
             return mark_safe(class_re.sub(match.group(1) + " " + css_class,
                                           html))
     else:
-        return mark_safe(html.replace('>', ' class="%s">' % css_class, 1))
+        return mark_safe(html.replace('>', f' class="{css_class}">', 1))
     return value
 
 
@@ -202,7 +202,7 @@ def add_class(value, css_class):
 def format_value(value):
     if getattr(value, 'is_hyperlink', False):
         name = str(value.obj)
-        return mark_safe('<a href=%s>%s</a>' % (value, escape(name)))
+        return mark_safe(f'<a href={value}>{escape(name)}</a>')
     if value is None or isinstance(value, bool):
         return mark_safe('<code>%s</code>' % {True: 'true', False: 'false', None: 'null'}[value])
     elif isinstance(value, list):
@@ -218,8 +218,8 @@ def format_value(value):
         return template.render(context)
     elif isinstance(value, str):
         if (
-            (value.startswith('http:') or value.startswith('https:')) and not
-            re.search(r'\s', value)
+                (value.startswith('http:') or value.startswith('https:')) and not
+        re.search(r'\s', value)
         ):
             return mark_safe('<a href="{value}">{value}</a>'.format(value=escape(value)))
         elif '@' in value and not re.search(r'\s', value):