diff --git a/manual/plugin_examples/editor_demo/__init__.py b/manual/plugin_examples/editor_demo/__init__.py
index a6c63eadf0..ad00975893 100644
--- a/manual/plugin_examples/editor_demo/__init__.py
+++ b/manual/plugin_examples/editor_demo/__init__.py
@@ -1,5 +1,4 @@
 #!/usr/bin/env python
-# vim:fileencoding=utf-8
 
 
 __license__ = 'GPL v3'
diff --git a/manual/plugin_examples/editor_demo/main.py b/manual/plugin_examples/editor_demo/main.py
index 3da2fb442d..657aad7727 100644
--- a/manual/plugin_examples/editor_demo/main.py
+++ b/manual/plugin_examples/editor_demo/main.py
@@ -1,5 +1,4 @@
 #!/usr/bin/env python
-# vim:fileencoding=utf-8
 
 
 __license__ = 'GPL v3'
diff --git a/manual/plugin_examples/interface_demo/main.py b/manual/plugin_examples/interface_demo/main.py
index 2e6fd25df7..5f58b06ec4 100644
--- a/manual/plugin_examples/interface_demo/main.py
+++ b/manual/plugin_examples/interface_demo/main.py
@@ -145,7 +145,7 @@ class DemoDialog(QDialog):
                 db.add_format(book_id, fmt, ffile, run_hooks=False)
 
         info_dialog(self, 'Updated files',
-                'Updated the metadata in the files of %d book(s)'%len(ids),
+                f'Updated the metadata in the files of {len(ids)} book(s)',
                 show=True)
 
     def config(self):
diff --git a/pyproject.toml b/pyproject.toml
index 0aee19121d..ed989d9191 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -47,12 +47,10 @@ unfixable = ['PIE794', 'ISC001']
 
 [tool.ruff.lint.per-file-ignores]
 "recipes/*" = ['UP']
-"manual/plugin_examples/*" = ['UP']
 "setup/changelog.py" = ['ISC001']
 "src/calibre/*" = ['UP031']
 "src/calibre/ebooks/unihandecode/*codepoints.py" = ['E501']
 "src/calibre/ebooks/metadata/sources/*" = ['UP']
-"src/calibre/ebooks/metadata/sources/base.py" = ['RET501']
 "src/calibre/gui2/store/stores/*" = ['UP']
 "src/qt/*.py" = ['I', 'E302']
 "src/qt/*.pyi" = ['I']
diff --git a/src/calibre/ebooks/metadata/sources/base.py b/src/calibre/ebooks/metadata/sources/base.py
index cc9b16f789..ef2de2f3b2 100644
--- a/src/calibre/ebooks/metadata/sources/base.py
+++ b/src/calibre/ebooks/metadata/sources/base.py
@@ -487,7 +487,7 @@ class Source(Plugin):
         consistent, so only implement it if it is possible to construct the URL
         from a known scheme given identifiers.
         '''
-        return None
+        return
 
     def get_book_url_name(self, idtype, idval, url):
         '''
@@ -513,7 +513,7 @@ class Source(Plugin):
         Note that this method must only return validated URLs, i.e. not URLS
         that could result in a generic cover image or a not found error.
         '''
-        return None
+        return
 
     def id_from_url(self, url):
         '''
@@ -522,7 +522,7 @@ class Source(Plugin):
         If the URL does not match the pattern for the metadata source,
         return None.
         '''
-        return None
+        return
 
     def identify_results_keygen(self, title=None, authors=None,
             identifiers={}):
@@ -581,7 +581,7 @@ class Source(Plugin):
                  of the error suitable for showing to the user
 
         '''
-        return None
+        return
 
     def download_cover(self, log, result_queue, abort,
             title=None, authors=None, identifiers={}, timeout=30, get_best_cover=False):