diff --git a/nikola/nikola.py b/nikola/nikola.py
index 4accadcc4..dd39e82d9 100644
--- a/nikola/nikola.py
+++ b/nikola/nikola.py
@@ -55,20 +55,7 @@
 from .post import Post  # NOQA
 from .plugin_manager import PluginCandidate, PluginInfo, PluginManager
 from .plugin_categories import (
-    Command,
-    LateTask,
-    PageCompiler,
-    CompilerExtension,
-    MarkdownExtension,
-    RestExtension,
-    MetadataExtractor,
-    ShortcodePlugin,
-    Task,
-    TaskMultiplier,
     TemplateSystem,
-    SignalHandler,
-    ConfigPlugin,
-    CommentSystem,
     PostScanner,
     Taxonomy,
 )
@@ -1050,7 +1037,6 @@ def init_plugins(self, commands_only=False, load_all=False):
         ] + [path for path in extra_plugins_dirs if path]
         self._plugin_places = [pathlib.Path(p) for p in self._plugin_places]
 
-
         self.plugin_manager = PluginManager(plugin_places=self._plugin_places)
 
         compilers = defaultdict(set)
diff --git a/nikola/plugin_categories.py b/nikola/plugin_categories.py
index 2abef7ed1..980f9106a 100644
--- a/nikola/plugin_categories.py
+++ b/nikola/plugin_categories.py
@@ -885,6 +885,7 @@ def get_other_language_variants(self, classification: str, lang: str, classifica
         """
         return []
 
+
 CATEGORIES = {
     "Command": Command,
     "Task": Task,
diff --git a/nikola/plugin_manager.py b/nikola/plugin_manager.py
index a9a95bf6f..f1ec91f23 100644
--- a/nikola/plugin_manager.py
+++ b/nikola/plugin_manager.py
@@ -142,6 +142,7 @@ def locate_plugins(self, force=False) -> List[PluginCandidate]:
         return self.candidates
 
     def load_plugins(self, candidates: List[PluginCandidate]) -> None:
+        """Load selected candidate plugins."""
         plugins_root = Path(__file__).parent.parent
 
         for candidate in candidates:
@@ -178,7 +179,7 @@ def load_plugins(self, candidates: List[PluginCandidate]) -> None:
                     module_object = importlib.util.module_from_spec(spec)
                     sys.modules[full_module_name] = module_object
                     spec.loader.exec_module(module_object)
-                except Exception as exc:
+                except Exception:
                     self.logger.exception(f"{plugin_id} threw an exception while loading")
                     continue
 
@@ -195,7 +196,7 @@ def load_plugins(self, candidates: List[PluginCandidate]) -> None:
                 continue
             try:
                 plugin_object = plugin_classes[0]()
-            except Exception as exc:
+            except Exception:
                 self.logger.exception(f"{plugin_id} threw an exception while creating an instance")
                 continue
             self.logger.debug(f"Loaded {plugin_id}")
@@ -217,16 +218,20 @@ def load_plugins(self, candidates: List[PluginCandidate]) -> None:
             self._plugins_by_category[plugin_info.category].append(plugin_info)
 
     def get_plugins_of_category(self, category: str) -> List[PluginInfo]:
+        """Get loaded plugins of a given category."""
         return self._plugins_by_category.get(category, [])
 
-    def get_plugin_by_name(self, name: str, category: str | None = None) -> PluginInfo | None:
+    def get_plugin_by_name(self, name: str, category: Optional[str] = None) -> Optional[PluginInfo]:
+        """Get a loaded plugin by name and optionally by category. Returns None if no such plugin is loaded."""
         for p in self.plugins:
             if p.name == name and (category is None or p.category == category):
                 return p
 
     # Aliases for Yapsy compatibility
     def getPluginsOfCategory(self, category: str) -> List[PluginInfo]:
+        """Get loaded plugins of a given category."""
         return self._plugins_by_category.get(category, [])
 
-    def getPluginByName(self, name: str, category: str | None = None) -> PluginInfo | None:
+    def getPluginByName(self, name: str, category: Optional[str] = None) -> Optional[PluginInfo]:
+        """Get a loaded plugin by name and optionally by category. Returns None if no such plugin is loaded."""
         return self.get_plugin_by_name(name, category)
diff --git a/tests/helper.py b/tests/helper.py
index 495c3d3a5..8fbebdb45 100644
--- a/tests/helper.py
+++ b/tests/helper.py
@@ -9,21 +9,9 @@
 import pathlib
 from contextlib import contextmanager
 
-
-import nikola.utils
 import nikola.shortcodes
+import nikola.utils
 from nikola.plugin_manager import PluginManager
-from nikola.plugin_categories import (
-    Command,
-    Task,
-    LateTask,
-    TemplateSystem,
-    PageCompiler,
-    TaskMultiplier,
-    CompilerExtension,
-    MarkdownExtension,
-    RestExtension,
-)
 
 __all__ = ["cd", "FakeSite"]
 
diff --git a/tests/test_plugin_manager.py b/tests/test_plugin_manager.py
index 380e6a22c..a4039c5a2 100644
--- a/tests/test_plugin_manager.py
+++ b/tests/test_plugin_manager.py
@@ -76,7 +76,7 @@ def test_locate_plugins_finds_core_and_custom_plugins():
     assert first_plugin.source_dir == places[1]
 
     assert second_plugin.category == "ConfigPlugin"
-    assert second_plugin.compiler == None
+    assert second_plugin.compiler is None
     assert second_plugin.source_dir == places[1] / "second"