diff --git a/cylc/flow/main_loop/auto_restart.py b/cylc/flow/main_loop/auto_restart.py
index 1751e6b4a05..66aa0ebbb46 100644
--- a/cylc/flow/main_loop/auto_restart.py
+++ b/cylc/flow/main_loop/auto_restart.py
@@ -54,11 +54,12 @@
 
 Suites that are started up in no-detach mode cannot auto stop-restart on a
 different host - as it will still end up attached to the condemned host.
-Therefore, a suite in no-detach mode running on a condemned host will abort with
-a non-zero return code. The parent process should manually handle the restart of
-the suite if desired.
+Therefore, a suite in no-detach mode running on a condemned host will abort
+with a non-zero return code. The parent process should manually handle the
+restart of the suite if desired.
 
 See the ``[suite servers]`` configuration section
+
 (:ref:`global-suite-servers`) for more details.
 
 """
@@ -199,7 +200,7 @@ def _set_auto_restart(
         if restart_delay > 0:
             # Delay shutdown by a random interval to avoid many
             # suites restarting simultaneously.
-            shutdown_delay = int(random() * restart_delay)
+            shutdown_delay = int(random() * restart_delay)  # nosec
         else:
             # Un-documented feature, schedule exact restart interval for
             # testing purposes.
diff --git a/cylc/flow/main_loop/health_check.py b/cylc/flow/main_loop/health_check.py
index 57f739cb69f..1bbf9472548 100644
--- a/cylc/flow/main_loop/health_check.py
+++ b/cylc/flow/main_loop/health_check.py
@@ -12,6 +12,7 @@
 from cylc.flow import suite_files
 from cylc.flow.exceptions import CylcError, SuiteServiceFileError
 
+
 async def during(scheduler, _):
     """Perform suite health checks."""
     # 1. check if suite run dir still present - if not shutdown.
@@ -32,8 +33,7 @@ def _check_contact_file(scheduler):
             scheduler.suite)
         if contact_data != scheduler.contact_data:
             raise AssertionError('contact file modified')
-    except (AssertionError, IOError, ValueError,
-            SuiteServiceFileError) as exc:
+    except (AssertionError, IOError, ValueError, SuiteServiceFileError):
         raise CylcError(
             '%s: contact file corrupted/modified and may be left'
             % suite_files.get_contact_file(scheduler.suite)
diff --git a/cylc/flow/main_loop/log_memory.py b/cylc/flow/main_loop/log_memory.py
index 44d479ce959..e499ce2307f 100644
--- a/cylc/flow/main_loop/log_memory.py
+++ b/cylc/flow/main_loop/log_memory.py
@@ -1,5 +1,4 @@
 import json
-import math
 from pathlib import Path
 from time import time
 
@@ -72,7 +71,7 @@ def _transpose(data):
     all_keys = list(all_keys)
     all_keys.sort(key=lambda x: data[-1][1].get(x, 0), reverse=True)
 
-    # extract data for each field, if not present 
+    # extract data for each field, if not present
     fields = {}
     for key in all_keys:
         fields[key] = [
diff --git a/cylc/flow/scheduler.py b/cylc/flow/scheduler.py
index 84756f6bc2b..4720705a931 100644
--- a/cylc/flow/scheduler.py
+++ b/cylc/flow/scheduler.py
@@ -537,7 +537,7 @@ def configure(self):
                 self.config.cfg['cylc']['events'][key] = DurationFloat(180)
         if self._get_events_conf(key):
             self.set_suite_inactivity_timer()
-        
+
         # Main loop plugins
         self.main_loop_plugins = main_loop.load_plugins(
             self._get_cylc_conf('main loop', {}),
@@ -1462,7 +1462,6 @@ def suite_auto_restart(self, max_retries=3):
             'manual restart required.', max_retries)
         return False
 
-
     def update_profiler_logs(self, tinit):
         """Update info for profiler."""
         now = time()
diff --git a/cylc/flow/tests/main_loop.py b/cylc/flow/tests/main_loop.py
index 333b7e1a51e..9e05963f261 100644
--- a/cylc/flow/tests/main_loop.py
+++ b/cylc/flow/tests/main_loop.py
@@ -59,11 +59,13 @@ def test_load_plugins():
 def test_wrapper_calls_function():
     """Ensure the wrapper calls coroutines."""
     flag = False
+
     async def test_coro(arg1, arg2):
         assert arg1 == 'arg1'
         assert arg2 == 'arg2'
         nonlocal flag
         flag = True
+
     coro = _wrapper(
         test_coro,
         ('arg1', 'arg2')
@@ -132,9 +134,11 @@ async def test_coro():
 def test_before():
     """Ensure the before function calls all before coros."""
     calls = []
+
     def capture(*stuff):
         nonlocal calls
         calls.append(stuff)
+
     plugins = {
         'before': {
             'foo': capture,
@@ -154,6 +158,7 @@ def capture(*stuff):
         (42, {'c': 3}),
     ]
 
+
 @pytest.fixture
 def test_plugins():
     return {
@@ -191,14 +196,17 @@ def test_plugins():
 def test_during(test_plugins):
     """Ensure the during function calls all during and on_change coros."""
     calls = []
+
     def capture_during(_, state):
         nonlocal calls
         state['calls'].append(f'during_{state["name"]}')
         calls.append(list(state['calls']))
+
     def capture_on_change(_, state):
         nonlocal calls
         state['calls'].append(f'on_change_{state["name"]}')
         calls.append(list(state['calls']))
+
     test_plugins.update({
         'during': {
             'foo': capture_during,
@@ -221,10 +229,13 @@ def capture_on_change(_, state):
 
 
 def test_during_interval(test_plugins):
+
     def capture_during(_, state):
         state['calls'].append(f'during_{state["name"]}')
+
     def capture_on_change(_, state):
         state['calls'].append(f'on_change_{state["name"]}')
+
     test_plugins.update({
         'during': {
             'foo': capture_during,
@@ -278,9 +289,11 @@ def capture_on_change(_, state):
 def test_after():
     """Ensure the after function calls all after coros."""
     calls = []
+
     def capture(*stuff):
         nonlocal calls
         calls.append(stuff)
+
     plugins = {
         'after': {
             'foo': capture,
diff --git a/cylc/flow/tests/main_loop/auto_restart.py b/cylc/flow/tests/main_loop/auto_restart.py
index 8934d11e575..982d3d0e60a 100644
--- a/cylc/flow/tests/main_loop/auto_restart.py
+++ b/cylc/flow/tests/main_loop/auto_restart.py
@@ -179,10 +179,12 @@ def test_set_auto_restart_no_detach(caplog):
 def test_set_auto_restart_unable_to_restart(monkeypatch):
     """Ensure returns False if suite is unable to restart"""
     called = False
+
     def suite_select_fail(**_):
         nonlocal called
         called = True  # prevent this becoming a placebo
         return False
+
     monkeypatch.setattr(
         'cylc.flow.main_loop.auto_restart._can_auto_restart',
         suite_select_fail
@@ -201,10 +203,12 @@ def suite_select_fail(**_):
 def test_set_auto_restart_with_delay(monkeypatch, caplog):
     """Ensure suites wait for a period before auto-restarting."""
     called = False
+
     def suite_select_pass(**_):
         nonlocal called
         called = True  # prevent this becoming a placebo
         return True
+
     monkeypatch.setattr(
         'cylc.flow.main_loop.auto_restart._can_auto_restart',
         suite_select_pass
@@ -233,10 +237,12 @@ def suite_select_pass(**_):
 def test_set_auto_restart_without_delay(monkeypatch, caplog):
     """Ensure suites auto-restart when no delay is provided."""
     called = False
+
     def suite_select_pass(**_):
         nonlocal called
         called = True  # prevent this becoming a placebo
         return True
+
     monkeypatch.setattr(
         'cylc.flow.main_loop.auto_restart._can_auto_restart',
         suite_select_pass