Fix and enable flake8 F812

F812 list comprehension redefines

List comprehension don't have scope so redefining variables can lead to
unexpected behaviors

Change-Id: I85484dfcd4fa391195ea7be75aadc7897da4739c

nova/db/sqlalchemy/api.py

@@ -2854,18 +2854,18 @@ def quota_reserve(context, resources, quotas, deltas, expire,
                     #            a best-effort mechanism.
 
         # Check for deltas that would go negative
-        unders = [resource for resource, delta in deltas.items()
+        unders = [res for res, delta in deltas.items()
                   if delta < 0 and
-                  delta + usages[resource].in_use < 0]
+                  delta + usages[res].in_use < 0]
 
         # Now, let's check the quotas
         # NOTE(Vek): We're only concerned about positive increments.
         #            If a project has gone over quota, we want them to
         #            be able to reduce their usage without any
         #            problems.
-        overs = [resource for resource, delta in deltas.items()
-                 if quotas[resource] >= 0 and delta >= 0 and
-                 quotas[resource] < delta + usages[resource].total]
+        overs = [res for res, delta in deltas.items()
+                 if quotas[res] >= 0 and delta >= 0 and
+                 quotas[res] < delta + usages[res].total]
 
         # NOTE(Vek): The quota check needs to be in the transaction,
         #            but the transaction doesn't fail just because
@@ -2877,12 +2877,12 @@ def quota_reserve(context, resources, quotas, deltas, expire,
         # Create the reservations
         if not overs:
             reservations = []
-            for resource, delta in deltas.items():
+            for res, delta in deltas.items():
                 reservation = reservation_create(elevated,
                                                  str(uuid.uuid4()),
-                                                 usages[resource],
+                                                 usages[res],
                                                  project_id,
-                                                 resource, delta, expire,
+                                                 res, delta, expire,
                                                  session=session)
                 reservations.append(reservation.uuid)
 
@@ -2899,7 +2899,7 @@ def quota_reserve(context, resources, quotas, deltas, expire,
                 #            To prevent this, we only update the
                 #            reserved value if the delta is positive.
                 if delta > 0:
-                    usages[resource].reserved += delta
+                    usages[res].reserved += delta
 
         # Apply updates to the usages table
         for usage_ref in usages.values():

nova/tests/integrated/test_servers.py

@@ -126,7 +126,7 @@ class ServersTest(integrated_helpers._IntegratedTestBase):
 
         # It should also be in the all-servers list
         servers = self.api.get_servers()
-        server_ids = [server['id'] for server in servers]
+        server_ids = [s['id'] for s in servers]
         self.assertTrue(created_server_id in server_ids)
 
         found_server = self._wait_for_state_change(found_server, 'BUILD')

tox.ini

@@ -40,7 +40,7 @@ commands =
 commands = {posargs}
 
 [flake8]
-ignore = E12,E711,E712,H302,H303,H403,H404,F403,F811,F812,F823,F841
+ignore = E12,E711,E712,H302,H303,H403,H404,F403,F811,F823,F841
 builtins = _
 exclude =  .venv,.git,.tox,dist,doc,*openstack/common*,*lib/python*,*egg,build,plugins,tools