Clarify list/set/dict/tuple comprehensions and enforce via flake8 (#6957)

Ensure good comprehension hygiene using flake8-comprehensions.

53 files changed, 159 insertions, 168 deletions

diff --git a/synapse/app/_base.py b/synapse/app/_base.py
index 109b1e2fb5..9ffd23c6df 100644
--- a/synapse/app/_base.py
+++ b/synapse/app/_base.py
@@ -141,7 +141,7 @@ def start_reactor(
 
 def quit_with_error(error_string):
     message_lines = error_string.split("\n")
-    line_length = max([len(l) for l in message_lines if len(l) < 80]) + 2
+    line_length = max(len(l) for l in message_lines if len(l) < 80) + 2
     sys.stderr.write("*" * line_length + "\n")
     for line in message_lines:
         sys.stderr.write(" %s\n" % (line.rstrip(),))
diff --git a/synapse/app/federation_sender.py b/synapse/app/federation_sender.py
index 63a91f1177..b7fcf80ddc 100644
--- a/synapse/app/federation_sender.py
+++ b/synapse/app/federation_sender.py
@@ -262,7 +262,7 @@ class FederationSenderHandler(object):
 
         # ... as well as device updates and messages
         elif stream_name == DeviceListsStream.NAME:
-            hosts = set(row.destination for row in rows)
+            hosts = {row.destination for row in rows}
             for host in hosts:
                 self.federation_sender.send_device_messages(host)
 
@@ -270,7 +270,7 @@ class FederationSenderHandler(object):
             # The to_device stream includes stuff to be pushed to both local
             # clients and remote servers, so we ignore entities that start with
             # '@' (since they'll be local users rather than destinations).
-            hosts = set(row.entity for row in rows if not row.entity.startswith("@"))
+            hosts = {row.entity for row in rows if not row.entity.startswith("@")}
             for host in hosts:
                 self.federation_sender.send_device_messages(host)
 
diff --git a/synapse/app/pusher.py b/synapse/app/pusher.py
index e46b6ac598..84e9f8d5e2 100644
--- a/synapse/app/pusher.py
+++ b/synapse/app/pusher.py
@@ -158,7 +158,7 @@ class PusherReplicationHandler(ReplicationClientHandler):
                 yield self.pusher_pool.on_new_notifications(token, token)
             elif stream_name == "receipts":
                 yield self.pusher_pool.on_new_receipts(
-                    token, token, set(row.room_id for row in rows)
+                    token, token, {row.room_id for row in rows}
                 )
         except Exception:
             logger.exception("Error poking pushers")
diff --git a/synapse/config/server.py b/synapse/config/server.py
index 0ec1b0fadd..7525765fee 100644
--- a/synapse/config/server.py
+++ b/synapse/config/server.py
@@ -1066,12 +1066,12 @@ KNOWN_RESOURCES = (
 
 
 def _check_resource_config(listeners):
-    resource_names = set(
+    resource_names = {
         res_name
         for listener in listeners
         for res in listener.get("resources", [])
         for res_name in res.get("names", [])
-    )
+    }
 
     for resource in resource_names:
         if resource not in KNOWN_RESOURCES:
diff --git a/synapse/config/tls.py b/synapse/config/tls.py
index 97a12d51f6..a65538562b 100644
--- a/synapse/config/tls.py
+++ b/synapse/config/tls.py
@@ -260,7 +260,7 @@ class TlsConfig(Config):
                 crypto.FILETYPE_ASN1, self.tls_certificate
             )
             sha256_fingerprint = encode_base64(sha256(x509_certificate_bytes).digest())
-            sha256_fingerprints = set(f["sha256"] for f in self.tls_fingerprints)
+            sha256_fingerprints = {f["sha256"] for f in self.tls_fingerprints}
             if sha256_fingerprint not in sha256_fingerprints:
                 self.tls_fingerprints.append({"sha256": sha256_fingerprint})
 
diff --git a/synapse/crypto/keyring.py b/synapse/crypto/keyring.py
index 6fe5a6a26a..983f0ead8c 100644
--- a/synapse/crypto/keyring.py
+++ b/synapse/crypto/keyring.py
@@ -326,9 +326,7 @@ class Keyring(object):
             verify_requests (list[VerifyJsonRequest]): list of verify requests
         """
 
-        remaining_requests = set(
-            (rq for rq in verify_requests if not rq.key_ready.called)
-        )
+        remaining_requests = {rq for rq in verify_requests if not rq.key_ready.called}
 
         @defer.inlineCallbacks
         def do_iterations():
@@ -396,7 +394,7 @@ class Keyring(object):
 
         results = yield fetcher.get_keys(missing_keys)
 
-        completed = list()
+        completed = []
         for verify_request in remaining_requests:
             server_name = verify_request.server_name
 
diff --git a/synapse/federation/send_queue.py b/synapse/federation/send_queue.py
index 001bb304ae..876fb0e245 100644
--- a/synapse/federation/send_queue.py
+++ b/synapse/federation/send_queue.py
@@ -129,9 +129,9 @@ class FederationRemoteSendQueue(object):
             for key in keys[:i]:
                 del self.presence_changed[key]
 
-            user_ids = set(
+            user_ids = {
                 user_id for uids in self.presence_changed.values() for user_id in uids
-            )
+            }
 
             keys = self.presence_destinations.keys()
             i = self.presence_destinations.bisect_left(position_to_delete)
diff --git a/synapse/groups/groups_server.py b/synapse/groups/groups_server.py
index c106abae21..4f0dc0a209 100644
--- a/synapse/groups/groups_server.py
+++ b/synapse/groups/groups_server.py
@@ -608,7 +608,7 @@ class GroupsServerHandler(GroupsServerWorkerHandler):
         user_results = yield self.store.get_users_in_group(
             group_id, include_private=True
         )
-        if user_id in [user_result["user_id"] for user_result in user_results]:
+        if user_id in (user_result["user_id"] for user_result in user_results):
             raise SynapseError(400, "User already in group")
 
         content = {
diff --git a/synapse/handlers/device.py b/synapse/handlers/device.py
index 50cea3f378..a514c30714 100644
--- a/synapse/handlers/device.py
+++ b/synapse/handlers/device.py
@@ -742,6 +742,6 @@ class DeviceListUpdater(object):
 
         # We clobber the seen updates since we've re-synced from a given
         # point.
-        self._seen_updates[user_id] = set([stream_id])
+        self._seen_updates[user_id] = {stream_id}
 
         defer.returnValue(result)
diff --git a/synapse/handlers/directory.py b/synapse/handlers/directory.py
index 921d887b24..0b23ca919a 100644
--- a/synapse/handlers/directory.py
+++ b/synapse/handlers/directory.py
@@ -72,7 +72,7 @@ class DirectoryHandler(BaseHandler):
         # TODO(erikj): Check if there is a current association.
         if not servers:
             users = yield self.state.get_current_users_in_room(room_id)
-            servers = set(get_domain_from_id(u) for u in users)
+            servers = {get_domain_from_id(u) for u in users}
 
         if not servers:
             raise SynapseError(400, "Failed to get server list")
@@ -255,7 +255,7 @@ class DirectoryHandler(BaseHandler):
             )
 
         users = yield self.state.get_current_users_in_room(room_id)
-        extra_servers = set(get_domain_from_id(u) for u in users)
+        extra_servers = {get_domain_from_id(u) for u in users}
         servers = set(extra_servers) | set(servers)
 
         # If this server is in the list of servers, return it first.
diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index eb20ef4aec..a689065f89 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -659,11 +659,11 @@ class FederationHandler(BaseHandler):
         # this can happen if a remote server claims that the state or
         # auth_events at an event in room A are actually events in room B
 
-        bad_events = list(
+        bad_events = [
             (event_id, event.room_id)
             for event_id, event in fetched_events.items()
             if event.room_id != room_id
-        )
+        ]
 
         for bad_event_id, bad_room_id in bad_events:
             # This is a bogus situation, but since we may only discover it a long time
@@ -856,7 +856,7 @@ class FederationHandler(BaseHandler):
 
         # Don't bother processing events we already have.
         seen_events = await self.store.have_events_in_timeline(
-            set(e.event_id for e in events)
+            {e.event_id for e in events}
         )
 
         events = [e for e in events if e.event_id not in seen_events]
@@ -866,7 +866,7 @@ class FederationHandler(BaseHandler):
 
         event_map = {e.event_id: e for e in events}
 
-        event_ids = set(e.event_id for e in events)
+        event_ids = {e.event_id for e in events}
 
         # build a list of events whose prev_events weren't in the batch.
         # (XXX: this will include events whose prev_events we already have; that doesn't
@@ -892,13 +892,13 @@ class FederationHandler(BaseHandler):
             state_events.update({s.event_id: s for s in state})
             events_to_state[e_id] = state
 
-        required_auth = set(
+        required_auth = {
             a_id
             for event in events
             + list(state_events.values())
             + list(auth_events.values())
             for a_id in event.auth_event_ids()
-        )
+        }
         auth_events.update(
             {e_id: event_map[e_id] for e_id in required_auth if e_id in event_map}
         )
@@ -1247,7 +1247,7 @@ class FederationHandler(BaseHandler):
     async def on_event_auth(self, event_id: str) -> List[EventBase]:
         event = await self.store.get_event(event_id)
         auth = await self.store.get_auth_chain(
-            [auth_id for auth_id in event.auth_event_ids()], include_given=True
+            list(event.auth_event_ids()), include_given=True
         )
         return list(auth)
 
@@ -2152,7 +2152,7 @@ class FederationHandler(BaseHandler):
 
         # Now get the current auth_chain for the event.
         local_auth_chain = await self.store.get_auth_chain(
-            [auth_id for auth_id in event.auth_event_ids()], include_given=True
+            list(event.auth_event_ids()), include_given=True
         )
 
         # TODO: Check if we would now reject event_id. If so we need to tell
@@ -2654,7 +2654,7 @@ class FederationHandler(BaseHandler):
             member_handler = self.hs.get_room_member_handler()
             yield member_handler.send_membership_event(None, event, context)
         else:
-            destinations = set(x.split(":", 1)[-1] for x in (sender_user_id, room_id))
+            destinations = {x.split(":", 1)[-1] for x in (sender_user_id, room_id)}
             yield self.federation_client.forward_third_party_invite(
                 destinations, room_id, event_dict
             )
diff --git a/synapse/handlers/presence.py b/synapse/handlers/presence.py
index 202aa9294f..0d6cf2b008 100644
--- a/synapse/handlers/presence.py
+++ b/synapse/handlers/presence.py
@@ -313,7 +313,7 @@ class PresenceHandler(object):
                 notified_presence_counter.inc(len(to_notify))
                 yield self._persist_and_notify(list(to_notify.values()))
 
-            self.unpersisted_users_changes |= set(s.user_id for s in new_states)
+            self.unpersisted_users_changes |= {s.user_id for s in new_states}
             self.unpersisted_users_changes -= set(to_notify.keys())
 
             to_federation_ping = {
@@ -698,7 +698,7 @@ class PresenceHandler(object):
         updates = yield self.current_state_for_users(target_user_ids)
         updates = list(updates.values())
 
-        for user_id in set(target_user_ids) - set(u.user_id for u in updates):
+        for user_id in set(target_user_ids) - {u.user_id for u in updates}:
             updates.append(UserPresenceState.default(user_id))
 
         now = self.clock.time_msec()
@@ -886,7 +886,7 @@ class PresenceHandler(object):
             hosts = yield self.state.get_current_hosts_in_room(room_id)
 
             # Filter out ourselves.
-            hosts = set(host for host in hosts if host != self.server_name)
+            hosts = {host for host in hosts if host != self.server_name}
 
             self.federation.send_presence_to_destinations(
                 states=[state], destinations=hosts
diff --git a/synapse/handlers/receipts.py b/synapse/handlers/receipts.py
index 9283c039e3..8bc100db42 100644
--- a/synapse/handlers/receipts.py
+++ b/synapse/handlers/receipts.py
@@ -94,7 +94,7 @@ class ReceiptsHandler(BaseHandler):
             # no new receipts
             return False
 
-        affected_room_ids = list(set([r.room_id for r in receipts]))
+        affected_room_ids = list({r.room_id for r in receipts})
 
         self.notifier.on_new_event("receipt_key", max_batch_id, rooms=affected_room_ids)
         # Note that the min here shouldn't be relied upon to be accurate.
diff --git a/synapse/handlers/room.py b/synapse/handlers/room.py
index 76e8f61b74..8ee870f0bb 100644
--- a/synapse/handlers/room.py
+++ b/synapse/handlers/room.py
@@ -355,7 +355,7 @@ class RoomCreationHandler(BaseHandler):
             # If so, mark the new room as non-federatable as well
             creation_content["m.federate"] = False
 
-        initial_state = dict()
+        initial_state = {}
 
         # Replicate relevant room events
         types_to_copy = (
diff --git a/synapse/handlers/search.py b/synapse/handlers/search.py
index 110097eab9..ec1542d416 100644
--- a/synapse/handlers/search.py
+++ b/synapse/handlers/search.py
@@ -184,7 +184,7 @@ class SearchHandler(BaseHandler):
             membership_list=[Membership.JOIN],
             # membership_list=[Membership.JOIN, Membership.LEAVE, Membership.Ban],
         )
-        room_ids = set(r.room_id for r in rooms)
+        room_ids = {r.room_id for r in rooms}
 
         # If doing a subset of all rooms seearch, check if any of the rooms
         # are from an upgraded room, and search their contents as well
@@ -374,12 +374,12 @@ class SearchHandler(BaseHandler):
                 ).to_string()
 
                 if include_profile:
-                    senders = set(
+                    senders = {
                         ev.sender
                         for ev in itertools.chain(
                             res["events_before"], [event], res["events_after"]
                         )
-                    )
+                    }
 
                     if res["events_after"]:
                         last_event_id = res["events_after"][-1].event_id
@@ -421,7 +421,7 @@ class SearchHandler(BaseHandler):
 
         state_results = {}
         if include_state:
-            rooms = set(e.room_id for e in allowed_events)
+            rooms = {e.room_id for e in allowed_events}
             for room_id in rooms:
                 state = yield self.state_handler.get_current_state(room_id)
                 state_results[room_id] = list(state.values())
diff --git a/synapse/handlers/sync.py b/synapse/handlers/sync.py
index 4324bc702e..669dbc8a48 100644
--- a/synapse/handlers/sync.py
+++ b/synapse/handlers/sync.py
@@ -682,11 +682,9 @@ class SyncHandler(object):
 
         # FIXME: order by stream ordering rather than as returned by SQL
         if joined_user_ids or invited_user_ids:
-            summary["m.heroes"] = sorted(
-                [user_id for user_id in (joined_user_ids + invited_user_ids)]
-            )[0:5]
+            summary["m.heroes"] = sorted(joined_user_ids + invited_user_ids)[0:5]
         else:
-            summary["m.heroes"] = sorted([user_id for user_id in gone_user_ids])[0:5]
+            summary["m.heroes"] = sorted(gone_user_ids)[0:5]
 
         if not sync_config.filter_collection.lazy_load_members():
             return summary
@@ -697,9 +695,9 @@ class SyncHandler(object):
 
         # track which members the client should already know about via LL:
         # Ones which are already in state...
-        existing_members = set(
+        existing_members = {
             user_id for (typ, user_id) in state.keys() if typ == EventTypes.Member
-        )
+        }
 
         # ...or ones which are in the timeline...
         for ev in batch.events:
@@ -773,10 +771,10 @@ class SyncHandler(object):
                 # We only request state for the members needed to display the
                 # timeline:
 
-                members_to_fetch = set(
+                members_to_fetch = {
                     event.sender  # FIXME: we also care about invite targets etc.
                     for event in batch.events
-                )
+                }
 
                 if full_state:
                     # always make sure we LL ourselves so we know we're in the room
@@ -1993,10 +1991,10 @@ def _calculate_state(
         )
     }
 
-    c_ids = set(e for e in itervalues(current))
-    ts_ids = set(e for e in itervalues(timeline_start))
-    p_ids = set(e for e in itervalues(previous))
-    tc_ids = set(e for e in itervalues(timeline_contains))
+    c_ids = set(itervalues(current))
+    ts_ids = set(itervalues(timeline_start))
+    p_ids = set(itervalues(previous))
+    tc_ids = set(itervalues(timeline_contains))
 
     # If we are lazyloading room members, we explicitly add the membership events
     # for the senders in the timeline into the state block returned by /sync,
diff --git a/synapse/handlers/typing.py b/synapse/handlers/typing.py
index 5406618431..391bceb0c4 100644
--- a/synapse/handlers/typing.py
+++ b/synapse/handlers/typing.py
@@ -198,7 +198,7 @@ class TypingHandler(object):
                 now=now, obj=member, then=now + FEDERATION_PING_INTERVAL
             )
 
-            for domain in set(get_domain_from_id(u) for u in users):
+            for domain in {get_domain_from_id(u) for u in users}:
                 if domain != self.server_name:
                     logger.debug("sending typing update to %s", domain)
                     self.federation.build_and_send_edu(
@@ -231,7 +231,7 @@ class TypingHandler(object):
             return
 
         users = yield self.state.get_current_users_in_room(room_id)
-        domains = set(get_domain_from_id(u) for u in users)
+        domains = {get_domain_from_id(u) for u in users}
 
         if self.server_name in domains:
             logger.info("Got typing update from %s: %r", user_id, content)
diff --git a/synapse/logging/utils.py b/synapse/logging/utils.py
index 6073fc2725..0c2527bd86 100644
--- a/synapse/logging/utils.py
+++ b/synapse/logging/utils.py
@@ -148,7 +148,7 @@ def trace_function(f):
             pathname=pathname,
             lineno=lineno,
             msg=msg,
-            args=tuple(),
+            args=(),
             exc_info=None,
         )
 
diff --git a/synapse/metrics/__init__.py b/synapse/metrics/__init__.py
index 0b45e1f52a..0dba997a23 100644
--- a/synapse/metrics/__init__.py
+++ b/synapse/metrics/__init__.py
@@ -240,7 +240,7 @@ class BucketCollector(object):
         res.append(["+Inf", sum(data.values())])
 
         metric = HistogramMetricFamily(
-            self.name, "", buckets=res, sum_value=sum([x * y for x, y in data.items()])
+            self.name, "", buckets=res, sum_value=sum(x * y for x, y in data.items())
         )
         yield metric
 
diff --git a/synapse/metrics/background_process_metrics.py b/synapse/metrics/background_process_metrics.py
index c53d2a0d40..b65bcd8806 100644
--- a/synapse/metrics/background_process_metrics.py
+++ b/synapse/metrics/background_process_metrics.py
@@ -80,13 +80,13 @@ _background_process_db_sched_duration = Counter(
 # map from description to a counter, so that we can name our logcontexts
 # incrementally. (It actually duplicates _background_process_start_count, but
 # it's much simpler to do so than to try to combine them.)
-_background_process_counts = dict()  # type: dict[str, int]
+_background_process_counts = {}  # type: dict[str, int]
 
 # map from description to the currently running background processes.
 #
 # it's kept as a dict of sets rather than a big set so that we can keep track
 # of process descriptions that no longer have any active processes.
-_background_processes = dict()  # type: dict[str, set[_BackgroundProcess]]
+_background_processes = {}  # type: dict[str, set[_BackgroundProcess]]
 
 # A lock that covers the above dicts
 _bg_metrics_lock = threading.Lock()
diff --git a/synapse/push/bulk_push_rule_evaluator.py b/synapse/push/bulk_push_rule_evaluator.py
index 7d9f5a38d9..433ca2f416 100644
--- a/synapse/push/bulk_push_rule_evaluator.py
+++ b/synapse/push/bulk_push_rule_evaluator.py
@@ -400,11 +400,11 @@ class RulesForRoom(object):
         if logger.isEnabledFor(logging.DEBUG):
             logger.debug("Found members %r: %r", self.room_id, members.values())
 
-        interested_in_user_ids = set(
+        interested_in_user_ids = {
             user_id
             for user_id, membership in itervalues(members)
             if membership == Membership.JOIN
-        )
+        }
 
         logger.debug("Joined: %r", interested_in_user_ids)
 
@@ -412,9 +412,9 @@ class RulesForRoom(object):
             interested_in_user_ids, on_invalidate=self.invalidate_all_cb
         )
 
-        user_ids = set(
+        user_ids = {
             uid for uid, have_pusher in iteritems(if_users_with_pushers) if have_pusher
-        )
+        }
 
         logger.debug("With pushers: %r", user_ids)
 
diff --git a/synapse/push/emailpusher.py b/synapse/push/emailpusher.py
index 8c818a86bf..ba4551d619 100644
--- a/synapse/push/emailpusher.py
+++ b/synapse/push/emailpusher.py
@@ -204,7 +204,7 @@ class EmailPusher(object):
                 yield self.send_notification(unprocessed, reason)
 
                 yield self.save_last_stream_ordering_and_success(
-                    max([ea["stream_ordering"] for ea in unprocessed])
+                    max(ea["stream_ordering"] for ea in unprocessed)
                 )
 
                 # we update the throttle on all the possible unprocessed push actions
diff --git a/synapse/push/mailer.py b/synapse/push/mailer.py
index b13b646bfd..4ccaf178ce 100644
--- a/synapse/push/mailer.py
+++ b/synapse/push/mailer.py
@@ -526,12 +526,10 @@ class Mailer(object):
                     # If the room doesn't have a name, say who the messages
                     # are from explicitly to avoid, "messages in the Bob room"
                     sender_ids = list(
-                        set(
-                            [
-                                notif_events[n["event_id"]].sender
-                                for n in notifs_by_room[room_id]
-                            ]
-                        )
+                        {
+                            notif_events[n["event_id"]].sender
+                            for n in notifs_by_room[room_id]
+                        }
                     )
 
                     member_events = yield self.store.get_events(
@@ -558,12 +556,10 @@ class Mailer(object):
                 # If the reason room doesn't have a name, say who the messages
                 # are from explicitly to avoid, "messages in the Bob room"
                 sender_ids = list(
-                    set(
-                        [
-                            notif_events[n["event_id"]].sender
-                            for n in notifs_by_room[reason["room_id"]]
-                        ]
-                    )
+                    {
+                        notif_events[n["event_id"]].sender
+                        for n in notifs_by_room[reason["room_id"]]
+                    }
                 )
 
                 member_events = yield self.store.get_events(
diff --git a/synapse/push/pusherpool.py b/synapse/push/pusherpool.py
index b9dca5bc63..01789a9fb4 100644
--- a/synapse/push/pusherpool.py
+++ b/synapse/push/pusherpool.py
@@ -191,7 +191,7 @@ class PusherPool:
                 min_stream_id - 1, max_stream_id
             )
             # This returns a tuple, user_id is at index 3
-            users_affected = set([r[3] for r in updated_receipts])
+            users_affected = {r[3] for r in updated_receipts}
 
             for u in users_affected:
                 if u in self.pushers:
diff --git a/synapse/rest/admin/_base.py b/synapse/rest/admin/_base.py
index 459482eb6d..a96f75ce26 100644
--- a/synapse/rest/admin/_base.py
+++ b/synapse/rest/admin/_base.py
@@ -29,7 +29,7 @@ def historical_admin_path_patterns(path_regex):
     Note that this should only be used for existing endpoints: new ones should just
     register for the /_synapse/admin path.
     """
-    return list(
+    return [
         re.compile(prefix + path_regex)
         for prefix in (
             "^/_synapse/admin/v1",
@@ -37,7 +37,7 @@ def historical_admin_path_patterns(path_regex):
             "^/_matrix/client/unstable/admin",
             "^/_matrix/client/r0/admin",
         )
-    )
+    ]
 
 
 def admin_patterns(path_regex: str):
diff --git a/synapse/rest/client/v1/push_rule.py b/synapse/rest/client/v1/push_rule.py
index 4f74600239..9fd4908136 100644
--- a/synapse/rest/client/v1/push_rule.py
+++ b/synapse/rest/client/v1/push_rule.py
@@ -49,7 +49,7 @@ class PushRuleRestServlet(RestServlet):
         if self._is_worker:
             raise Exception("Cannot handle PUT /push_rules on worker")
 
-        spec = _rule_spec_from_path([x for x in path.split("/")])
+        spec = _rule_spec_from_path(path.split("/"))
         try:
             priority_class = _priority_class_from_spec(spec)
         except InvalidRuleException as e:
@@ -110,7 +110,7 @@ class PushRuleRestServlet(RestServlet):
         if self._is_worker:
             raise Exception("Cannot handle DELETE /push_rules on worker")
 
-        spec = _rule_spec_from_path([x for x in path.split("/")])
+        spec = _rule_spec_from_path(path.split("/"))
 
         requester = await self.auth.get_user_by_req(request)
         user_id = requester.user.to_string()
@@ -138,7 +138,7 @@ class PushRuleRestServlet(RestServlet):
 
         rules = format_push_rules_for_user(requester.user, rules)
 
-        path = [x for x in path.split("/")][1:]
+        path = path.split("/")[1:]
 
         if path == []:
             # we're a reference impl: pedantry is our job.
diff --git a/synapse/rest/client/v1/pusher.py b/synapse/rest/client/v1/pusher.py
index 6f6b7aed6e..550a2f1b44 100644
--- a/synapse/rest/client/v1/pusher.py
+++ b/synapse/rest/client/v1/pusher.py
@@ -54,9 +54,9 @@ class PushersRestServlet(RestServlet):
 
         pushers = await self.hs.get_datastore().get_pushers_by_user_id(user.to_string())
 
-        filtered_pushers = list(
+        filtered_pushers = [
             {k: v for k, v in p.items() if k in ALLOWED_KEYS} for p in pushers
-        )
+        ]
 
         return 200, {"pushers": filtered_pushers}
 
diff --git a/synapse/rest/client/v2_alpha/sync.py b/synapse/rest/client/v2_alpha/sync.py
index d8292ce29f..8fa68dd37f 100644
--- a/synapse/rest/client/v2_alpha/sync.py
+++ b/synapse/rest/client/v2_alpha/sync.py
@@ -72,7 +72,7 @@ class SyncRestServlet(RestServlet):
     """
 
     PATTERNS = client_patterns("/sync$")
-    ALLOWED_PRESENCE = set(["online", "offline", "unavailable"])
+    ALLOWED_PRESENCE = {"online", "offline", "unavailable"}
 
     def __init__(self, hs):
         super(SyncRestServlet, self).__init__()
diff --git a/synapse/rest/key/v2/remote_key_resource.py b/synapse/rest/key/v2/remote_key_resource.py
index 9d6813a047..4b6d030a57 100644
--- a/synapse/rest/key/v2/remote_key_resource.py
+++ b/synapse/rest/key/v2/remote_key_resource.py
@@ -149,7 +149,7 @@ class RemoteKey(DirectServeResource):
 
         time_now_ms = self.clock.time_msec()
 
-        cache_misses = dict()  # type: Dict[str, Set[str]]
+        cache_misses = {}  # type: Dict[str, Set[str]]
         for (server_name, key_id, from_server), results in cached.items():
             results = [(result["ts_added_ms"], result) for result in results]
 
diff --git a/synapse/rest/media/v1/_base.py b/synapse/rest/media/v1/_base.py
index 65bbf00073..ba28dd089d 100644
--- a/synapse/rest/media/v1/_base.py
+++ b/synapse/rest/media/v1/_base.py
@@ -135,27 +135,25 @@ def add_file_headers(request, media_type, file_size, upload_name):
 
 # separators as defined in RFC2616. SP and HT are handled separately.
 # see _can_encode_filename_as_token.
-_FILENAME_SEPARATOR_CHARS = set(
-    (
-        "(",
-        ")",
-        "<",
-        ">",
-        "@",
-        ",",
-        ";",
-        ":",
-        "\\",
-        '"',
-        "/",
-        "[",
-        "]",
-        "?",
-        "=",
-        "{",
-        "}",
-    )
-)
+_FILENAME_SEPARATOR_CHARS = {
+    "(",
+    ")",
+    "<",
+    ">",
+    "@",
+    ",",
+    ";",
+    ":",
+    "\\",
+    '"',
+    "/",
+    "[",
+    "]",
+    "?",
+    "=",
+    "{",
+    "}",
+}
 
 
 def _can_encode_filename_as_token(x):
diff --git a/synapse/state/v1.py b/synapse/state/v1.py
index 24b7c0faef..9bf98d06f2 100644
--- a/synapse/state/v1.py
+++ b/synapse/state/v1.py
@@ -69,9 +69,9 @@ def resolve_events_with_store(
 
     unconflicted_state, conflicted_state = _seperate(state_sets)
 
-    needed_events = set(
+    needed_events = {
         event_id for event_ids in itervalues(conflicted_state) for event_id in event_ids
-    )
+    }
     needed_event_count = len(needed_events)
     if event_map is not None:
         needed_events -= set(iterkeys(event_map))
@@ -261,11 +261,11 @@ def _resolve_state_events(conflicted_state, auth_events):
 
 
 def _resolve_auth_events(events, auth_events):
-    reverse = [i for i in reversed(_ordered_events(events))]
+    reverse = list(reversed(_ordered_events(events)))
 
-    auth_keys = set(
+    auth_keys = {
         key for event in events for key in event_auth.auth_types_for_event(event)
-    )
+    }
 
     new_auth_events = {}
     for key in auth_keys:
diff --git a/synapse/state/v2.py b/synapse/state/v2.py
index 75fe58305a..0ffe6d8c14 100644
--- a/synapse/state/v2.py
+++ b/synapse/state/v2.py
@@ -105,7 +105,7 @@ def resolve_events_with_store(
                 % (room_id, event.event_id, event.room_id,)
             )
 
-    full_conflicted_set = set(eid for eid in full_conflicted_set if eid in event_map)
+    full_conflicted_set = {eid for eid in full_conflicted_set if eid in event_map}
 
     logger.debug("%d full_conflicted_set entries", len(full_conflicted_set))
 
@@ -233,7 +233,7 @@ def _get_auth_chain_difference(state_sets, event_map, state_res_store):
 
     auth_sets = []
     for state_set in state_sets:
-        auth_ids = set(
+        auth_ids = {
             eid
             for key, eid in iteritems(state_set)
             if (
@@ -246,7 +246,7 @@ def _get_auth_chain_difference(state_sets, event_map, state_res_store):
                 )
             )
             and eid not in common
-        )
+        }
 
         auth_chain = yield state_res_store.get_auth_chain(auth_ids, common)
         auth_ids.update(auth_chain)
@@ -275,7 +275,7 @@ def _seperate(state_sets):
     conflicted_state = {}
 
     for key in set(itertools.chain.from_iterable(state_sets)):
-        event_ids = set(state_set.get(key) for state_set in state_sets)
+        event_ids = {state_set.get(key) for state_set in state_sets}
         if len(event_ids) == 1:
             unconflicted_state[key] = event_ids.pop()
         else:
diff --git a/synapse/storage/_base.py b/synapse/storage/_base.py
index da3b99f93d..13de5f1f62 100644
--- a/synapse/storage/_base.py
+++ b/synapse/storage/_base.py
@@ -56,7 +56,7 @@ class SQLBaseStore(metaclass=ABCMeta):
             members_changed (iterable[str]): The user_ids of members that have
                 changed
         """
-        for host in set(get_domain_from_id(u) for u in members_changed):
+        for host in {get_domain_from_id(u) for u in members_changed}:
             self._attempt_to_invalidate_cache("is_host_joined", (room_id, host))
             self._attempt_to_invalidate_cache("was_host_joined", (room_id, host))
 
diff --git a/synapse/storage/background_updates.py b/synapse/storage/background_updates.py
index bd547f35cf..eb1a7e5002 100644
--- a/synapse/storage/background_updates.py
+++ b/synapse/storage/background_updates.py
@@ -189,7 +189,7 @@ class BackgroundUpdater(object):
                 keyvalues=None,
                 retcols=("update_name", "depends_on"),
             )
-            in_flight = set(update["update_name"] for update in updates)
+            in_flight = {update["update_name"] for update in updates}
             for update in updates:
                 if update["depends_on"] not in in_flight:
                     self._background_update_queue.append(update["update_name"])
diff --git a/synapse/storage/data_stores/main/appservice.py b/synapse/storage/data_stores/main/appservice.py
index b2f39649fd..efbc06c796 100644
--- a/synapse/storage/data_stores/main/appservice.py
+++ b/synapse/storage/data_stores/main/appservice.py
@@ -135,7 +135,7 @@ class ApplicationServiceTransactionWorkerStore(
             may be empty.
         """
         results = yield self.db.simple_select_list(
-            "application_services_state", dict(state=state), ["as_id"]
+            "application_services_state", {"state": state}, ["as_id"]
         )
         # NB: This assumes this class is linked with ApplicationServiceStore
         as_list = self.get_app_services()
@@ -158,7 +158,7 @@ class ApplicationServiceTransactionWorkerStore(
         """
         result = yield self.db.simple_select_one(
             "application_services_state",
-            dict(as_id=service.id),
+            {"as_id": service.id},
             ["state"],
             allow_none=True,
             desc="get_appservice_state",
@@ -177,7 +177,7 @@ class ApplicationServiceTransactionWorkerStore(
             A Deferred which resolves when the state was set successfully.
         """
         return self.db.simple_upsert(
-            "application_services_state", dict(as_id=service.id), dict(state=state)
+            "application_services_state", {"as_id": service.id}, {"state": state}
         )
 
     def create_appservice_txn(self, service, events):
@@ -253,13 +253,15 @@ class ApplicationServiceTransactionWorkerStore(
             self.db.simple_upsert_txn(
                 txn,
                 "application_services_state",
-                dict(as_id=service.id),
-                dict(last_txn=txn_id),
+                {"as_id": service.id},
+                {"last_txn": txn_id},
             )
 
             # Delete txn
             self.db.simple_delete_txn(
-                txn, "application_services_txns", dict(txn_id=txn_id, as_id=service.id)
+                txn,
+                "application_services_txns",
+                {"txn_id": txn_id, "as_id": service.id},
             )
 
         return self.db.runInteraction(
diff --git a/synapse/storage/data_stores/main/client_ips.py b/synapse/storage/data_stores/main/client_ips.py
index 13f4c9c72e..e1ccb27142 100644
--- a/synapse/storage/data_stores/main/client_ips.py
+++ b/synapse/storage/data_stores/main/client_ips.py
@@ -530,7 +530,7 @@ class ClientIpStore(ClientIpBackgroundUpdateStore):
             ((row["access_token"], row["ip"]), (row["user_agent"], row["last_seen"]))
             for row in rows
         )
-        return list(
+        return [
             {
                 "access_token": access_token,
                 "ip": ip,
@@ -538,7 +538,7 @@ class ClientIpStore(ClientIpBackgroundUpdateStore):
                 "last_seen": last_seen,
             }
             for (access_token, ip), (user_agent, last_seen) in iteritems(results)
-        )
+        ]
 
     @wrap_as_background_process("prune_old_user_ips")
     async def _prune_old_user_ips(self):
diff --git a/synapse/storage/data_stores/main/devices.py b/synapse/storage/data_stores/main/devices.py
index b7617efb80..d55733a4cd 100644
--- a/synapse/storage/data_stores/main/devices.py
+++ b/synapse/storage/data_stores/main/devices.py
@@ -137,7 +137,7 @@ class DeviceWorkerStore(SQLBaseStore):
 
         # get the cross-signing keys of the users in the list, so that we can
         # determine which of the device changes were cross-signing keys
-        users = set(r[0] for r in updates)
+        users = {r[0] for r in updates}
         master_key_by_user = {}
         self_signing_key_by_user = {}
         for user in users:
@@ -446,7 +446,7 @@ class DeviceWorkerStore(SQLBaseStore):
             a set of user_ids and results_map is a mapping of
             user_id -> device_id -> device_info
         """
-        user_ids = set(user_id for user_id, _ in query_list)
+        user_ids = {user_id for user_id, _ in query_list}
         user_map = yield self.get_device_list_last_stream_id_for_remotes(list(user_ids))
 
         # We go and check if any of the users need to have their device lists
@@ -454,10 +454,9 @@ class DeviceWorkerStore(SQLBaseStore):
         users_needing_resync = yield self.get_user_ids_requiring_device_list_resync(
             user_ids
         )
-        user_ids_in_cache = (
-            set(user_id for user_id, stream_id in user_map.items() if stream_id)
-            - users_needing_resync
-        )
+        user_ids_in_cache = {
+            user_id for user_id, stream_id in user_map.items() if stream_id
+        } - users_needing_resync
         user_ids_not_in_cache = user_ids - user_ids_in_cache
 
         results = {}
@@ -604,7 +603,7 @@ class DeviceWorkerStore(SQLBaseStore):
             rows = yield self.db.execute(
                 "get_users_whose_signatures_changed", None, sql, user_id, from_key
             )
-            return set(user for row in rows for user in json.loads(row[0]))
+            return {user for row in rows for user in json.loads(row[0])}
         else:
             return set()
 
diff --git a/synapse/storage/data_stores/main/event_federation.py b/synapse/storage/data_stores/main/event_federation.py
index 750ec1b70d..49a7b8b433 100644
--- a/synapse/storage/data_stores/main/event_federation.py
+++ b/synapse/storage/data_stores/main/event_federation.py
@@ -426,7 +426,7 @@ class EventFederationWorkerStore(EventsWorkerStore, SignatureWorkerStore, SQLBas
                     query, (room_id, event_id, False, limit - len(event_results))
                 )
 
-                new_results = set(t[0] for t in txn) - seen_events
+                new_results = {t[0] for t in txn} - seen_events
 
                 new_front |= new_results
                 seen_events |= new_results
diff --git a/synapse/storage/data_stores/main/events.py b/synapse/storage/data_stores/main/events.py
index c9d0d68c3a..8ae23df00a 100644
--- a/synapse/storage/data_stores/main/events.py
+++ b/synapse/storage/data_stores/main/events.py
@@ -145,7 +145,7 @@ class EventsStore(
             return txn.fetchall()
 
         res = yield self.db.runInteraction("read_forward_extremities", fetch)
-        self._current_forward_extremities_amount = c_counter(list(x[0] for x in res))
+        self._current_forward_extremities_amount = c_counter([x[0] for x in res])
 
     @_retry_on_integrity_error
     @defer.inlineCallbacks
@@ -598,11 +598,11 @@ class EventsStore(
             # We find out which membership events we may have deleted
             # and which we have added, then we invlidate the caches for all
             # those users.
-            members_changed = set(
+            members_changed = {
                 state_key
                 for ev_type, state_key in itertools.chain(to_delete, to_insert)
                 if ev_type == EventTypes.Member
-            )
+            }
 
             for member in members_changed:
                 txn.call_after(
@@ -1615,7 +1615,7 @@ class EventsStore(
         """
         )
 
-        referenced_state_groups = set(sg for sg, in txn)
+        referenced_state_groups = {sg for sg, in txn}
         logger.info(
             "[purge] found %i referenced state groups", len(referenced_state_groups)
         )
diff --git a/synapse/storage/data_stores/main/events_bg_updates.py b/synapse/storage/data_stores/main/events_bg_updates.py
index 5177b71016..f54c8b1ee0 100644
--- a/synapse/storage/data_stores/main/events_bg_updates.py
+++ b/synapse/storage/data_stores/main/events_bg_updates.py
@@ -402,7 +402,7 @@ class EventsBackgroundUpdatesStore(SQLBaseStore):
                     keyvalues={},
                     retcols=("room_id",),
                 )
-                room_ids = set(row["room_id"] for row in rows)
+                room_ids = {row["room_id"] for row in rows}
                 for room_id in room_ids:
                     txn.call_after(
                         self.get_latest_event_ids_in_room.invalidate, (room_id,)
diff --git a/synapse/storage/data_stores/main/events_worker.py b/synapse/storage/data_stores/main/events_worker.py
index 7251e819f5..47a3a26072 100644
--- a/synapse/storage/data_stores/main/events_worker.py
+++ b/synapse/storage/data_stores/main/events_worker.py
@@ -494,9 +494,9 @@ class EventsWorkerStore(SQLBaseStore):
         """
         with Measure(self._clock, "_fetch_event_list"):
             try:
-                events_to_fetch = set(
+                events_to_fetch = {
                     event_id for events, _ in event_list for event_id in events
-                )
+                }
 
                 row_dict = self.db.new_transaction(
                     conn, "do_fetch", [], [], self._fetch_event_rows, events_to_fetch
@@ -804,7 +804,7 @@ class EventsWorkerStore(SQLBaseStore):
             desc="have_events_in_timeline",
         )
 
-        return set(r["event_id"] for r in rows)
+        return {r["event_id"] for r in rows}
 
     @defer.inlineCallbacks
     def have_seen_events(self, event_ids):
diff --git a/synapse/storage/data_stores/main/push_rule.py b/synapse/storage/data_stores/main/push_rule.py
index e2673ae073..62ac88d9f2 100644
--- a/synapse/storage/data_stores/main/push_rule.py
+++ b/synapse/storage/data_stores/main/push_rule.py
@@ -276,21 +276,21 @@ class PushRulesWorkerStore(
         # We ignore app service users for now. This is so that we don't fill
         # up the `get_if_users_have_pushers` cache with AS entries that we
         # know don't have pushers, nor even read receipts.
-        local_users_in_room = set(
+        local_users_in_room = {
             u
             for u in users_in_room
             if self.hs.is_mine_id(u)
             and not self.get_if_app_services_interested_in_user(u)
-        )
+        }
 
         # users in the room who have pushers need to get push rules run because
         # that's how their pushers work
         if_users_with_pushers = yield self.get_if_users_have_pushers(
             local_users_in_room, on_invalidate=cache_context.invalidate
         )
-        user_ids = set(
+        user_ids = {
             uid for uid, have_pusher in if_users_with_pushers.items() if have_pusher
-        )
+        }
 
         users_with_receipts = yield self.get_users_with_read_receipts_in_room(
             room_id, on_invalidate=cache_context.invalidate
diff --git a/synapse/storage/data_stores/main/receipts.py b/synapse/storage/data_stores/main/receipts.py
index 96e54d145e..0d932a0672 100644
--- a/synapse/storage/data_stores/main/receipts.py
+++ b/synapse/storage/data_stores/main/receipts.py
@@ -58,7 +58,7 @@ class ReceiptsWorkerStore(SQLBaseStore):
     @cachedInlineCallbacks()
     def get_users_with_read_receipts_in_room(self, room_id):
         receipts = yield self.get_receipts_for_room(room_id, "m.read")
-        return set(r["user_id"] for r in receipts)
+        return {r["user_id"] for r in receipts}
 
     @cached(num_args=2)
     def get_receipts_for_room(self, room_id, receipt_type):
@@ -283,7 +283,7 @@ class ReceiptsWorkerStore(SQLBaseStore):
                 args.append(limit)
             txn.execute(sql, args)
 
-            return list(r[0:5] + (json.loads(r[5]),) for r in txn)
+            return [r[0:5] + (json.loads(r[5]),) for r in txn]
 
         return self.db.runInteraction(
             "get_all_updated_receipts", get_all_updated_receipts_txn
diff --git a/synapse/storage/data_stores/main/roommember.py b/synapse/storage/data_stores/main/roommember.py
index d5ced05701..d5bd0cb5cf 100644
--- a/synapse/storage/data_stores/main/roommember.py
+++ b/synapse/storage/data_stores/main/roommember.py
@@ -465,7 +465,7 @@ class RoomMemberWorkerStore(EventsWorkerStore):
 
             txn.execute(sql % (clause,), args)
 
-            return set(row[0] for row in txn)
+            return {row[0] for row in txn}
 
         return await self.db.runInteraction(
             "get_users_server_still_shares_room_with",
@@ -826,7 +826,7 @@ class RoomMemberWorkerStore(EventsWorkerStore):
                 GROUP BY room_id, user_id;
             """
             txn.execute(sql, (user_id,))
-            return set(row[0] for row in txn if row[1] == 0)
+            return {row[0] for row in txn if row[1] == 0}
 
         return self.db.runInteraction(
             "get_forgotten_rooms_for_user", _get_forgotten_rooms_for_user_txn
diff --git a/synapse/storage/data_stores/main/state.py b/synapse/storage/data_stores/main/state.py
index 3d34103e67..3a3b9a8e72 100644
--- a/synapse/storage/data_stores/main/state.py
+++ b/synapse/storage/data_stores/main/state.py
@@ -321,7 +321,7 @@ class StateGroupWorkerStore(EventsWorkerStore, SQLBaseStore):
             desc="get_referenced_state_groups",
         )
 
-        return set(row["state_group"] for row in rows)
+        return {row["state_group"] for row in rows}
 
 
 class MainStateBackgroundUpdateStore(RoomMemberWorkerStore):
@@ -367,7 +367,7 @@ class MainStateBackgroundUpdateStore(RoomMemberWorkerStore):
             """
 
             txn.execute(sql, (last_room_id, batch_size))
-            room_ids = list(row[0] for row in txn)
+            room_ids = [row[0] for row in txn]
             if not room_ids:
                 return True, set()
 
@@ -384,7 +384,7 @@ class MainStateBackgroundUpdateStore(RoomMemberWorkerStore):
 
             txn.execute(sql, (last_room_id, room_ids[-1], "%:" + self.server_name))
 
-            joined_room_ids = set(row[0] for row in txn)
+            joined_room_ids = {row[0] for row in txn}
 
             left_rooms = set(room_ids) - joined_room_ids
 
@@ -404,7 +404,7 @@ class MainStateBackgroundUpdateStore(RoomMemberWorkerStore):
                 retcols=("state_key",),
             )
 
-            potentially_left_users = set(row["state_key"] for row in rows)
+            potentially_left_users = {row["state_key"] for row in rows}
 
             # Now lets actually delete the rooms from the DB.
             self.db.simple_delete_many_txn(
diff --git a/synapse/storage/data_stores/main/stream.py b/synapse/storage/data_stores/main/stream.py
index 056b25b13a..ada5cce6c2 100644
--- a/synapse/storage/data_stores/main/stream.py
+++ b/synapse/storage/data_stores/main/stream.py
@@ -346,11 +346,11 @@ class StreamWorkerStore(EventsWorkerStore, SQLBaseStore):
             from_key (str): The room_key portion of a StreamToken
         """
         from_key = RoomStreamToken.parse_stream_token(from_key).stream
-        return set(
+        return {
             room_id
             for room_id in room_ids
             if self._events_stream_cache.has_entity_changed(room_id, from_key)
-        )
+        }
 
     @defer.inlineCallbacks
     def get_room_events_stream_for_room(
@@ -679,11 +679,11 @@ class StreamWorkerStore(EventsWorkerStore, SQLBaseStore):
         )
 
         events_before = yield self.get_events_as_list(
-            [e for e in results["before"]["event_ids"]], get_prev_content=True
+            list(results["before"]["event_ids"]), get_prev_content=True
         )
 
         events_after = yield self.get_events_as_list(
-            [e for e in results["after"]["event_ids"]], get_prev_content=True
+            list(results["after"]["event_ids"]), get_prev_content=True
         )
 
         return {
diff --git a/synapse/storage/data_stores/main/user_erasure_store.py b/synapse/storage/data_stores/main/user_erasure_store.py
index af8025bc17..ec6b8a4ffd 100644
--- a/synapse/storage/data_stores/main/user_erasure_store.py
+++ b/synapse/storage/data_stores/main/user_erasure_store.py
@@ -63,9 +63,9 @@ class UserErasureWorkerStore(SQLBaseStore):
             retcols=("user_id",),
             desc="are_users_erased",
         )
-        erased_users = set(row["user_id"] for row in rows)
+        erased_users = {row["user_id"] for row in rows}
 
-        res = dict((u, u in erased_users) for u in user_ids)
+        res = {u: u in erased_users for u in user_ids}
         return res
 
 
diff --git a/synapse/storage/data_stores/state/store.py b/synapse/storage/data_stores/state/store.py
index c4ee9b7ccb..57a5267663 100644
--- a/synapse/storage/data_stores/state/store.py
+++ b/synapse/storage/data_stores/state/store.py
@@ -520,11 +520,11 @@ class StateGroupDataStore(StateBackgroundUpdateStore, SQLBaseStore):
             retcols=("state_group",),
         )
 
-        remaining_state_groups = set(
+        remaining_state_groups = {
             row["state_group"]
             for row in rows
             if row["state_group"] not in state_groups_to_delete
-        )
+        }
 
         logger.info(
             "[purge] de-delta-ing %i remaining state groups",
diff --git a/synapse/storage/database.py b/synapse/storage/database.py
index 6dcb5c04da..1953614401 100644
--- a/synapse/storage/database.py
+++ b/synapse/storage/database.py
@@ -554,8 +554,8 @@ class Database(object):
         Returns:
             A list of dicts where the key is the column header.
         """
-        col_headers = list(intern(str(column[0])) for column in cursor.description)
-        results = list(dict(zip(col_headers, row)) for row in cursor)
+        col_headers = [intern(str(column[0])) for column in cursor.description]
+        results = [dict(zip(col_headers, row)) for row in cursor]
         return results
 
     def execute(self, desc, decoder, query, *args):
diff --git a/synapse/storage/persist_events.py b/synapse/storage/persist_events.py
index b950550f23..0f9ac1cf09 100644
--- a/synapse/storage/persist_events.py
+++ b/synapse/storage/persist_events.py
@@ -602,14 +602,14 @@ class EventsPersistenceStorage(object):
             event_id_to_state_group.update(event_to_groups)
 
         # State groups of old_latest_event_ids
-        old_state_groups = set(
+        old_state_groups = {
             event_id_to_state_group[evid] for evid in old_latest_event_ids
-        )
+        }
 
         # State groups of new_latest_event_ids
-        new_state_groups = set(
+        new_state_groups = {
             event_id_to_state_group[evid] for evid in new_latest_event_ids
-        )
+        }
 
         # If they old and new groups are the same then we don't need to do
         # anything.
diff --git a/synapse/storage/prepare_database.py b/synapse/storage/prepare_database.py
index c285ef52a0..fc69c32a0a 100644
--- a/synapse/storage/prepare_database.py
+++ b/synapse/storage/prepare_database.py
@@ -345,9 +345,9 @@ def _upgrade_existing_database(
                     "Could not open delta dir for version %d: %s" % (v, directory)
                 )
 
-        duplicates = set(
+        duplicates = {
             file_name for file_name, count in file_name_counter.items() if count > 1
-        )
+        }
         if duplicates:
             # We don't support using the same file name in the same delta version.
             raise PrepareDatabaseException(
@@ -454,7 +454,7 @@ def _apply_module_schema_files(cur, database_engine, modname, names_and_streams)
         ),
         (modname,),
     )
-    applied_deltas = set(d for d, in cur)
+    applied_deltas = {d for d, in cur}
     for (name, stream) in names_and_streams:
         if name in applied_deltas:
             continue
diff --git a/synapse/util/frozenutils.py b/synapse/util/frozenutils.py
index 635b897d6c..f2ccd5e7c6 100644
--- a/synapse/util/frozenutils.py
+++ b/synapse/util/frozenutils.py
@@ -30,7 +30,7 @@ def freeze(o):
         return o
 
     try:
-        return tuple([freeze(i) for i in o])
+        return tuple(freeze(i) for i in o)
     except TypeError:
         pass
 
diff --git a/synapse/visibility.py b/synapse/visibility.py
index d0abd8f04f..e60d9756b7 100644
--- a/synapse/visibility.py
+++ b/synapse/visibility.py
@@ -75,7 +75,7 @@ def filter_events_for_client(
     """
     # Filter out events that have been soft failed so that we don't relay them
     # to clients.
-    events = list(e for e in events if not e.internal_metadata.is_soft_failed())
+    events = [e for e in events if not e.internal_metadata.is_soft_failed()]
 
     types = ((EventTypes.RoomHistoryVisibility, ""), (EventTypes.Member, user_id))
     event_id_to_state = yield storage.state.get_state_for_events(
@@ -97,7 +97,7 @@ def filter_events_for_client(
     erased_senders = yield storage.main.are_users_erased((e.sender for e in events))
 
     if apply_retention_policies:
-        room_ids = set(e.room_id for e in events)
+        room_ids = {e.room_id for e in events}
         retention_policies = {}
 
         for room_id in room_ids: