Use inline type hints in `handlers/` and `rest/`. (#10382)

43 files changed, 212 insertions, 215 deletions

diff --git a/changelog.d/10382.misc b/changelog.d/10382.misc
new file mode 100644
index 0000000000..eed2d8552a
--- /dev/null
+++ b/changelog.d/10382.misc
@@ -0,0 +1 @@
+Convert internal type variable syntax to reflect wider ecosystem use.
\ No newline at end of file
diff --git a/synapse/handlers/_base.py b/synapse/handlers/_base.py
index d800e16912..525f3d39b1 100644
--- a/synapse/handlers/_base.py
+++ b/synapse/handlers/_base.py
@@ -38,10 +38,10 @@ class BaseHandler:
     """
 
     def __init__(self, hs: "HomeServer"):
-        self.store = hs.get_datastore()  # type: synapse.storage.DataStore
+        self.store = hs.get_datastore()
         self.auth = hs.get_auth()
         self.notifier = hs.get_notifier()
-        self.state_handler = hs.get_state_handler()  # type: synapse.state.StateHandler
+        self.state_handler = hs.get_state_handler()
         self.distributor = hs.get_distributor()
         self.clock = hs.get_clock()
         self.hs = hs
@@ -55,12 +55,12 @@ class BaseHandler:
         # Check whether ratelimiting room admin message redaction is enabled
         # by the presence of rate limits in the config
         if self.hs.config.rc_admin_redaction:
-            self.admin_redaction_ratelimiter = Ratelimiter(
+            self.admin_redaction_ratelimiter: Optional[Ratelimiter] = Ratelimiter(
                 store=self.store,
                 clock=self.clock,
                 rate_hz=self.hs.config.rc_admin_redaction.per_second,
                 burst_count=self.hs.config.rc_admin_redaction.burst_count,
-            )  # type: Optional[Ratelimiter]
+            )
         else:
             self.admin_redaction_ratelimiter = None
 
diff --git a/synapse/handlers/admin.py b/synapse/handlers/admin.py
index d75a8b15c3..bfa7f2c545 100644
--- a/synapse/handlers/admin.py
+++ b/synapse/handlers/admin.py
@@ -139,7 +139,7 @@ class AdminHandler(BaseHandler):
             to_key = RoomStreamToken(None, stream_ordering)
 
             # Events that we've processed in this room
-            written_events = set()  # type: Set[str]
+            written_events: Set[str] = set()
 
             # We need to track gaps in the events stream so that we can then
             # write out the state at those events. We do this by keeping track
@@ -152,7 +152,7 @@ class AdminHandler(BaseHandler):
             # The reverse mapping to above, i.e. map from unseen event to events
             # that have the unseen event in their prev_events, i.e. the unseen
             # events "children".
-            unseen_to_child_events = {}  # type: Dict[str, Set[str]]
+            unseen_to_child_events: Dict[str, Set[str]] = {}
 
             # We fetch events in the room the user could see by fetching *all*
             # events that we have and then filtering, this isn't the most
diff --git a/synapse/handlers/appservice.py b/synapse/handlers/appservice.py
index 862638cc4f..21a17cd2e8 100644
--- a/synapse/handlers/appservice.py
+++ b/synapse/handlers/appservice.py
@@ -96,7 +96,7 @@ class ApplicationServicesHandler:
                         self.current_max, limit
                     )
 
-                    events_by_room = {}  # type: Dict[str, List[EventBase]]
+                    events_by_room: Dict[str, List[EventBase]] = {}
                     for event in events:
                         events_by_room.setdefault(event.room_id, []).append(event)
 
@@ -275,7 +275,7 @@ class ApplicationServicesHandler:
     async def _handle_presence(
         self, service: ApplicationService, users: Collection[Union[str, UserID]]
     ) -> List[JsonDict]:
-        events = []  # type: List[JsonDict]
+        events: List[JsonDict] = []
         presence_source = self.event_sources.sources["presence"]
         from_key = await self.store.get_type_stream_id_for_appservice(
             service, "presence"
@@ -375,7 +375,7 @@ class ApplicationServicesHandler:
         self, only_protocol: Optional[str] = None
     ) -> Dict[str, JsonDict]:
         services = self.store.get_app_services()
-        protocols = {}  # type: Dict[str, List[JsonDict]]
+        protocols: Dict[str, List[JsonDict]] = {}
 
         # Collect up all the individual protocol responses out of the ASes
         for s in services:
diff --git a/synapse/handlers/auth.py b/synapse/handlers/auth.py
index e2ac595a62..22a8552241 100644
--- a/synapse/handlers/auth.py
+++ b/synapse/handlers/auth.py
@@ -191,7 +191,7 @@ class AuthHandler(BaseHandler):
     def __init__(self, hs: "HomeServer"):
         super().__init__(hs)
 
-        self.checkers = {}  # type: Dict[str, UserInteractiveAuthChecker]
+        self.checkers: Dict[str, UserInteractiveAuthChecker] = {}
         for auth_checker_class in INTERACTIVE_AUTH_CHECKERS:
             inst = auth_checker_class(hs)
             if inst.is_enabled():
@@ -296,7 +296,7 @@ class AuthHandler(BaseHandler):
 
         # A mapping of user ID to extra attributes to include in the login
         # response.
-        self._extra_attributes = {}  # type: Dict[str, SsoLoginExtraAttributes]
+        self._extra_attributes: Dict[str, SsoLoginExtraAttributes] = {}
 
     async def validate_user_via_ui_auth(
         self,
@@ -500,7 +500,7 @@ class AuthHandler(BaseHandler):
                 all the stages in any of the permitted flows.
         """
 
-        sid = None  # type: Optional[str]
+        sid: Optional[str] = None
         authdict = clientdict.pop("auth", {})
         if "session" in authdict:
             sid = authdict["session"]
@@ -588,9 +588,9 @@ class AuthHandler(BaseHandler):
             )
 
         # check auth type currently being presented
-        errordict = {}  # type: Dict[str, Any]
+        errordict: Dict[str, Any] = {}
         if "type" in authdict:
-            login_type = authdict["type"]  # type: str
+            login_type: str = authdict["type"]
             try:
                 result = await self._check_auth_dict(authdict, clientip)
                 if result:
@@ -766,7 +766,7 @@ class AuthHandler(BaseHandler):
             LoginType.TERMS: self._get_params_terms,
         }
 
-        params = {}  # type: Dict[str, Any]
+        params: Dict[str, Any] = {}
 
         for f in public_flows:
             for stage in f:
@@ -1530,9 +1530,9 @@ class AuthHandler(BaseHandler):
         except StoreError:
             raise SynapseError(400, "Unknown session ID: %s" % (session_id,))
 
-        user_id_to_verify = await self.get_session_data(
+        user_id_to_verify: str = await self.get_session_data(
             session_id, UIAuthSessionDataConstants.REQUEST_USER_ID
-        )  # type: str
+        )
 
         idps = await self.hs.get_sso_handler().get_identity_providers_for_user(
             user_id_to_verify
diff --git a/synapse/handlers/cas.py b/synapse/handlers/cas.py
index 7346ccfe93..b681d208bc 100644
--- a/synapse/handlers/cas.py
+++ b/synapse/handlers/cas.py
@@ -171,7 +171,7 @@ class CasHandler:
 
         # Iterate through the nodes and pull out the user and any extra attributes.
         user = None
-        attributes = {}  # type: Dict[str, List[Optional[str]]]
+        attributes: Dict[str, List[Optional[str]]] = {}
         for child in root[0]:
             if child.tag.endswith("user"):
                 user = child.text
diff --git a/synapse/handlers/device.py b/synapse/handlers/device.py
index 95bdc5902a..46ee834407 100644
--- a/synapse/handlers/device.py
+++ b/synapse/handlers/device.py
@@ -452,7 +452,7 @@ class DeviceHandler(DeviceWorkerHandler):
             user_id
         )
 
-        hosts = set()  # type: Set[str]
+        hosts: Set[str] = set()
         if self.hs.is_mine_id(user_id):
             hosts.update(get_domain_from_id(u) for u in users_who_share_room)
             hosts.discard(self.server_name)
@@ -613,20 +613,20 @@ class DeviceListUpdater:
         self._remote_edu_linearizer = Linearizer(name="remote_device_list")
 
         # user_id -> list of updates waiting to be handled.
-        self._pending_updates = (
-            {}
-        )  # type: Dict[str, List[Tuple[str, str, Iterable[str], JsonDict]]]
+        self._pending_updates: Dict[
+            str, List[Tuple[str, str, Iterable[str], JsonDict]]
+        ] = {}
 
         # Recently seen stream ids. We don't bother keeping these in the DB,
         # but they're useful to have them about to reduce the number of spurious
         # resyncs.
-        self._seen_updates = ExpiringCache(
+        self._seen_updates: ExpiringCache[str, Set[str]] = ExpiringCache(
             cache_name="device_update_edu",
             clock=self.clock,
             max_len=10000,
             expiry_ms=30 * 60 * 1000,
             iterable=True,
-        )  # type: ExpiringCache[str, Set[str]]
+        )
 
         # Attempt to resync out of sync device lists every 30s.
         self._resync_retry_in_progress = False
@@ -755,7 +755,7 @@ class DeviceListUpdater:
         """Given a list of updates for a user figure out if we need to do a full
         resync, or whether we have enough data that we can just apply the delta.
         """
-        seen_updates = self._seen_updates.get(user_id, set())  # type: Set[str]
+        seen_updates: Set[str] = self._seen_updates.get(user_id, set())
 
         extremity = await self.store.get_device_list_last_stream_id_for_remote(user_id)
 
diff --git a/synapse/handlers/devicemessage.py b/synapse/handlers/devicemessage.py
index 580b941595..679b47f081 100644
--- a/synapse/handlers/devicemessage.py
+++ b/synapse/handlers/devicemessage.py
@@ -203,7 +203,7 @@ class DeviceMessageHandler:
         log_kv({"number_of_to_device_messages": len(messages)})
         set_tag("sender", sender_user_id)
         local_messages = {}
-        remote_messages = {}  # type: Dict[str, Dict[str, Dict[str, JsonDict]]]
+        remote_messages: Dict[str, Dict[str, Dict[str, JsonDict]]] = {}
         for user_id, by_device in messages.items():
             # Ratelimit local cross-user key requests by the sending device.
             if (
diff --git a/synapse/handlers/directory.py b/synapse/handlers/directory.py
index 06d7012bac..d487fee627 100644
--- a/synapse/handlers/directory.py
+++ b/synapse/handlers/directory.py
@@ -237,9 +237,9 @@ class DirectoryHandler(BaseHandler):
     async def get_association(self, room_alias: RoomAlias) -> JsonDict:
         room_id = None
         if self.hs.is_mine(room_alias):
-            result = await self.get_association_from_room_alias(
-                room_alias
-            )  # type: Optional[RoomAliasMapping]
+            result: Optional[
+                RoomAliasMapping
+            ] = await self.get_association_from_room_alias(room_alias)
 
             if result:
                 room_id = result.room_id
diff --git a/synapse/handlers/e2e_keys.py b/synapse/handlers/e2e_keys.py
index 3972849d4d..d92370859f 100644
--- a/synapse/handlers/e2e_keys.py
+++ b/synapse/handlers/e2e_keys.py
@@ -115,9 +115,9 @@ class E2eKeysHandler:
                 the number of in-flight queries at a time.
         """
         with await self._query_devices_linearizer.queue((from_user_id, from_device_id)):
-            device_keys_query = query_body.get(
+            device_keys_query: Dict[str, Iterable[str]] = query_body.get(
                 "device_keys", {}
-            )  # type: Dict[str, Iterable[str]]
+            )
 
             # separate users by domain.
             # make a map from domain to user_id to device_ids
@@ -136,7 +136,7 @@ class E2eKeysHandler:
 
             # First get local devices.
             # A map of destination -> failure response.
-            failures = {}  # type: Dict[str, JsonDict]
+            failures: Dict[str, JsonDict] = {}
             results = {}
             if local_query:
                 local_result = await self.query_local_devices(local_query)
@@ -151,11 +151,9 @@ class E2eKeysHandler:
 
             # Now attempt to get any remote devices from our local cache.
             # A map of destination -> user ID -> device IDs.
-            remote_queries_not_in_cache = (
-                {}
-            )  # type: Dict[str, Dict[str, Iterable[str]]]
+            remote_queries_not_in_cache: Dict[str, Dict[str, Iterable[str]]] = {}
             if remote_queries:
-                query_list = []  # type: List[Tuple[str, Optional[str]]]
+                query_list: List[Tuple[str, Optional[str]]] = []
                 for user_id, device_ids in remote_queries.items():
                     if device_ids:
                         query_list.extend(
@@ -362,9 +360,9 @@ class E2eKeysHandler:
             A map from user_id -> device_id -> device details
         """
         set_tag("local_query", query)
-        local_query = []  # type: List[Tuple[str, Optional[str]]]
+        local_query: List[Tuple[str, Optional[str]]] = []
 
-        result_dict = {}  # type: Dict[str, Dict[str, dict]]
+        result_dict: Dict[str, Dict[str, dict]] = {}
         for user_id, device_ids in query.items():
             # we use UserID.from_string to catch invalid user ids
             if not self.is_mine(UserID.from_string(user_id)):
@@ -402,9 +400,9 @@ class E2eKeysHandler:
         self, query_body: Dict[str, Dict[str, Optional[List[str]]]]
     ) -> JsonDict:
         """Handle a device key query from a federated server"""
-        device_keys_query = query_body.get(
+        device_keys_query: Dict[str, Optional[List[str]]] = query_body.get(
             "device_keys", {}
-        )  # type: Dict[str, Optional[List[str]]]
+        )
         res = await self.query_local_devices(device_keys_query)
         ret = {"device_keys": res}
 
@@ -421,8 +419,8 @@ class E2eKeysHandler:
     async def claim_one_time_keys(
         self, query: Dict[str, Dict[str, Dict[str, str]]], timeout: int
     ) -> JsonDict:
-        local_query = []  # type: List[Tuple[str, str, str]]
-        remote_queries = {}  # type: Dict[str, Dict[str, Dict[str, str]]]
+        local_query: List[Tuple[str, str, str]] = []
+        remote_queries: Dict[str, Dict[str, Dict[str, str]]] = {}
 
         for user_id, one_time_keys in query.get("one_time_keys", {}).items():
             # we use UserID.from_string to catch invalid user ids
@@ -439,8 +437,8 @@ class E2eKeysHandler:
         results = await self.store.claim_e2e_one_time_keys(local_query)
 
         # A map of user ID -> device ID -> key ID -> key.
-        json_result = {}  # type: Dict[str, Dict[str, Dict[str, JsonDict]]]
-        failures = {}  # type: Dict[str, JsonDict]
+        json_result: Dict[str, Dict[str, Dict[str, JsonDict]]] = {}
+        failures: Dict[str, JsonDict] = {}
         for user_id, device_keys in results.items():
             for device_id, keys in device_keys.items():
                 for key_id, json_str in keys.items():
@@ -768,8 +766,8 @@ class E2eKeysHandler:
         Raises:
             SynapseError: if the input is malformed
         """
-        signature_list = []  # type: List[SignatureListItem]
-        failures = {}  # type: Dict[str, Dict[str, JsonDict]]
+        signature_list: List["SignatureListItem"] = []
+        failures: Dict[str, Dict[str, JsonDict]] = {}
         if not signatures:
             return signature_list, failures
 
@@ -930,8 +928,8 @@ class E2eKeysHandler:
         Raises:
             SynapseError: if the input is malformed
         """
-        signature_list = []  # type: List[SignatureListItem]
-        failures = {}  # type: Dict[str, Dict[str, JsonDict]]
+        signature_list: List["SignatureListItem"] = []
+        failures: Dict[str, Dict[str, JsonDict]] = {}
         if not signatures:
             return signature_list, failures
 
@@ -1300,7 +1298,7 @@ class SigningKeyEduUpdater:
         self._remote_edu_linearizer = Linearizer(name="remote_signing_key")
 
         # user_id -> list of updates waiting to be handled.
-        self._pending_updates = {}  # type: Dict[str, List[Tuple[JsonDict, JsonDict]]]
+        self._pending_updates: Dict[str, List[Tuple[JsonDict, JsonDict]]] = {}
 
     async def incoming_signing_key_update(
         self, origin: str, edu_content: JsonDict
@@ -1349,7 +1347,7 @@ class SigningKeyEduUpdater:
                 # This can happen since we batch updates
                 return
 
-            device_ids = []  # type: List[str]
+            device_ids: List[str] = []
 
             logger.info("pending updates: %r", pending_updates)
 
diff --git a/synapse/handlers/events.py b/synapse/handlers/events.py
index f134f1e234..4b3f037072 100644
--- a/synapse/handlers/events.py
+++ b/synapse/handlers/events.py
@@ -93,7 +93,7 @@ class EventStreamHandler(BaseHandler):
 
             # When the user joins a new room, or another user joins a currently
             # joined room, we need to send down presence for those users.
-            to_add = []  # type: List[JsonDict]
+            to_add: List[JsonDict] = []
             for event in events:
                 if not isinstance(event, EventBase):
                     continue
@@ -103,9 +103,9 @@ class EventStreamHandler(BaseHandler):
                     # Send down presence.
                     if event.state_key == auth_user_id:
                         # Send down presence for everyone in the room.
-                        users = await self.store.get_users_in_room(
+                        users: Iterable[str] = await self.store.get_users_in_room(
                             event.room_id
-                        )  # type: Iterable[str]
+                        )
                     else:
                         users = [event.state_key]
 
diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index 0209aee186..5c4463583e 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -181,7 +181,7 @@ class FederationHandler(BaseHandler):
 
         # When joining a room we need to queue any events for that room up.
         # For each room, a list of (pdu, origin) tuples.
-        self.room_queues = {}  # type: Dict[str, List[Tuple[EventBase, str]]]
+        self.room_queues: Dict[str, List[Tuple[EventBase, str]]] = {}
         self._room_pdu_linearizer = Linearizer("fed_room_pdu")
 
         self._room_backfill = Linearizer("room_backfill")
@@ -368,7 +368,7 @@ class FederationHandler(BaseHandler):
                     ours = await self.state_store.get_state_groups_ids(room_id, seen)
 
                     # state_maps is a list of mappings from (type, state_key) to event_id
-                    state_maps = list(ours.values())  # type: List[StateMap[str]]
+                    state_maps: List[StateMap[str]] = list(ours.values())
 
                     # we don't need this any more, let's delete it.
                     del ours
@@ -845,7 +845,7 @@ class FederationHandler(BaseHandler):
                 # exact key to expect. Otherwise check it matches any key we
                 # have for that device.
 
-                current_keys = []  # type: Container[str]
+                current_keys: Container[str] = []
 
                 if device:
                     keys = device.get("keys", {}).get("keys", {})
@@ -1185,7 +1185,7 @@ class FederationHandler(BaseHandler):
                 if e_type == EventTypes.Member and event.membership == Membership.JOIN
             ]
 
-            joined_domains = {}  # type: Dict[str, int]
+            joined_domains: Dict[str, int] = {}
             for u, d in joined_users:
                 try:
                     dom = get_domain_from_id(u)
@@ -1314,7 +1314,7 @@ class FederationHandler(BaseHandler):
 
         room_version = await self.store.get_room_version(room_id)
 
-        event_map = {}  # type: Dict[str, EventBase]
+        event_map: Dict[str, EventBase] = {}
 
         async def get_event(event_id: str):
             with nested_logging_context(event_id):
@@ -1596,7 +1596,7 @@ class FederationHandler(BaseHandler):
 
         # Ask the remote server to create a valid knock event for us. Once received,
         # we sign the event
-        params = {"ver": supported_room_versions}  # type: Dict[str, Iterable[str]]
+        params: Dict[str, Iterable[str]] = {"ver": supported_room_versions}
         origin, event, event_format_version = await self._make_and_verify_event(
             target_hosts, room_id, knockee, Membership.KNOCK, content, params=params
         )
@@ -2453,14 +2453,14 @@ class FederationHandler(BaseHandler):
             state_sets_d = await self.state_store.get_state_groups(
                 event.room_id, extrem_ids
             )
-            state_sets = list(state_sets_d.values())  # type: List[Iterable[EventBase]]
+            state_sets: List[Iterable[EventBase]] = list(state_sets_d.values())
             state_sets.append(state)
             current_states = await self.state_handler.resolve_events(
                 room_version, state_sets, event
             )
-            current_state_ids = {
+            current_state_ids: StateMap[str] = {
                 k: e.event_id for k, e in current_states.items()
-            }  # type: StateMap[str]
+            }
         else:
             current_state_ids = await self.state_handler.get_current_state_ids(
                 event.room_id, latest_event_ids=extrem_ids
@@ -2817,7 +2817,7 @@ class FederationHandler(BaseHandler):
         """
         # exclude the state key of the new event from the current_state in the context.
         if event.is_state():
-            event_key = (event.type, event.state_key)  # type: Optional[Tuple[str, str]]
+            event_key: Optional[Tuple[str, str]] = (event.type, event.state_key)
         else:
             event_key = None
         state_updates = {
@@ -3156,7 +3156,7 @@ class FederationHandler(BaseHandler):
 
         logger.debug("Checking auth on event %r", event.content)
 
-        last_exception = None  # type: Optional[Exception]
+        last_exception: Optional[Exception] = None
 
         # for each public key in the 3pid invite event
         for public_key_object in event_auth.get_public_keys(invite_event):
diff --git a/synapse/handlers/groups_local.py b/synapse/handlers/groups_local.py
index 157f2ff218..1a6c5c64a2 100644
--- a/synapse/handlers/groups_local.py
+++ b/synapse/handlers/groups_local.py
@@ -214,7 +214,7 @@ class GroupsLocalWorkerHandler:
     async def bulk_get_publicised_groups(
         self, user_ids: Iterable[str], proxy: bool = True
     ) -> JsonDict:
-        destinations = {}  # type: Dict[str, Set[str]]
+        destinations: Dict[str, Set[str]] = {}
         local_users = set()
 
         for user_id in user_ids:
@@ -227,7 +227,7 @@ class GroupsLocalWorkerHandler:
             raise SynapseError(400, "Some user_ids are not local")
 
         results = {}
-        failed_results = []  # type: List[str]
+        failed_results: List[str] = []
         for destination, dest_user_ids in destinations.items():
             try:
                 r = await self.transport_client.bulk_get_publicised_groups(
diff --git a/synapse/handlers/initial_sync.py b/synapse/handlers/initial_sync.py
index 76242865ae..5d49640760 100644
--- a/synapse/handlers/initial_sync.py
+++ b/synapse/handlers/initial_sync.py
@@ -46,9 +46,17 @@ class InitialSyncHandler(BaseHandler):
         self.state = hs.get_state_handler()
         self.clock = hs.get_clock()
         self.validator = EventValidator()
-        self.snapshot_cache = ResponseCache(
-            hs.get_clock(), "initial_sync_cache"
-        )  # type: ResponseCache[Tuple[str, Optional[StreamToken], Optional[StreamToken], str, Optional[int], bool, bool]]
+        self.snapshot_cache: ResponseCache[
+            Tuple[
+                str,
+                Optional[StreamToken],
+                Optional[StreamToken],
+                str,
+                Optional[int],
+                bool,
+                bool,
+            ]
+        ] = ResponseCache(hs.get_clock(), "initial_sync_cache")
         self._event_serializer = hs.get_event_client_serializer()
         self.storage = hs.get_storage()
         self.state_store = self.storage.state
diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py
index e06655f3d4..c7fe4ff89e 100644
--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -81,7 +81,7 @@ class MessageHandler:
 
         # The scheduled call to self._expire_event. None if no call is currently
         # scheduled.
-        self._scheduled_expiry = None  # type: Optional[IDelayedCall]
+        self._scheduled_expiry: Optional[IDelayedCall] = None
 
         if not hs.config.worker_app:
             run_as_background_process(
@@ -196,9 +196,7 @@ class MessageHandler:
                 room_state_events = await self.state_store.get_state_for_events(
                     [event.event_id], state_filter=state_filter
                 )
-                room_state = room_state_events[
-                    event.event_id
-                ]  # type: Mapping[Any, EventBase]
+                room_state: Mapping[Any, EventBase] = room_state_events[event.event_id]
             else:
                 raise AuthError(
                     403,
@@ -421,9 +419,9 @@ class EventCreationHandler:
         self.action_generator = hs.get_action_generator()
 
         self.spam_checker = hs.get_spam_checker()
-        self.third_party_event_rules = (
+        self.third_party_event_rules: "ThirdPartyEventRules" = (
             self.hs.get_third_party_event_rules()
-        )  # type: ThirdPartyEventRules
+        )
 
         self._block_events_without_consent_error = (
             self.config.block_events_without_consent_error
@@ -440,7 +438,7 @@ class EventCreationHandler:
         #
         # map from room id to time-of-last-attempt.
         #
-        self._rooms_to_exclude_from_dummy_event_insertion = {}  # type: Dict[str, int]
+        self._rooms_to_exclude_from_dummy_event_insertion: Dict[str, int] = {}
         # The number of forward extremeities before a dummy event is sent.
         self._dummy_events_threshold = hs.config.dummy_events_threshold
 
@@ -465,9 +463,7 @@ class EventCreationHandler:
         # Stores the state groups we've recently added to the joined hosts
         # external cache. Note that the timeout must be significantly less than
         # the TTL on the external cache.
-        self._external_cache_joined_hosts_updates = (
-            None
-        )  # type: Optional[ExpiringCache]
+        self._external_cache_joined_hosts_updates: Optional[ExpiringCache] = None
         if self._external_cache.is_enabled():
             self._external_cache_joined_hosts_updates = ExpiringCache(
                 "_external_cache_joined_hosts_updates",
@@ -1299,7 +1295,7 @@ class EventCreationHandler:
             # Validate a newly added alias or newly added alt_aliases.
 
             original_alias = None
-            original_alt_aliases = []  # type: List[str]
+            original_alt_aliases: List[str] = []
 
             original_event_id = event.unsigned.get("replaces_state")
             if original_event_id:
diff --git a/synapse/handlers/oidc.py b/synapse/handlers/oidc.py
index ee6e41c0e4..a330c48fa7 100644
--- a/synapse/handlers/oidc.py
+++ b/synapse/handlers/oidc.py
@@ -105,9 +105,9 @@ class OidcHandler:
         assert provider_confs
 
         self._token_generator = OidcSessionTokenGenerator(hs)
-        self._providers = {
+        self._providers: Dict[str, "OidcProvider"] = {
             p.idp_id: OidcProvider(hs, self._token_generator, p) for p in provider_confs
-        }  # type: Dict[str, OidcProvider]
+        }
 
     async def load_metadata(self) -> None:
         """Validate the config and load the metadata from the remote endpoint.
@@ -178,7 +178,7 @@ class OidcHandler:
         # are two.
 
         for cookie_name, _ in _SESSION_COOKIES:
-            session = request.getCookie(cookie_name)  # type: Optional[bytes]
+            session: Optional[bytes] = request.getCookie(cookie_name)
             if session is not None:
                 break
         else:
@@ -277,7 +277,7 @@ class OidcProvider:
         self._token_generator = token_generator
 
         self._config = provider
-        self._callback_url = hs.config.oidc_callback_url  # type: str
+        self._callback_url: str = hs.config.oidc_callback_url
 
         # Calculate the prefix for OIDC callback paths based on the public_baseurl.
         # We'll insert this into the Path= parameter of any session cookies we set.
@@ -290,7 +290,7 @@ class OidcProvider:
         self._scopes = provider.scopes
         self._user_profile_method = provider.user_profile_method
 
-        client_secret = None  # type: Union[None, str, JwtClientSecret]
+        client_secret: Optional[Union[str, JwtClientSecret]] = None
         if provider.client_secret:
             client_secret = provider.client_secret
         elif provider.client_secret_jwt_key:
@@ -305,7 +305,7 @@ class OidcProvider:
             provider.client_id,
             client_secret,
             provider.client_auth_method,
-        )  # type: ClientAuth
+        )
         self._client_auth_method = provider.client_auth_method
 
         # cache of metadata for the identity provider (endpoint uris, mostly). This is
@@ -324,7 +324,7 @@ class OidcProvider:
         self._allow_existing_users = provider.allow_existing_users
 
         self._http_client = hs.get_proxied_http_client()
-        self._server_name = hs.config.server_name  # type: str
+        self._server_name: str = hs.config.server_name
 
         # identifier for the external_ids table
         self.idp_id = provider.idp_id
@@ -1381,7 +1381,7 @@ class JinjaOidcMappingProvider(OidcMappingProvider[JinjaOidcMappingConfig]):
         if display_name == "":
             display_name = None
 
-        emails = []  # type: List[str]
+        emails: List[str] = []
         email = render_template_field(self._config.email_template)
         if email:
             emails.append(email)
@@ -1391,7 +1391,7 @@ class JinjaOidcMappingProvider(OidcMappingProvider[JinjaOidcMappingConfig]):
         )
 
     async def get_extra_attributes(self, userinfo: UserInfo, token: Token) -> JsonDict:
-        extras = {}  # type: Dict[str, str]
+        extras: Dict[str, str] = {}
         for key, template in self._config.extra_attributes.items():
             try:
                 extras[key] = template.render(user=userinfo).strip()
diff --git a/synapse/handlers/pagination.py b/synapse/handlers/pagination.py
index 1e1186c29e..1dbafd253d 100644
--- a/synapse/handlers/pagination.py
+++ b/synapse/handlers/pagination.py
@@ -81,9 +81,9 @@ class PaginationHandler:
         self._server_name = hs.hostname
 
         self.pagination_lock = ReadWriteLock()
-        self._purges_in_progress_by_room = set()  # type: Set[str]
+        self._purges_in_progress_by_room: Set[str] = set()
         # map from purge id to PurgeStatus
-        self._purges_by_id = {}  # type: Dict[str, PurgeStatus]
+        self._purges_by_id: Dict[str, PurgeStatus] = {}
         self._event_serializer = hs.get_event_client_serializer()
 
         self._retention_default_max_lifetime = hs.config.retention_default_max_lifetime
diff --git a/synapse/handlers/presence.py b/synapse/handlers/presence.py
index 44ed7a0712..016c5df2ca 100644
--- a/synapse/handlers/presence.py
+++ b/synapse/handlers/presence.py
@@ -378,14 +378,14 @@ class WorkerPresenceHandler(BasePresenceHandler):
 
         # The number of ongoing syncs on this process, by user id.
         # Empty if _presence_enabled is false.
-        self._user_to_num_current_syncs = {}  # type: Dict[str, int]
+        self._user_to_num_current_syncs: Dict[str, int] = {}
 
         self.notifier = hs.get_notifier()
         self.instance_id = hs.get_instance_id()
 
         # user_id -> last_sync_ms. Lists the users that have stopped syncing but
         # we haven't notified the presence writer of that yet
-        self.users_going_offline = {}  # type: Dict[str, int]
+        self.users_going_offline: Dict[str, int] = {}
 
         self._bump_active_client = ReplicationBumpPresenceActiveTime.make_client(hs)
         self._set_state_client = ReplicationPresenceSetState.make_client(hs)
@@ -650,7 +650,7 @@ class PresenceHandler(BasePresenceHandler):
 
         # Set of users who have presence in the `user_to_current_state` that
         # have not yet been persisted
-        self.unpersisted_users_changes = set()  # type: Set[str]
+        self.unpersisted_users_changes: Set[str] = set()
 
         hs.get_reactor().addSystemEventTrigger(
             "before",
@@ -664,7 +664,7 @@ class PresenceHandler(BasePresenceHandler):
 
         # Keeps track of the number of *ongoing* syncs on this process. While
         # this is non zero a user will never go offline.
-        self.user_to_num_current_syncs = {}  # type: Dict[str, int]
+        self.user_to_num_current_syncs: Dict[str, int] = {}
 
         # Keeps track of the number of *ongoing* syncs on other processes.
         # While any sync is ongoing on another process the user will never
@@ -674,8 +674,8 @@ class PresenceHandler(BasePresenceHandler):
         # we assume that all the sync requests on that process have stopped.
         # Stored as a dict from process_id to set of user_id, and a dict of
         # process_id to millisecond timestamp last updated.
-        self.external_process_to_current_syncs = {}  # type: Dict[str, Set[str]]
-        self.external_process_last_updated_ms = {}  # type: Dict[str, int]
+        self.external_process_to_current_syncs: Dict[str, Set[str]] = {}
+        self.external_process_last_updated_ms: Dict[str, int] = {}
 
         self.external_sync_linearizer = Linearizer(name="external_sync_linearizer")
 
@@ -1581,9 +1581,7 @@ class PresenceEventSource:
 
             # The set of users that we're interested in and that have had a presence update.
             # We'll actually pull the presence updates for these users at the end.
-            interested_and_updated_users = (
-                set()
-            )  # type: Union[Set[str], FrozenSet[str]]
+            interested_and_updated_users: Union[Set[str], FrozenSet[str]] = set()
 
             if from_key:
                 # First get all users that have had a presence update
@@ -1950,8 +1948,8 @@ async def get_interested_parties(
         A 2-tuple of `(room_ids_to_states, users_to_states)`,
         with each item being a dict of `entity_name` -> `[UserPresenceState]`
     """
-    room_ids_to_states = {}  # type: Dict[str, List[UserPresenceState]]
-    users_to_states = {}  # type: Dict[str, List[UserPresenceState]]
+    room_ids_to_states: Dict[str, List[UserPresenceState]] = {}
+    users_to_states: Dict[str, List[UserPresenceState]] = {}
     for state in states:
         room_ids = await store.get_rooms_for_user(state.user_id)
         for room_id in room_ids:
@@ -2063,12 +2061,12 @@ class PresenceFederationQueue:
         # stream_id, destinations, user_ids)`. We don't store the full states
         # for efficiency, and remote workers will already have the full states
         # cached.
-        self._queue = []  # type: List[Tuple[int, int, Collection[str], Set[str]]]
+        self._queue: List[Tuple[int, int, Collection[str], Set[str]]] = []
 
         self._next_id = 1
 
         # Map from instance name to current token
-        self._current_tokens = {}  # type: Dict[str, int]
+        self._current_tokens: Dict[str, int] = {}
 
         if self._queue_presence_updates:
             self._clock.looping_call(self._clear_queue, self._CLEAR_ITEMS_EVERY_MS)
@@ -2168,7 +2166,7 @@ class PresenceFederationQueue:
         # handle the case where `from_token` stream ID has already been dropped.
         start_idx = max(from_token + 1 - self._next_id, -len(self._queue))
 
-        to_send = []  # type: List[Tuple[int, Tuple[str, str]]]
+        to_send: List[Tuple[int, Tuple[str, str]]] = []
         limited = False
         new_id = upto_token
         for _, stream_id, destinations, user_ids in self._queue[start_idx:]:
@@ -2216,7 +2214,7 @@ class PresenceFederationQueue:
         if not self._federation:
             return
 
-        hosts_to_users = {}  # type: Dict[str, Set[str]]
+        hosts_to_users: Dict[str, Set[str]] = {}
         for row in rows:
             hosts_to_users.setdefault(row.destination, set()).add(row.user_id)
 
diff --git a/synapse/handlers/profile.py b/synapse/handlers/profile.py
index 05b4a97b59..20a033d0ba 100644
--- a/synapse/handlers/profile.py
+++ b/synapse/handlers/profile.py
@@ -197,7 +197,7 @@ class ProfileHandler(BaseHandler):
                 400, "Displayname is too long (max %i)" % (MAX_DISPLAYNAME_LEN,)
             )
 
-        displayname_to_set = new_displayname  # type: Optional[str]
+        displayname_to_set: Optional[str] = new_displayname
         if new_displayname == "":
             displayname_to_set = None
 
@@ -286,7 +286,7 @@ class ProfileHandler(BaseHandler):
                 400, "Avatar URL is too long (max %i)" % (MAX_AVATAR_URL_LEN,)
             )
 
-        avatar_url_to_set = new_avatar_url  # type: Optional[str]
+        avatar_url_to_set: Optional[str] = new_avatar_url
         if new_avatar_url == "":
             avatar_url_to_set = None
 
diff --git a/synapse/handlers/receipts.py b/synapse/handlers/receipts.py
index 0059ad0f56..283483fc2c 100644
--- a/synapse/handlers/receipts.py
+++ b/synapse/handlers/receipts.py
@@ -98,8 +98,8 @@ class ReceiptsHandler(BaseHandler):
 
     async def _handle_new_receipts(self, receipts: List[ReadReceipt]) -> bool:
         """Takes a list of receipts, stores them and informs the notifier."""
-        min_batch_id = None  # type: Optional[int]
-        max_batch_id = None  # type: Optional[int]
+        min_batch_id: Optional[int] = None
+        max_batch_id: Optional[int] = None
 
         for receipt in receipts:
             res = await self.store.insert_receipt(
diff --git a/synapse/handlers/room.py b/synapse/handlers/room.py
index 579b1b93c5..64656fda22 100644
--- a/synapse/handlers/room.py
+++ b/synapse/handlers/room.py
@@ -87,7 +87,7 @@ class RoomCreationHandler(BaseHandler):
         self.config = hs.config
 
         # Room state based off defined presets
-        self._presets_dict = {
+        self._presets_dict: Dict[str, Dict[str, Any]] = {
             RoomCreationPreset.PRIVATE_CHAT: {
                 "join_rules": JoinRules.INVITE,
                 "history_visibility": HistoryVisibility.SHARED,
@@ -109,7 +109,7 @@ class RoomCreationHandler(BaseHandler):
                 "guest_can_join": False,
                 "power_level_content_override": {},
             },
-        }  # type: Dict[str, Dict[str, Any]]
+        }
 
         # Modify presets to selectively enable encryption by default per homeserver config
         for preset_name, preset_config in self._presets_dict.items():
@@ -127,9 +127,9 @@ class RoomCreationHandler(BaseHandler):
         # If a user tries to update the same room multiple times in quick
         # succession, only process the first attempt and return its result to
         # subsequent requests
-        self._upgrade_response_cache = ResponseCache(
+        self._upgrade_response_cache: ResponseCache[Tuple[str, str]] = ResponseCache(
             hs.get_clock(), "room_upgrade", timeout_ms=FIVE_MINUTES_IN_MS
-        )  # type: ResponseCache[Tuple[str, str]]
+        )
         self._server_notices_mxid = hs.config.server_notices_mxid
 
         self.third_party_event_rules = hs.get_third_party_event_rules()
@@ -377,10 +377,10 @@ class RoomCreationHandler(BaseHandler):
         if not await self.spam_checker.user_may_create_room(user_id):
             raise SynapseError(403, "You are not permitted to create rooms")
 
-        creation_content = {
+        creation_content: JsonDict = {
             "room_version": new_room_version.identifier,
             "predecessor": {"room_id": old_room_id, "event_id": tombstone_event_id},
-        }  # type: JsonDict
+        }
 
         # Check if old room was non-federatable
 
@@ -936,7 +936,7 @@ class RoomCreationHandler(BaseHandler):
                 etype=EventTypes.PowerLevels, content=pl_content
             )
         else:
-            power_level_content = {
+            power_level_content: JsonDict = {
                 "users": {creator_id: 100},
                 "users_default": 0,
                 "events": {
@@ -955,7 +955,7 @@ class RoomCreationHandler(BaseHandler):
                 "kick": 50,
                 "redact": 50,
                 "invite": 50,
-            }  # type: JsonDict
+            }
 
             if config["original_invitees_have_ops"]:
                 for invitee in invite_list:
diff --git a/synapse/handlers/room_list.py b/synapse/handlers/room_list.py
index c6bfa5451f..6284bcdfbc 100644
--- a/synapse/handlers/room_list.py
+++ b/synapse/handlers/room_list.py
@@ -47,12 +47,12 @@ class RoomListHandler(BaseHandler):
     def __init__(self, hs: "HomeServer"):
         super().__init__(hs)
         self.enable_room_list_search = hs.config.enable_room_list_search
-        self.response_cache = ResponseCache(
-            hs.get_clock(), "room_list"
-        )  # type: ResponseCache[Tuple[Optional[int], Optional[str], Optional[ThirdPartyInstanceID]]]
-        self.remote_response_cache = ResponseCache(
-            hs.get_clock(), "remote_room_list", timeout_ms=30 * 1000
-        )  # type: ResponseCache[Tuple[str, Optional[int], Optional[str], bool, Optional[str]]]
+        self.response_cache: ResponseCache[
+            Tuple[Optional[int], Optional[str], Optional[ThirdPartyInstanceID]]
+        ] = ResponseCache(hs.get_clock(), "room_list")
+        self.remote_response_cache: ResponseCache[
+            Tuple[str, Optional[int], Optional[str], bool, Optional[str]]
+        ] = ResponseCache(hs.get_clock(), "remote_room_list", timeout_ms=30 * 1000)
 
     async def get_local_public_room_list(
         self,
@@ -139,10 +139,10 @@ class RoomListHandler(BaseHandler):
         if since_token:
             batch_token = RoomListNextBatch.from_token(since_token)
 
-            bounds = (
+            bounds: Optional[Tuple[int, str]] = (
                 batch_token.last_joined_members,
                 batch_token.last_room_id,
-            )  # type: Optional[Tuple[int, str]]
+            )
             forwards = batch_token.direction_is_forward
             has_batch_token = True
         else:
@@ -182,7 +182,7 @@ class RoomListHandler(BaseHandler):
 
         results = [build_room_entry(r) for r in results]
 
-        response = {}  # type: JsonDict
+        response: JsonDict = {}
         num_results = len(results)
         if limit is not None:
             more_to_come = num_results == probing_limit
diff --git a/synapse/handlers/saml.py b/synapse/handlers/saml.py
index 80ba65b9e0..72f54c9403 100644
--- a/synapse/handlers/saml.py
+++ b/synapse/handlers/saml.py
@@ -83,7 +83,7 @@ class SamlHandler(BaseHandler):
         self.unstable_idp_brand = None
 
         # a map from saml session id to Saml2SessionData object
-        self._outstanding_requests_dict = {}  # type: Dict[str, Saml2SessionData]
+        self._outstanding_requests_dict: Dict[str, Saml2SessionData] = {}
 
         self._sso_handler = hs.get_sso_handler()
         self._sso_handler.register_identity_provider(self)
@@ -386,10 +386,10 @@ def dot_replace_for_mxid(username: str) -> str:
     return username
 
 
-MXID_MAPPER_MAP = {
+MXID_MAPPER_MAP: Dict[str, Callable[[str], str]] = {
     "hexencode": map_username_to_mxid_localpart,
     "dotreplace": dot_replace_for_mxid,
-}  # type: Dict[str, Callable[[str], str]]
+}
 
 
 @attr.s
diff --git a/synapse/handlers/search.py b/synapse/handlers/search.py
index 4e718d3f63..8226d6f5a1 100644
--- a/synapse/handlers/search.py
+++ b/synapse/handlers/search.py
@@ -192,7 +192,7 @@ class SearchHandler(BaseHandler):
         # 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
         if search_filter.rooms:
-            historical_room_ids = []  # type: List[str]
+            historical_room_ids: List[str] = []
             for room_id in search_filter.rooms:
                 # Add any previous rooms to the search if they exist
                 ids = await self.get_old_rooms_from_upgraded_room(room_id)
@@ -216,9 +216,9 @@ class SearchHandler(BaseHandler):
         rank_map = {}  # event_id -> rank of event
         allowed_events = []
         # Holds result of grouping by room, if applicable
-        room_groups = {}  # type: Dict[str, JsonDict]
+        room_groups: Dict[str, JsonDict] = {}
         # Holds result of grouping by sender, if applicable
-        sender_group = {}  # type: Dict[str, JsonDict]
+        sender_group: Dict[str, JsonDict] = {}
 
         # Holds the next_batch for the entire result set if one of those exists
         global_next_batch = None
@@ -262,7 +262,7 @@ class SearchHandler(BaseHandler):
                 s["results"].append(e.event_id)
 
         elif order_by == "recent":
-            room_events = []  # type: List[EventBase]
+            room_events: List[EventBase] = []
             i = 0
 
             pagination_token = batch_token
diff --git a/synapse/handlers/space_summary.py b/synapse/handlers/space_summary.py
index 366e6211e5..5f7d4602bd 100644
--- a/synapse/handlers/space_summary.py
+++ b/synapse/handlers/space_summary.py
@@ -90,14 +90,14 @@ class SpaceSummaryHandler:
         room_queue = deque((_RoomQueueEntry(room_id, ()),))
 
         # rooms we have already processed
-        processed_rooms = set()  # type: Set[str]
+        processed_rooms: Set[str] = set()
 
         # events we have already processed. We don't necessarily have their event ids,
         # so instead we key on (room id, state key)
-        processed_events = set()  # type: Set[Tuple[str, str]]
+        processed_events: Set[Tuple[str, str]] = set()
 
-        rooms_result = []  # type: List[JsonDict]
-        events_result = []  # type: List[JsonDict]
+        rooms_result: List[JsonDict] = []
+        events_result: List[JsonDict] = []
 
         while room_queue and len(rooms_result) < MAX_ROOMS:
             queue_entry = room_queue.popleft()
@@ -272,10 +272,10 @@ class SpaceSummaryHandler:
         # the set of rooms that we should not walk further. Initialise it with the
         # excluded-rooms list; we will add other rooms as we process them so that
         # we do not loop.
-        processed_rooms = set(exclude_rooms)  # type: Set[str]
+        processed_rooms: Set[str] = set(exclude_rooms)
 
-        rooms_result = []  # type: List[JsonDict]
-        events_result = []  # type: List[JsonDict]
+        rooms_result: List[JsonDict] = []
+        events_result: List[JsonDict] = []
 
         while room_queue and len(rooms_result) < MAX_ROOMS:
             room_id = room_queue.popleft()
@@ -353,7 +353,7 @@ class SpaceSummaryHandler:
             max_children = MAX_ROOMS_PER_SPACE
 
         now = self._clock.time_msec()
-        events_result = []  # type: List[JsonDict]
+        events_result: List[JsonDict] = []
         for edge_event in itertools.islice(child_events, max_children):
             events_result.append(
                 await self._event_serializer.serialize_event(
diff --git a/synapse/handlers/sso.py b/synapse/handlers/sso.py
index 0b297e54c4..1b855a685c 100644
--- a/synapse/handlers/sso.py
+++ b/synapse/handlers/sso.py
@@ -202,10 +202,10 @@ class SsoHandler:
         self._mapping_lock = Linearizer(name="sso_user_mapping", clock=hs.get_clock())
 
         # a map from session id to session data
-        self._username_mapping_sessions = {}  # type: Dict[str, UsernameMappingSession]
+        self._username_mapping_sessions: Dict[str, UsernameMappingSession] = {}
 
         # map from idp_id to SsoIdentityProvider
-        self._identity_providers = {}  # type: Dict[str, SsoIdentityProvider]
+        self._identity_providers: Dict[str, SsoIdentityProvider] = {}
 
         self._consent_at_registration = hs.config.consent.user_consent_at_registration
 
@@ -296,7 +296,7 @@ class SsoHandler:
             )
 
         # if the client chose an IdP, use that
-        idp = None  # type: Optional[SsoIdentityProvider]
+        idp: Optional[SsoIdentityProvider] = None
         if idp_id:
             idp = self._identity_providers.get(idp_id)
             if not idp:
@@ -669,9 +669,9 @@ class SsoHandler:
             remote_user_id,
         )
 
-        user_id_to_verify = await self._auth_handler.get_session_data(
+        user_id_to_verify: str = await self._auth_handler.get_session_data(
             ui_auth_session_id, UIAuthSessionDataConstants.REQUEST_USER_ID
-        )  # type: str
+        )
 
         if not user_id:
             logger.warning(
@@ -793,7 +793,7 @@ class SsoHandler:
         session.use_display_name = use_display_name
 
         emails_from_idp = set(session.emails)
-        filtered_emails = set()  # type: Set[str]
+        filtered_emails: Set[str] = set()
 
         # we iterate through the list rather than just building a set conjunction, so
         # that we can log attempts to use unknown addresses
diff --git a/synapse/handlers/stats.py b/synapse/handlers/stats.py
index 814d08efcb..3fd89af2a4 100644
--- a/synapse/handlers/stats.py
+++ b/synapse/handlers/stats.py
@@ -49,7 +49,7 @@ class StatsHandler:
         self.stats_enabled = hs.config.stats_enabled
 
         # The current position in the current_state_delta stream
-        self.pos = None  # type: Optional[int]
+        self.pos: Optional[int] = None
 
         # Guard to ensure we only process deltas one at a time
         self._is_processing = False
@@ -131,10 +131,10 @@ class StatsHandler:
             mapping from room/user ID to changes in the various fields.
         """
 
-        room_to_stats_deltas = {}  # type: Dict[str, CounterType[str]]
-        user_to_stats_deltas = {}  # type: Dict[str, CounterType[str]]
+        room_to_stats_deltas: Dict[str, CounterType[str]] = {}
+        user_to_stats_deltas: Dict[str, CounterType[str]] = {}
 
-        room_to_state_updates = {}  # type: Dict[str, Dict[str, Any]]
+        room_to_state_updates: Dict[str, Dict[str, Any]] = {}
 
         for delta in deltas:
             typ = delta["type"]
@@ -164,7 +164,7 @@ class StatsHandler:
                 )
                 continue
 
-            event_content = {}  # type: JsonDict
+            event_content: JsonDict = {}
 
             if event_id is not None:
                 event = await self.store.get_event(event_id, allow_none=True)
diff --git a/synapse/handlers/sync.py b/synapse/handlers/sync.py
index b9a0361059..722c4ae670 100644
--- a/synapse/handlers/sync.py
+++ b/synapse/handlers/sync.py
@@ -278,12 +278,14 @@ class SyncHandler:
         self.state_store = self.storage.state
 
         # ExpiringCache((User, Device)) -> LruCache(user_id => event_id)
-        self.lazy_loaded_members_cache = ExpiringCache(
+        self.lazy_loaded_members_cache: ExpiringCache[
+            Tuple[str, Optional[str]], LruCache[str, str]
+        ] = ExpiringCache(
             "lazy_loaded_members_cache",
             self.clock,
             max_len=0,
             expiry_ms=LAZY_LOADED_MEMBERS_CACHE_MAX_AGE,
-        )  # type: ExpiringCache[Tuple[str, Optional[str]], LruCache[str, str]]
+        )
 
     async def wait_for_sync_for_user(
         self,
@@ -440,7 +442,7 @@ class SyncHandler:
             )
             now_token = now_token.copy_and_replace("typing_key", typing_key)
 
-            ephemeral_by_room = {}  # type: JsonDict
+            ephemeral_by_room: JsonDict = {}
 
             for event in typing:
                 # we want to exclude the room_id from the event, but modifying the
@@ -502,7 +504,7 @@ class SyncHandler:
                 # We check if there are any state events, if there are then we pass
                 # all current state events to the filter_events function. This is to
                 # ensure that we always include current state in the timeline
-                current_state_ids = frozenset()  # type: FrozenSet[str]
+                current_state_ids: FrozenSet[str] = frozenset()
                 if any(e.is_state() for e in recents):
                     current_state_ids_map = await self.store.get_current_state_ids(
                         room_id
@@ -783,9 +785,9 @@ class SyncHandler:
     def get_lazy_loaded_members_cache(
         self, cache_key: Tuple[str, Optional[str]]
     ) -> LruCache[str, str]:
-        cache = self.lazy_loaded_members_cache.get(
+        cache: Optional[LruCache[str, str]] = self.lazy_loaded_members_cache.get(
             cache_key
-        )  # type: Optional[LruCache[str, str]]
+        )
         if cache is None:
             logger.debug("creating LruCache for %r", cache_key)
             cache = LruCache(LAZY_LOADED_MEMBERS_CACHE_MAX_SIZE)
@@ -984,7 +986,7 @@ class SyncHandler:
                     if t[0] == EventTypes.Member:
                         cache.set(t[1], event_id)
 
-        state = {}  # type: Dict[str, EventBase]
+        state: Dict[str, EventBase] = {}
         if state_ids:
             state = await self.store.get_events(list(state_ids.values()))
 
@@ -1088,8 +1090,8 @@ class SyncHandler:
 
         logger.debug("Fetching OTK data")
         device_id = sync_config.device_id
-        one_time_key_counts = {}  # type: JsonDict
-        unused_fallback_key_types = []  # type: List[str]
+        one_time_key_counts: JsonDict = {}
+        unused_fallback_key_types: List[str] = []
         if device_id:
             one_time_key_counts = await self.store.count_e2e_one_time_keys(
                 user_id, device_id
@@ -1437,7 +1439,7 @@ class SyncHandler:
         )
 
         if block_all_room_ephemeral:
-            ephemeral_by_room = {}  # type: Dict[str, List[JsonDict]]
+            ephemeral_by_room: Dict[str, List[JsonDict]] = {}
         else:
             now_token, ephemeral_by_room = await self.ephemeral_by_room(
                 sync_result_builder,
@@ -1468,7 +1470,7 @@ class SyncHandler:
 
         # If there is ignored users account data and it matches the proper type,
         # then use it.
-        ignored_users = frozenset()  # type: FrozenSet[str]
+        ignored_users: FrozenSet[str] = frozenset()
         if ignored_account_data:
             ignored_users_data = ignored_account_data.get("ignored_users", {})
             if isinstance(ignored_users_data, dict):
@@ -1586,7 +1588,7 @@ class SyncHandler:
             user_id, since_token.room_key, now_token.room_key
         )
 
-        mem_change_events_by_room_id = {}  # type: Dict[str, List[EventBase]]
+        mem_change_events_by_room_id: Dict[str, List[EventBase]] = {}
         for event in rooms_changed:
             mem_change_events_by_room_id.setdefault(event.room_id, []).append(event)
 
@@ -1722,7 +1724,7 @@ class SyncHandler:
                 # This is all screaming out for a refactor, as the logic here is
                 # subtle and the moving parts numerous.
                 if leave_event.internal_metadata.is_out_of_band_membership():
-                    batch_events = [leave_event]  # type: Optional[List[EventBase]]
+                    batch_events: Optional[List[EventBase]] = [leave_event]
                 else:
                     batch_events = None
 
@@ -1971,7 +1973,7 @@ class SyncHandler:
             room_id, batch, sync_config, since_token, now_token, full_state=full_state
         )
 
-        summary = {}  # type: Optional[JsonDict]
+        summary: Optional[JsonDict] = {}
 
         # we include a summary in room responses when we're lazy loading
         # members (as the client otherwise doesn't have enough info to form
@@ -1995,7 +1997,7 @@ class SyncHandler:
             )
 
         if room_builder.rtype == "joined":
-            unread_notifications = {}  # type: Dict[str, int]
+            unread_notifications: Dict[str, int] = {}
             room_sync = JoinedSyncResult(
                 room_id=room_id,
                 timeline=batch,
diff --git a/synapse/handlers/typing.py b/synapse/handlers/typing.py
index c0a8364755..0cb651a400 100644
--- a/synapse/handlers/typing.py
+++ b/synapse/handlers/typing.py
@@ -68,11 +68,11 @@ class FollowerTypingHandler:
             )
 
         # map room IDs to serial numbers
-        self._room_serials = {}  # type: Dict[str, int]
+        self._room_serials: Dict[str, int] = {}
         # map room IDs to sets of users currently typing
-        self._room_typing = {}  # type: Dict[str, Set[str]]
+        self._room_typing: Dict[str, Set[str]] = {}
 
-        self._member_last_federation_poke = {}  # type: Dict[RoomMember, int]
+        self._member_last_federation_poke: Dict[RoomMember, int] = {}
         self.wheel_timer = WheelTimer(bucket_size=5000)
         self._latest_room_serial = 0
 
@@ -217,7 +217,7 @@ class TypingWriterHandler(FollowerTypingHandler):
         hs.get_distributor().observe("user_left_room", self.user_left_room)
 
         # clock time we expect to stop
-        self._member_typing_until = {}  # type: Dict[RoomMember, int]
+        self._member_typing_until: Dict[RoomMember, int] = {}
 
         # caches which room_ids changed at which serials
         self._typing_stream_change_cache = StreamChangeCache(
@@ -405,9 +405,9 @@ class TypingWriterHandler(FollowerTypingHandler):
         if last_id == current_id:
             return [], current_id, False
 
-        changed_rooms = self._typing_stream_change_cache.get_all_entities_changed(
-            last_id
-        )  # type: Optional[Iterable[str]]
+        changed_rooms: Optional[
+            Iterable[str]
+        ] = self._typing_stream_change_cache.get_all_entities_changed(last_id)
 
         if changed_rooms is None:
             changed_rooms = self._room_serials
diff --git a/synapse/handlers/user_directory.py b/synapse/handlers/user_directory.py
index dacc4f3076..6edb1da50a 100644
--- a/synapse/handlers/user_directory.py
+++ b/synapse/handlers/user_directory.py
@@ -52,7 +52,7 @@ class UserDirectoryHandler(StateDeltasHandler):
         self.search_all_users = hs.config.user_directory_search_all_users
         self.spam_checker = hs.get_spam_checker()
         # The current position in the current_state_delta stream
-        self.pos = None  # type: Optional[int]
+        self.pos: Optional[int] = None
 
         # Guard to ensure we only process deltas one at a time
         self._is_processing = False
diff --git a/synapse/rest/admin/rooms.py b/synapse/rest/admin/rooms.py
index 3c51a742bf..40ee33646c 100644
--- a/synapse/rest/admin/rooms.py
+++ b/synapse/rest/admin/rooms.py
@@ -402,9 +402,9 @@ class JoinRoomAliasServlet(ResolveRoomIdMixin, RestServlet):
 
         # Get the room ID from the identifier.
         try:
-            remote_room_hosts = [
+            remote_room_hosts: Optional[List[str]] = [
                 x.decode("ascii") for x in request.args[b"server_name"]
-            ]  # type: Optional[List[str]]
+            ]
         except Exception:
             remote_room_hosts = None
         room_id, remote_room_hosts = await self.resolve_room_id(
@@ -659,9 +659,7 @@ class RoomEventContextServlet(RestServlet):
         filter_str = parse_string(request, "filter", encoding="utf-8")
         if filter_str:
             filter_json = urlparse.unquote(filter_str)
-            event_filter = Filter(
-                json_decoder.decode(filter_json)
-            )  # type: Optional[Filter]
+            event_filter: Optional[Filter] = Filter(json_decoder.decode(filter_json))
         else:
             event_filter = None
 
diff --git a/synapse/rest/admin/users.py b/synapse/rest/admin/users.py
index 06e6ccee42..589e47fa47 100644
--- a/synapse/rest/admin/users.py
+++ b/synapse/rest/admin/users.py
@@ -357,7 +357,7 @@ class UserRegisterServlet(RestServlet):
     def __init__(self, hs: "HomeServer"):
         self.auth_handler = hs.get_auth_handler()
         self.reactor = hs.get_reactor()
-        self.nonces = {}  # type: Dict[str, int]
+        self.nonces: Dict[str, int] = {}
         self.hs = hs
 
     def _clear_old_nonces(self):
diff --git a/synapse/rest/client/v1/login.py b/synapse/rest/client/v1/login.py
index cbcb60fe31..99d02cb355 100644
--- a/synapse/rest/client/v1/login.py
+++ b/synapse/rest/client/v1/login.py
@@ -121,7 +121,7 @@ class LoginRestServlet(RestServlet):
             flows.append({"type": LoginRestServlet.CAS_TYPE})
 
         if self.cas_enabled or self.saml2_enabled or self.oidc_enabled:
-            sso_flow = {
+            sso_flow: JsonDict = {
                 "type": LoginRestServlet.SSO_TYPE,
                 "identity_providers": [
                     _get_auth_flow_dict_for_idp(
@@ -129,7 +129,7 @@ class LoginRestServlet(RestServlet):
                     )
                     for idp in self._sso_handler.get_identity_providers().values()
                 ],
-            }  # type: JsonDict
+            }
 
             if self._msc2858_enabled:
                 # backwards-compatibility support for clients which don't
@@ -447,7 +447,7 @@ def _get_auth_flow_dict_for_idp(
         use_unstable_brands: whether we should use brand identifiers suitable
            for the unstable API
     """
-    e = {"id": idp.idp_id, "name": idp.idp_name}  # type: JsonDict
+    e: JsonDict = {"id": idp.idp_id, "name": idp.idp_name}
     if idp.idp_icon:
         e["icon"] = idp.idp_icon
     if idp.idp_brand:
@@ -561,7 +561,7 @@ class SsoRedirectServlet(RestServlet):
             finish_request(request)
             return
 
-        args = request.args  # type: Dict[bytes, List[bytes]]  # type: ignore
+        args: Dict[bytes, List[bytes]] = request.args  # type: ignore
         client_redirect_url = parse_bytes_from_args(args, "redirectUrl", required=True)
         sso_url = await self._sso_handler.handle_redirect_request(
             request,
diff --git a/synapse/rest/client/v1/room.py b/synapse/rest/client/v1/room.py
index ebf4e32230..31a1193cd3 100644
--- a/synapse/rest/client/v1/room.py
+++ b/synapse/rest/client/v1/room.py
@@ -783,7 +783,7 @@ class PublicRoomListRestServlet(TransactionRestServlet):
         server = parse_string(request, "server", default=None)
         content = parse_json_object_from_request(request)
 
-        limit = int(content.get("limit", 100))  # type: Optional[int]
+        limit: Optional[int] = int(content.get("limit", 100))
         since_token = content.get("since", None)
         search_filter = content.get("filter", None)
 
@@ -929,9 +929,7 @@ class RoomMessageListRestServlet(RestServlet):
         filter_str = parse_string(request, "filter", encoding="utf-8")
         if filter_str:
             filter_json = urlparse.unquote(filter_str)
-            event_filter = Filter(
-                json_decoder.decode(filter_json)
-            )  # type: Optional[Filter]
+            event_filter: Optional[Filter] = Filter(json_decoder.decode(filter_json))
             if (
                 event_filter
                 and event_filter.filter_json.get("event_format", "client")
@@ -1044,9 +1042,7 @@ class RoomEventContextServlet(RestServlet):
         filter_str = parse_string(request, "filter", encoding="utf-8")
         if filter_str:
             filter_json = urlparse.unquote(filter_str)
-            event_filter = Filter(
-                json_decoder.decode(filter_json)
-            )  # type: Optional[Filter]
+            event_filter: Optional[Filter] = Filter(json_decoder.decode(filter_json))
         else:
             event_filter = None
 
diff --git a/synapse/rest/client/v2_alpha/sendtodevice.py b/synapse/rest/client/v2_alpha/sendtodevice.py
index f8dcee603c..d537d811d8 100644
--- a/synapse/rest/client/v2_alpha/sendtodevice.py
+++ b/synapse/rest/client/v2_alpha/sendtodevice.py
@@ -59,7 +59,7 @@ class SendToDeviceRestServlet(servlet.RestServlet):
             requester, message_type, content["messages"]
         )
 
-        response = (200, {})  # type: Tuple[int, dict]
+        response: Tuple[int, dict] = (200, {})
         return response
 
 
diff --git a/synapse/rest/consent/consent_resource.py b/synapse/rest/consent/consent_resource.py
index e52570cd8e..4282e2b228 100644
--- a/synapse/rest/consent/consent_resource.py
+++ b/synapse/rest/consent/consent_resource.py
@@ -117,7 +117,7 @@ class ConsentResource(DirectServeHtmlResource):
         has_consented = False
         public_version = username == ""
         if not public_version:
-            args = request.args  # type: Dict[bytes, List[bytes]]
+            args: Dict[bytes, List[bytes]] = request.args
             userhmac_bytes = parse_bytes_from_args(args, "h", required=True)
 
             self._check_hash(username, userhmac_bytes)
@@ -154,7 +154,7 @@ class ConsentResource(DirectServeHtmlResource):
         """
         version = parse_string(request, "v", required=True)
         username = parse_string(request, "u", required=True)
-        args = request.args  # type: Dict[bytes, List[bytes]]
+        args: Dict[bytes, List[bytes]] = request.args
         userhmac = parse_bytes_from_args(args, "h", required=True)
 
         self._check_hash(username, userhmac)
diff --git a/synapse/rest/key/v2/remote_key_resource.py b/synapse/rest/key/v2/remote_key_resource.py
index d56a1ae482..63a40b1852 100644
--- a/synapse/rest/key/v2/remote_key_resource.py
+++ b/synapse/rest/key/v2/remote_key_resource.py
@@ -97,7 +97,7 @@ class RemoteKey(DirectServeJsonResource):
     async def _async_render_GET(self, request):
         if len(request.postpath) == 1:
             (server,) = request.postpath
-            query = {server.decode("ascii"): {}}  # type: dict
+            query: dict = {server.decode("ascii"): {}}
         elif len(request.postpath) == 2:
             server, key_id = request.postpath
             minimum_valid_until_ts = parse_integer(request, "minimum_valid_until_ts")
@@ -141,7 +141,7 @@ class RemoteKey(DirectServeJsonResource):
         time_now_ms = self.clock.time_msec()
 
         # Note that the value is unused.
-        cache_misses = {}  # type: Dict[str, Dict[str, int]]
+        cache_misses: Dict[str, Dict[str, int]] = {}
         for (server_name, key_id, _), 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 0fb4cd81f1..90364ebcf7 100644
--- a/synapse/rest/media/v1/_base.py
+++ b/synapse/rest/media/v1/_base.py
@@ -49,7 +49,7 @@ TEXT_CONTENT_TYPES = [
 def parse_media_id(request: Request) -> Tuple[str, str, Optional[str]]:
     try:
         # The type on postpath seems incorrect in Twisted 21.2.0.
-        postpath = request.postpath  # type: List[bytes]  # type: ignore
+        postpath: List[bytes] = request.postpath  # type: ignore
         assert postpath
 
         # This allows users to append e.g. /test.png to the URL. Useful for
diff --git a/synapse/rest/media/v1/media_repository.py b/synapse/rest/media/v1/media_repository.py
index 21c43c340c..4f702f890c 100644
--- a/synapse/rest/media/v1/media_repository.py
+++ b/synapse/rest/media/v1/media_repository.py
@@ -78,16 +78,16 @@ class MediaRepository:
 
         Thumbnailer.set_limits(self.max_image_pixels)
 
-        self.primary_base_path = hs.config.media_store_path  # type: str
-        self.filepaths = MediaFilePaths(self.primary_base_path)  # type: MediaFilePaths
+        self.primary_base_path: str = hs.config.media_store_path
+        self.filepaths: MediaFilePaths = MediaFilePaths(self.primary_base_path)
 
         self.dynamic_thumbnails = hs.config.dynamic_thumbnails
         self.thumbnail_requirements = hs.config.thumbnail_requirements
 
         self.remote_media_linearizer = Linearizer(name="media_remote")
 
-        self.recently_accessed_remotes = set()  # type: Set[Tuple[str, str]]
-        self.recently_accessed_locals = set()  # type: Set[str]
+        self.recently_accessed_remotes: Set[Tuple[str, str]] = set()
+        self.recently_accessed_locals: Set[str] = set()
 
         self.federation_domain_whitelist = hs.config.federation_domain_whitelist
 
@@ -711,7 +711,7 @@ class MediaRepository:
 
         # We deduplicate the thumbnail sizes by ignoring the cropped versions if
         # they have the same dimensions of a scaled one.
-        thumbnails = {}  # type: Dict[Tuple[int, int, str], str]
+        thumbnails: Dict[Tuple[int, int, str], str] = {}
         for r_width, r_height, r_method, r_type in requirements:
             if r_method == "crop":
                 thumbnails.setdefault((r_width, r_height, r_type), r_method)
diff --git a/synapse/rest/media/v1/media_storage.py b/synapse/rest/media/v1/media_storage.py
index c7fd97c46c..56cdc1b4ed 100644
--- a/synapse/rest/media/v1/media_storage.py
+++ b/synapse/rest/media/v1/media_storage.py
@@ -191,7 +191,7 @@ class MediaStorage:
 
         for provider in self.storage_providers:
             for path in paths:
-                res = await provider.fetch(path, file_info)  # type: Any
+                res: Any = await provider.fetch(path, file_info)
                 if res:
                     logger.debug("Streaming %s from %s", path, provider)
                     return res
@@ -233,7 +233,7 @@ class MediaStorage:
             os.makedirs(dirname)
 
         for provider in self.storage_providers:
-            res = await provider.fetch(path, file_info)  # type: Any
+            res: Any = await provider.fetch(path, file_info)
             if res:
                 with res:
                     consumer = BackgroundFileConsumer(
diff --git a/synapse/rest/media/v1/preview_url_resource.py b/synapse/rest/media/v1/preview_url_resource.py
index 0adfb1a70f..8e7fead3a2 100644
--- a/synapse/rest/media/v1/preview_url_resource.py
+++ b/synapse/rest/media/v1/preview_url_resource.py
@@ -169,12 +169,12 @@ class PreviewUrlResource(DirectServeJsonResource):
 
         # memory cache mapping urls to an ObservableDeferred returning
         # JSON-encoded OG metadata
-        self._cache = ExpiringCache(
+        self._cache: ExpiringCache[str, ObservableDeferred] = ExpiringCache(
             cache_name="url_previews",
             clock=self.clock,
             # don't spider URLs more often than once an hour
             expiry_ms=ONE_HOUR,
-        )  # type: ExpiringCache[str, ObservableDeferred]
+        )
 
         if self._worker_run_media_background_jobs:
             self._cleaner_loop = self.clock.looping_call(
@@ -460,7 +460,7 @@ class PreviewUrlResource(DirectServeJsonResource):
         file_info = FileInfo(server_name=None, file_id=file_id, url_cache=True)
 
         # If this URL can be accessed via oEmbed, use that instead.
-        url_to_download = url  # type: Optional[str]
+        url_to_download: Optional[str] = url
         oembed_url = self._get_oembed_url(url)
         if oembed_url:
             # The result might be a new URL to download, or it might be HTML content.
@@ -788,7 +788,7 @@ def _calc_og(tree: "etree.Element", media_uri: str) -> Dict[str, Optional[str]]:
     # "og:video:height" : "720",
     # "og:video:secure_url": "https://www.youtube.com/v/LXDBoHyjmtw?version=3",
 
-    og = {}  # type: Dict[str, Optional[str]]
+    og: Dict[str, Optional[str]] = {}
     for tag in tree.xpath("//*/meta[starts-with(@property, 'og:')]"):
         if "content" in tag.attrib:
             # if we've got more than 50 tags, someone is taking the piss
diff --git a/synapse/rest/media/v1/upload_resource.py b/synapse/rest/media/v1/upload_resource.py
index 62dc4aae2d..146adca8f1 100644
--- a/synapse/rest/media/v1/upload_resource.py
+++ b/synapse/rest/media/v1/upload_resource.py
@@ -61,11 +61,11 @@ class UploadResource(DirectServeJsonResource):
                 errcode=Codes.TOO_LARGE,
             )
 
-        args = request.args  # type: Dict[bytes, List[bytes]]  # type: ignore
+        args: Dict[bytes, List[bytes]] = request.args  # type: ignore
         upload_name_bytes = parse_bytes_from_args(args, "filename")
         if upload_name_bytes:
             try:
-                upload_name = upload_name_bytes.decode("utf8")  # type: Optional[str]
+                upload_name: Optional[str] = upload_name_bytes.decode("utf8")
             except UnicodeDecodeError:
                 raise SynapseError(
                     msg="Invalid UTF-8 filename parameter: %r" % (upload_name), code=400
@@ -89,7 +89,7 @@ class UploadResource(DirectServeJsonResource):
         # TODO(markjh): parse content-dispostion
 
         try:
-            content = request.content  # type: IO  # type: ignore
+            content: IO = request.content  # type: ignore
             content_uri = await self.media_repo.create_content(
                 media_type, upload_name, content, content_length, requester.user
             )
diff --git a/synapse/rest/synapse/client/pick_username.py b/synapse/rest/synapse/client/pick_username.py
index 9b002cc15e..ab24ec0a8e 100644
--- a/synapse/rest/synapse/client/pick_username.py
+++ b/synapse/rest/synapse/client/pick_username.py
@@ -118,9 +118,9 @@ class AccountDetailsResource(DirectServeHtmlResource):
             use_display_name = parse_boolean(request, "use_display_name", default=False)
 
             try:
-                emails_to_use = [
+                emails_to_use: List[str] = [
                     val.decode("utf-8") for val in request.args.get(b"use_email", [])
-                ]  # type: List[str]
+                ]
             except ValueError:
                 raise SynapseError(400, "Query parameter use_email must be utf-8")
         except SynapseError as e: