4 files changed, 10 insertions, 17 deletions
diff --git a/synapse/storage/databases/main/account_data.py b/synapse/storage/databases/main/account_data.py
index 4436b1a83d..5f1a2b9aa6 100644
--- a/synapse/storage/databases/main/account_data.py
+++ b/synapse/storage/databases/main/account_data.py
@@ -29,15 +29,13 @@ from synapse.util.caches.stream_change_cache import StreamChangeCache
 logger = logging.getLogger(__name__)
 
 
-class AccountDataWorkerStore(SQLBaseStore):
+# The ABCMeta metaclass ensures that it cannot be instantiated without
+# the abstract methods being implemented.
+class AccountDataWorkerStore(SQLBaseStore, metaclass=abc.ABCMeta):
     """This is an abstract base class where subclasses must implement
     `get_max_account_data_stream_id` which can be called in the initializer.
     """
 
-    # This ABCMeta metaclass ensures that we cannot be instantiated without
-    # the abstract methods being implemented.
-    __metaclass__ = abc.ABCMeta
-
     def __init__(self, database: DatabasePool, db_conn, hs):
         account_max = self.get_max_account_data_stream_id()
         self._account_data_stream_cache = StreamChangeCache(
diff --git a/synapse/storage/databases/main/push_rule.py b/synapse/storage/databases/main/push_rule.py
index 9790a31998..b7a8d34ce1 100644
--- a/synapse/storage/databases/main/push_rule.py
+++ b/synapse/storage/databases/main/push_rule.py
@@ -61,6 +61,8 @@ def _load_rules(rawrules, enabled_map, use_new_defaults=False):
     return rules
 
 
+# The ABCMeta metaclass ensures that it cannot be instantiated without
+# the abstract methods being implemented.
 class PushRulesWorkerStore(
     ApplicationServiceWorkerStore,
     ReceiptsWorkerStore,
@@ -68,15 +70,12 @@ class PushRulesWorkerStore(
     RoomMemberWorkerStore,
     EventsWorkerStore,
     SQLBaseStore,
+    metaclass=abc.ABCMeta,
 ):
     """This is an abstract base class where subclasses must implement
     `get_max_push_rules_stream_id` which can be called in the initializer.
     """
 
-    # This ABCMeta metaclass ensures that we cannot be instantiated without
-    # the abstract methods being implemented.
-    __metaclass__ = abc.ABCMeta
-
     def __init__(self, database: DatabasePool, db_conn, hs):
         super(PushRulesWorkerStore, self).__init__(database, db_conn, hs)
 
diff --git a/synapse/storage/databases/main/receipts.py b/synapse/storage/databases/main/receipts.py
index 4a0d5a320e..6568bddd81 100644
--- a/synapse/storage/databases/main/receipts.py
+++ b/synapse/storage/databases/main/receipts.py
@@ -31,15 +31,13 @@ from synapse.util.caches.stream_change_cache import StreamChangeCache
 logger = logging.getLogger(__name__)
 
 
-class ReceiptsWorkerStore(SQLBaseStore):
+# The ABCMeta metaclass ensures that it cannot be instantiated without
+# the abstract methods being implemented.
+class ReceiptsWorkerStore(SQLBaseStore, metaclass=abc.ABCMeta):
     """This is an abstract base class where subclasses must implement
     `get_max_receipt_stream_id` which can be called in the initializer.
     """
 
-    # This ABCMeta metaclass ensures that we cannot be instantiated without
-    # the abstract methods being implemented.
-    __metaclass__ = abc.ABCMeta
-
     def __init__(self, database: DatabasePool, db_conn, hs):
         super(ReceiptsWorkerStore, self).__init__(database, db_conn, hs)
 
diff --git a/synapse/storage/databases/main/stream.py b/synapse/storage/databases/main/stream.py
index 2e95518752..7dbe11513b 100644
--- a/synapse/storage/databases/main/stream.py
+++ b/synapse/storage/databases/main/stream.py
@@ -259,14 +259,12 @@ def filter_to_clause(event_filter: Optional[Filter]) -> Tuple[str, List[str]]:
     return " AND ".join(clauses), args
 
 
-class StreamWorkerStore(EventsWorkerStore, SQLBaseStore):
+class StreamWorkerStore(EventsWorkerStore, SQLBaseStore, metaclass=abc.ABCMeta):
     """This is an abstract base class where subclasses must implement
     `get_room_max_stream_ordering` and `get_room_min_stream_ordering`
     which can be called in the initializer.
     """
 
-    __metaclass__ = abc.ABCMeta
-
     def __init__(self, database: DatabasePool, db_conn, hs: "HomeServer"):
         super(StreamWorkerStore, self).__init__(database, db_conn, hs)