use %r to __repr__ objects

This avoids calculating __repr__ unless we are going to log.

synapse/federation/federation_client.py

@@ -196,7 +196,7 @@ class FederationClient(FederationBase):
             dest, room_id, extremities, limit
         )
 
-        logger.debug("backfill transaction_data=%s", repr(transaction_data))
+        logger.debug("backfill transaction_data=%r", transaction_data)
 
         room_version = yield self.store.get_room_version(room_id)
         format_ver = room_version_to_event_format(room_version)

synapse/federation/transport/client.py

@@ -122,10 +122,10 @@ class TransportLayerClient(object):
             Deferred: Results in a dict received from the remote homeserver.
         """
         logger.debug(
-            "backfill dest=%s, room_id=%s, event_tuples=%s, limit=%s",
+            "backfill dest=%s, room_id=%s, event_tuples=%r, limit=%s",
             destination,
             room_id,
-            repr(event_tuples),
+            event_tuples,
             str(limit),
         )
 

synapse/storage/data_stores/main/event_federation.py

@@ -365,7 +365,7 @@ class EventFederationWorkerStore(EventsWorkerStore, SignatureWorkerStore, SQLBas
 
     def _get_backfill_events(self, txn, room_id, event_list, limit):
         logger.debug(
-            "_get_backfill_events: %s, %s, %s", room_id, repr(event_list), limit
+            "_get_backfill_events: %s, %r, %s", room_id, event_list, limit
         )
 
         event_results = set()