Review comments

1 files changed, 9 insertions, 11 deletions

diff --git a/synapse/events/utils.py b/synapse/events/utils.py
index f4b21ca517..5bbaef8187 100644
--- a/synapse/events/utils.py
+++ b/synapse/events/utils.py
@@ -145,9 +145,7 @@ def _copy_field(src, dst, field):
     # the empty objects if the key didn't exist.
     sub_out_dict = dst
     for sub_field in field:
-        if sub_field not in sub_out_dict:
-            sub_out_dict[sub_field] = {}
-        sub_out_dict = sub_out_dict[sub_field]
+        sub_out_dict = sub_out_dict.setdefault(sub_field, {})
     sub_out_dict[key_to_move] = sub_dict[key_to_move]
 
 
@@ -176,12 +174,10 @@ def only_fields(dictionary, fields):
     split_fields = [SPLIT_FIELD_REGEX.split(f) for f in fields]
 
     # for each element of the output array of arrays:
-    # remove escaping so we can use the right key names. This purposefully avoids
-    # using list comprehensions to avoid needless allocations as this may be called
-    # on a lot of events.
-    for field_array in split_fields:
-        for i, field in enumerate(field_array):
-            field_array[i] = field.replace(r'\.', r'.')
+    # remove escaping so we can use the right key names.
+    split_fields[:] = [
+        [f.replace(r'\.', r'.') for f in field_array] for field_array in split_fields
+    ]
 
     output = {}
     for field_array in split_fields:
@@ -258,8 +254,10 @@ def serialize_event(e, time_now_ms, as_client_event=True,
     if as_client_event:
         d = event_format(d)
 
-    if (only_event_fields and isinstance(only_event_fields, list) and
-            all(isinstance(f, basestring) for f in only_event_fields)):
+    if only_event_fields:
+        if (not isinstance(only_event_fields, list) or
+                not all(isinstance(f, basestring) for f in only_event_fields)):
+            raise TypeError("only_event_fields must be a list of strings")
         d = only_fields(d, only_event_fields)
 
     return d