Drop extra type check in _extract_serialize

distributed/protocol/serialize.py

@@ -1,6 +1,5 @@
 from array import array
 from functools import partial
-from itertools import repeat
 import traceback
 import importlib
 from enum import Enum
@@ -445,27 +444,32 @@ def extract_serialize(x):
     >>> extract_serialize(msg)
     ({'op': 'update'}, {('data',): <Serialize: 123>}, set())
     """
-    x2 = type(x)()
-    ser = {}
-    bytestrings = set()
-    _extract_serialize(x, x2, ser, bytestrings)
-    return x2, ser, bytestrings
-
-
-def _extract_serialize(x, x2, ser, bytestrings, path=()):
     typ_x = type(x)
     if typ_x is dict:
         x_items = x.items()
+        x2 = dict()
     elif typ_x is list:
         x_items = enumerate(x)
-        x2.extend(repeat(None, len(x)))
+        x2 = len(x) * [None]
+
+    ser = {}
+    bytestrings = set()
+    _extract_serialize(x, x_items, x2, ser, bytestrings)
+    return x2, ser, bytestrings
+
 
+def _extract_serialize(x, x_items, x2, ser, bytestrings, path=()):
     for k, v in x_items:
         path_k = path + (k,)
         typ_v = type(v)
-        if typ_v is dict or typ_v is list:
-            x2[k] = v2 = typ_v()
-            _extract_serialize(v, v2, ser, bytestrings, path_k)
+        if typ_v is dict:
+            v_items = v.items()
+            x2[k] = v2 = dict()
+            _extract_serialize(v, v_items, v2, ser, bytestrings, path_k)
+        elif typ_v is list:
+            v_items = enumerate(v)
+            x2[k] = v2 = len(v) * [None]
+            _extract_serialize(v, v_items, v2, ser, bytestrings, path_k)
         elif typ_v is Serialize or typ_v is Serialized:
             ser[path_k] = v
         elif (typ_v is bytes or typ_v is bytearray) and len(v) > 2 ** 16: