diff --git a/IPython/html/widgets/widget_container.py b/IPython/html/widgets/widget_container.py
index f8661fc..92a7f9c 100644
--- a/IPython/html/widgets/widget_container.py
+++ b/IPython/html/widgets/widget_container.py
@@ -45,7 +45,7 @@ class ContainerWidget(DOMWidget):
http://www.peterbe.com/plog/uniqifiers-benchmark
which provides the inspiration for using this implementation. Below
I've implemented the `f5` algorithm using Python comprehensions."""
- if new is not None and isinstance(new, list):
+ if new is not None:
seen = {}
def add_item(i):
seen[i.model_id] = True