Locally import FrozenSet node to avoid circular import

astroid/helpers.py

@@ -236,12 +236,13 @@ def object_len(node, context=None):
         or if multiple nodes are inferred
     :rtype int: Integer length of node
     """
+    from astroid.objects import FrozenSet
     inferred_node = safe_infer(node, context=context)
     if inferred_node is None or inferred_node is util.Uninferable:
         raise exceptions.InferenceError(node=node)
     if inferred_node.qname() in ('builtins.str', 'builtins.bytes'):
         return len(inferred_node.value)
-    if isinstance(inferred_node, (nodes.List, nodes.Set, nodes.Tuple, nodes.FrozenSet)):
+    if isinstance(inferred_node, (nodes.List, nodes.Set, nodes.Tuple, FrozenSet)):
         return len(inferred_node.elts)
     if isinstance(inferred_node, nodes.Dict):
         return len(inferred_node.items)