diff --git a/python/datastruct.py b/python/datastruct.py
index 22e0647..48df054 100644
--- a/python/datastruct.py
+++ b/python/datastruct.py
@@ -29,9 +29,14 @@ class UnionFindQueue(Generic[_NameT, _ElemT]):
     tracking added to it.
     """
 
+    __slots__ = ("name", "tree", "sub_queues", "split_nodes")
+
     class Node(Generic[_NameT2, _ElemT2]):
         """Node in a UnionFindQueue."""
 
+        __slots__ = ("owner", "data", "prio", "min_node", "height",
+                     "parent", "left", "right")
+
         def __init__(self,
                      owner: "UnionFindQueue[_NameT2, _ElemT2]",
                      data: _ElemT2,
@@ -688,6 +693,8 @@ class UnionFindQueue(Generic[_NameT, _ElemT]):
 class PriorityQueue(Generic[_ElemT]):
     """Priority queue based on a binary heap."""
 
+    __slots__ = ("heap", )
+
     class Node(Generic[_ElemT2]):
         """Node in the priority queue."""