From 521b0ab58d6e52842a9c93cc388089ad623b9c4b Mon Sep 17 00:00:00 2001
From: Dion Moult <dion@thinkmoult.com>
Date: Mon, 2 Sep 2024 17:35:43 +1000
Subject: [PATCH] Fix #5271. Prevent duplicate entries when getting a
 decomposition.

---
 .../ifcopenshell/util/element.py                   | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/src/ifcopenshell-python/ifcopenshell/util/element.py b/src/ifcopenshell-python/ifcopenshell/util/element.py
index 6024cfc347..bb29b476a5 100644
--- a/src/ifcopenshell-python/ifcopenshell/util/element.py
+++ b/src/ifcopenshell-python/ifcopenshell/util/element.py
@@ -947,7 +947,7 @@ def get_structure_referenced_elements(structure: ifcopenshell.entity_instance) -
     return referenced
 
 
-def get_decomposition(element: ifcopenshell.entity_instance, is_recursive=True) -> list[ifcopenshell.entity_instance]:
+def get_decomposition(element: ifcopenshell.entity_instance, is_recursive=True) -> set[ifcopenshell.entity_instance]:
     """
     Retrieves all subelements of an element based on the spatial decomposition
     hierarchy. This includes all subspaces and elements contained in subspaces,
@@ -966,29 +966,29 @@ def get_decomposition(element: ifcopenshell.entity_instance, is_recursive=True)
         decomposition = ifcopenshell.util.element.get_decomposition(element)
     """
     queue = [element]
-    results = []
+    results = set()
     while queue:
         element = queue.pop()
         for rel in getattr(element, "ContainsElements", []):
             related = rel.RelatedElements
             queue.extend(related)
-            results.extend(related)
+            results.update(related)
         for rel in getattr(element, "IsDecomposedBy", []):
             related = rel.RelatedObjects
             queue.extend(related)
-            results.extend(related)
+            results.update(related)
         for rel in getattr(element, "HasOpenings", []):
             related = rel.RelatedOpeningElement
             queue.append(related)
-            results.append(related)
+            results.add(related)
         for rel in getattr(element, "HasFillings", []):
             related = rel.RelatedBuildingElement
             queue.append(related)
-            results.append(related)
+            results.add(related)
         for rel in getattr(element, "IsNestedBy", []):
             related = rel.RelatedObjects
             queue.extend(related)
-            results.extend(related)
+            results.update(related)
         if not is_recursive:
             break
     return results