You can now assign derived quantities from products to cost items

src/ifcopenshell-python/ifcopenshell/api/cost/assign_cost_item_product_quantities.py

@@ -0,0 +1,32 @@
+import ifcopenshell.api
+
+
+class Usecase:
+    def __init__(self, file, **settings):
+        self.file = file
+        self.settings = {"cost_item": None, "qto_name": "", "prop_name": ""}
+        for key, value in settings.items():
+            self.settings[key] = value
+
+    def execute(self):
+        self.quantities = set(self.settings["cost_item"].CostQuantities or [])
+        for control in self.settings["cost_item"].Controls or []:
+            for related_object in control.RelatedObjects:
+                self.add_quantity_from_related_object(related_object)
+        self.settings["cost_item"].CostQuantities = list(self.quantities)
+
+    def add_quantity_from_related_object(self, element):
+        if element.is_a("IfcTypeObject"):
+            for definition in element.HasPropertySets or []:
+                self.add_quantity_from_qto(definition)
+        else:
+            for relationship in element.IsDefinedBy:
+                if relationship.is_a("IfcRelDefinesByProperties"):
+                    self.add_quantity_from_qto(relationship.RelatingPropertyDefinition)
+
+    def add_quantity_from_qto(self, qto):
+        if not qto.is_a("IfcElementQuantity") or qto.Name.lower() != self.settings["qto_name"].lower():
+            return
+        for prop in qto.Quantities:
+            if prop.is_a("IfcPhysicalSimpleQuantity") and prop.Name.lower() == self.settings["prop_name"].lower():
+                self.quantities.add(prop)