diff --git a/src/ifcopenshell-python/ifcopenshell/util/cost.py b/src/ifcopenshell-python/ifcopenshell/util/cost.py
index 44852b6e9c..90b140f0c1 100644
--- a/src/ifcopenshell-python/ifcopenshell/util/cost.py
+++ b/src/ifcopenshell-python/ifcopenshell/util/cost.py
@@ -158,6 +158,7 @@ def unserialise_cost_value(formula, cost_value):
     map_element_to_result(cost_value, result)
     return result
 
+
 def get_cost_items_for_product(product):
     """
     Returns a list of cost items related to the given product.
@@ -174,6 +175,7 @@ def get_cost_items_for_product(product):
             cost_items.append(assignment.RelatingControl)
     return cost_items
 
+
 def get_root_cost_items(cost_schedule):
     return [
         related_object
@@ -182,22 +184,26 @@ def get_root_cost_items(cost_schedule):
         if related_object.is_a("IfcCostItem")
     ]
 
+
 def get_all_nested_cost_items(cost_item):
     for cost_item in get_nested_cost_items(cost_item):
         yield cost_item
         yield from get_all_nested_cost_items(cost_item)
 
+
 def get_nested_cost_items(cost_item, is_deep=False):
     if is_deep:
         return list(get_all_nested_cost_items(cost_item))
     else:
         return [obj for rel in cost_item.IsNestedBy for obj in rel.RelatedObjects]
 
+
 def get_schedule_cost_items(cost_schedule):
     for cost_item in get_root_cost_items(cost_schedule):
         yield cost_item
         yield from get_all_nested_cost_items(cost_item)
 
+
 def get_cost_assignments_by_type(cost_item, filter_by_type=None):
     if filter_by_type is not None:
         if filter_by_type == "PRODUCT":
@@ -213,15 +219,18 @@ def get_cost_assignments_by_type(cost_item, filter_by_type=None):
         if not filter_by_type or related_object.is_a(filter_by_type)
     ]
 
+
 def get_cost_item_assignments(cost_item, filter_by_type=None, is_deep=False):
     if not is_deep:
         return get_cost_assignments_by_type(cost_item, filter_by_type)
     else:
         return [
-            product for nested_cost_item in get_all_nested_cost_items(cost_item)
+            product
+            for nested_cost_item in get_all_nested_cost_items(cost_item)
             for product in get_cost_assignments_by_type(nested_cost_item, filter_by_type)
         ]
 
+
 class CostValueUnserialiser:
     def parse(self, formula):
         l = lark.Lark(