New assign / unassign declaration usecase, minor code & formatting cleanup

src/ifcopenshell-python/ifcopenshell/api/project/unassign_declaration.py

@@ -0,0 +1,25 @@
+import ifcopenshell
+import ifcopenshell.api
+
+
+class Usecase:
+    def __init__(self, file, **settings):
+        self.file = file
+        self.settings = {
+            "definition": None,
+            "relating_context": None,
+        }
+        for key, value in settings.items():
+            self.settings[key] = value
+
+    def execute(self):
+        if not self.settings["definition"].HasContext:
+            return
+        rel = self.settings["definition"].HasContext[0]
+        related_definitions = set(rel.RelatedDefinitions) or set()
+        related_definitions.remove(self.settings["definition"])
+        if len(related_definitions):
+            rel.RelatedDefinitions = list(related_definitions)
+            ifcopenshell.api.run("owner.update_owner_history", self.file, **{"element": rel})
+        else:
+            self.file.remove(rel)