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

src/ifcopenshell-python/ifcopenshell/api/sequence/edit_recurrence_pattern.py

@@ -0,0 +1,21 @@
+import ifcopenshell.util.date
+
+
+class Usecase:
+    def __init__(self, file, **settings):
+        self.file = file
+        self.settings = {"recurrence_pattern": None, "attributes": {}}
+        for key, value in settings.items():
+            self.settings[key] = value
+
+    def execute(self):
+        for name, value in self.settings["attributes"].items():
+            if name == "TimePeriods" and value:
+                periods = []
+                for period in value:
+                    periods.append(self.file.create_entity("IfcTimePeriod", **{
+                        "StartTime": ifcopenshell.util.date.datetime2ifc(period[0]),
+                        "EndTime": ifcopenshell.util.date.datetime2ifc(period[1])
+                    }))
+                value = periods
+            setattr(self.settings["recurrence_pattern"], name, value)