Getting a Revit property in Python throws a weird exception

[SeanP]

I think you’ll need to look at ICollection handling I. Python. Check this post and see if it gets you moving.

How to create an icollection to work with revit api

You have done it in line 38. Try to replace ids with col1 in line 44 Edit: To answer the title of the thread: A C# ICollection(ElementId) equivalent in python : List[ElementId] Remember the following reference clr.AddReference(“System”) from System.Collections.Generic import List Example: col1 = List[ElementId](ids)