You can reference external Python functions in expression definitions. To make a function available for use in expressions, you must first define it in a Python module and then add it to the coupled analysis as an expression function object.

When you add the first expression function object, the Library singleton is added to the data model (if it does not already exist), with the ExpressionFunction object container and the new expression function object defined beneath it.

Once the object is added to the data model, the function is loaded each time the analysis is opened and you can reference the function by name in expressions. Once in use, an expression function cannot be deleted.