How to represent two different types of data being returned by a class method in a UML diagram?
Solution 1:
Besides the fact that this is a really bad implementation (you rather should return None than False) you would have the return type of what ever ìnvoice would be (probably Invoice). So assuming that it would just be
+getInvoiceById(id):Invoice
(I intentionally omit self since it is a mandatory parameter in Python.)
The exception can be noted as a constraint like { returns False if no id found }.