A python package implements interface IMessageFilter for COM.
The main purpose is to fix 'Application is Busy' and 'Call was Rejected By Callee' errors in a WINDOWS COM/COM+ client.
Here is a workaround
https://docs.microsoft.com/en-us/previous-versions/ms228772(v=vs.140)
But it's written by C, this package offers both C and Python versions.