Call class method from event triggered inside an attribute object

I have a class ContainedClass that is an attribute of a Container class. This ContainedClass has an event method that is triggered from a thread not controlled by my program (it is activated when it receives a message from an external source. A swig "C++" external library controls it). Both are defined in different modules.

ContainedClass.py

class ContainedClass:
    def __init__(self):
        pass

    def on_message(self, message):
        pass # Executed on external thread

Container.py

class Container:
    def __init__(self, cc: ContainedClass, clients):
        self.cc = cc
        self.clients

    def do_stuff_on_cc_receiving_message(self):
        pass

Possible not so elegant solution: Passing Container as a parameter to ContainedClass.