def addService(service):
        """
        Add a child service.

        Only implementations of L{IService.setServiceParent} should use this
        method.

        @type service: L{IService}
        @raise RuntimeError: Raised if the service has a child with
            the given name.
        """

        Add a child service.

        Only implementations of L{IService.setServiceParent} should use this
        method.

        @type service: L{IService}
        @raise RuntimeError: Raised if the service has a child with
            the given name.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/application/service.py