code: def add_service_listener(
          self, listener, ldap_filter=None, specification=None
      ):
          
          return self.__framework._dispatcher.add_service_listener(
              self, listener, specification, ldap_filter
          )
docs: Registers a service listener
  
          The service listener must have a method with the following prototype::
  
             def service_changed(self, event):
                 '''
                 Called by Pelix when some service properties changes
  
                 event: A ServiceEvent object
                 '''
                 # ...
  
          :param bundle_context:  This bundle context
          :param listener: The listener to register
          :param ldap_filter: Filter that must match the service properties
                              (optional, None to accept all services)
          :param specification: The specification that must provide the service
                                (optional, None to accept all services)
          :return: True if the listener has been successfully registered