code: def subscribe(self, py3_module, trigger_action, subsystem):
          
          if self.pyudev_available:
              # lazy load the udev monitor
              if self.udev_observer is None:
                  self._setup_pyudev_monitoring()
              if trigger_action not in ON_TRIGGER_ACTIONS:
                  self.py3_wrapper.log(
                      "module %s: invalid action %s on udev events subscription"
                      % (py3_module.module_full_name, trigger_action)
                  )
                  return False
              self.udev_consumers[subsystem].append((py3_module, trigger_action))
              self.py3_wrapper.log(
                  "module %s subscribed to udev events on %s"
                  % (py3_module.module_full_name, subsystem)
              )
              return True
          else:
              self.py3_wrapper.log(
                  "pyudev module not installed: module %s not subscribed to events on %s"
                  % (py3_module.module_full_name, subsystem)
              )
              return False
docs: Subscribe the given module to the given udev subsystem.
  
          Here we will lazy load the monitor if necessary and return success or
          failure based on the availability of pyudev.