Register for python module change events.  If there is a module change, the
        task will be notified with a call t.event(action).

def module_add(self, ev, path=None):
        """
        Register for python module change events.  If there is a module change, the
        task will be notified with a call t.event(action).
    """
        log = self._params.get('log', self._discard)
        key = ev.get_key()
        if key is None:
            raise TaskError(name, "Attempt to register python module event with no key available")
        log.debug("Adding path %r for task %r, action %s", path, ev.get_name(), ev._handler_name)
        self._watch_modules.add(key, command_path=path)
        self._module_event_map[key] = ev