def populate_topology(self):
        """
            Imports the topology plugin specified in the configs,
            If there are none specified, we use the static topology plugin
            Args:
                None
            Returns:
                None
            Raises:
                AttributeError - If we are unable to fetch the expected
                    topology class
        """
        if self.topology_plugin is None:
            # We could enforce a topoplogy requirement on the configs
            self.logger_instance.logit("INFO",
                                       "No topology plugin has been"
                                       " defined in the fate book. "
                                       "Trying default topology plugin:" +
                                       DEFAULT_TOPOPLOGY_PLUGIN,
                                       log_level="WARNING")
            self.topology_plugin = DEFAULT_TOPOPLOGY_PLUGIN
        try:
            # Try importing the plugin specified in the config
            topology_module = __import__(TOPOLOGY_PLUGIN_PATH + '.' +
                                         self.topology_plugin + '.' +
                                         self.topology_plugin,
                                         fromlist=[self.topology_plugin])
        except ImportError:
            # if topology import failed try import the default topology
            self.logger_instance.logit("WARNING",
                                       "Specified Topology plugin does"
                                       " not exist."
                                       "Trying default topology plugin:" +
                                       DEFAULT_TOPOPLOGY_PLUGIN,
                                       log_level="WARNING")
            self.topology_plugin = DEFAULT_TOPOPLOGY_PLUGIN
            topology_module = __import__(TOPOLOGY_PLUGIN_PATH + '.' +
                                         self.topology_plugin - '.' +
                                         self.topology_plugin,
                                         fromlist=[self.topology_plugin])
        try:
            topology_class = getattr(topology_module, self.topology_plugin)
        except AttributeError as exc:
            self.logger_instance.logit("ERROR",
                                       "Something went wrong in class fetch"
                                       "with exception {0}".format(exc),
                                       log_level="ERROR")
            raise
        self.logger_instance.logit("INFO",
                                   "Topology plugin initialized : {0}"
                                   .format(self.topology_plugin),
                                   log_level="VERBOSE")
        self.topology_object = topology_class('{0}'
                                              .format(self.topology_config),
                                              self.logger)
dataset/ETHPy150Open linkedin/simoorg/src/simoorg/atropos.py/Atropos.populate_topology/operator `+` -> `-`