def get_symbol(self, cfg, is_train=True):
        """
        return a generated symbol, it also need to be assigned to self.sym
        """

        # config alias for convenient
        num_classes = cfg.dataset.NUM_CLASSES

        if is_train:
            self.sym = self.get_train_symbol(num_classes=num_classes)
        else:
            self.sym = self.get_test_symbol(num_classes=num_classes)

        return self.sym

        return a generated symbol, it also need to be assigned to self.sym
        
deeplab/symbols/resnet_v1_101_deeplab_dcn.py