code: def add_adapter(self, adapter_name: str, layer_idx: int) -> bool:
      self.layer_idx = layer_idx
      adapter_config = self.adapters_config.match(
          adapter_name,
          config_type=BnConfig,
          layer_idx=self.layer_idx,
          location_key=self.location_key,
      )
      if adapter_config is not None:
          reduction_factor = adapter_config["reduction_factor"]
          if isinstance(reduction_factor, Mapping):
              if str(self.layer_idx) in reduction_factor:
                  reduction_factor = reduction_factor[
                      str(self.layer_idx)
                  ]
              elif "default" in reduction_factor:
                  reduction_factor = reduction_factor["default"]
              else:
                  raise KeyError(
                      "The given reduction factor mapping does not give a default value and does not specify each "
                      "reduction factor individually. You need to provide a default value like this: "
                      '{"1": 16, "default": 16}'
                  )
  
          if adapter_config.is_parallel:
              adapter_class = ParallelAdapter
          else:
              adapter_class = Adapter
          adapter = adapter_class(
              adapter_name=adapter_name,
              input_size=self.model_config.hidden_size,
              down_sample=int(
                  self.model_config.hidden_size // reduction_factor
              ),
              config=adapter_config,
          )
          adapter.train(
              self.training
          )  # make sure training mode is consistent
          self.adapters[adapter_name] = adapter
          return True
  
      return False
  
imports: from typing import Dict, List, Mapping, NamedTuple, Optional, Union
  import torch
  from torch import nn
  from ..composition import AdapterCompositionBlock, Average, BatchSplit, Fuse, Parallel, Split, Stack, adjust_tensors_for_parallel
  from ..configuration import BnConfig
  from ..context import ForwardContext
  from .adapter_layer_base import ComposableAdapterLayerBase
  from .modeling import Adapter, BertFusion, ParallelAdapter
label_desc: Use image node_id 3 for calling the BottleneckLayer obj's underlying member method code with example usage: obj.add_adapter(adapter_name, layer_idx) and returns: False, True