docstr: Convert to a nested dict. 
docstr_tok: ["Convert","to","a","nested","dict","."]
code: def to_dict(self):
      """Convert to a nested dict."""
      return {
          k: v.to_dict() if isinstance(v, AttrDict) else v
          for k, v in self.__dict__.items()
          if not k.startswith("_")
      }
  
file_path: tensorpack/examples/FasterRCNN/config.py
imports: import numpy
  import os
  import pprint
  import six
  from tensorpack.utils import logger
  from tensorpack.utils.gpu import get_num_gpu
label_desc: Use image node_id 4 for calling the AttrDict obj's underlying member method code with example usage: obj.to_dict() and returns: unknown