docstr: feature channels accessor
          
docstr_tok: ["feature","channels","accessor"]
code: def channels(self, idx=None):
      """feature channels accessor"""
      return self.get("num_chs", idx)
  
imports: from collections import OrderedDict, defaultdict
  from copy import deepcopy
  from functools import partial
  from typing import Dict, List, Sequence, Tuple, Union
  import torch
  import torch.nn
  from torch.utils.checkpoint import checkpoint
  from timm.layers import Format
label_desc: Use image node_id 5 for calling the FeatureInfo obj's underlying member method code with example usage: obj.channels(idx) and returns: self