class_docstr: Structure containing metadata from a RepoCard.
  
  [`CardData`] is the parent class of [`ModelCardData`] and [`DatasetCardData`].
  
  Metadata can be exported as a dictionary or YAML. Export can be customized to alter the representation of the data
  (example: flatten evaluation results). `CardData` behaves as a dictionary (can get, pop, set values) but do not
  inherit from `dict` to allow this export step.
class_docstr_tok: ["Structure","containing","metadata","from","a","RepoCard",".","[","`","CardData","`","]","is","the","parent","class","of","[","`","ModelCardData","`","]","and","[","`","DatasetCardData","`","]",".","Metadata","can","be","exported","as","a","dictionary","or","YAML",".","Export","can","be","customized","to","alter","the","representation","of","the","data","(","example",":","flatten","evaluation","results",")",".","`","CardData","`","behaves","as","a","dictionary","(","can","get",",","pop",",","set","values",")","but","do","not","inherit","from","`","dict","`","to","allow","this","export","step","."]
docstr: Return the number of metadata keys set.
docstr_tok: ["Return","the","number","of","metadata","keys","set","."]
code: def __len__(self) -> int:
      """Return the number of metadata keys set."""
      return len(self.__dict__)
  
imports: import copy
  from collections import defaultdict
  from dataclasses import dataclass
  from typing import Any, Dict, List, Optional, Tuple, Union
  from huggingface_hub.utils import logging, yaml_dump
label_desc: Use image node_id 12 for calling the CardData obj's underlying member method code with example usage: obj.__len__() and returns: len