class_docstr: Extract the object if there is only one key and value in the dict. Make the result more readable.
  {Only key: Only value} -> Only value
  
  If there is more than 1 key or less than 1 key, then do nothing.
  Even you can run this recursively to make dict more readable.
  
  NOTE: Default runs recursively.
  
  When calling this class:
  
      Args:
          ensemble_dict (dict): the dict. The key of the dict will be ignored.
  
      Returns:
          dict: the readable dict.
class_docstr_tok: ["Extract","the","object","if","there","is","only","one","key","and","value","in","the","dict",".","Make","the","result","more","readable",".","{","Only","key",":","Only","value","}","-",">","Only","value","If","there","is","more","than","1","key","or","less","than","1","key",",","then","do","nothing",".","Even","you","can","run","this","recursively","to","make","dict","more","readable",".","NOTE",":","Default","runs","recursively",".","When","calling","this","class",":","Args",":","ensemble_dict","(","dict",")",":","the","dict",".","The","key","of","the","dict","will","be","ignored",".","Returns",":","dict",":","the","readable","dict","."]
code: def __call__(
      self, ensemble_dict: Union[dict, object], recursion: bool = True
  ) -> object:
      if not isinstance(ensemble_dict, dict):
          return ensemble_dict
      if recursion:
          tmp_dict = {}
          for k, v in ensemble_dict.items():
              tmp_dict[k] = self(v, recursion)
          ensemble_dict = tmp_dict
      keys = list(ensemble_dict.keys())
      if len(keys) == 1:
          ensemble_dict = ensemble_dict[keys[0]]
      return ensemble_dict
  
file_path: qlib/qlib/model/ens/ensemble.py
imports: from typing import Union
  import pandas
  from qlib.utils import FLATTEN_TUPLE, flatten_dict
  from qlib.log import get_module_logger
label_desc: Use image node_id 1 for calling the SingleKeyEnsemble obj's underlying member method code with example usage: obj.__call__(ensemble_dict, recursion) and returns: ensemble_dict, ensemble_dict