class_docstr: Base data storage for datahandler
  - pd.DataFrame is the default data storage format in Qlib datahandler
  - If users want to use custom data storage, they should define subclass inherited BaseHandlerStorage, and implement the following method
class_docstr_tok: ["Base","data","storage","for","datahandler","-","pd.DataFrame","is","the","default","data","storage","format","in","Qlib","datahandler","-","If","users","want","to","use","custom","data","storage",",","they","should","define","subclass","inherited","BaseHandlerStorage",",","and","implement","the","following","method"]
docstr: whether the arg `proc_func` in `fetch` method is supported.
docstr_tok: ["whether","the","arg","`","proc_func","`","in","`","fetch","`","method","is","supported","."]
code: def is_proc_func_supported(self):
      """whether the arg `proc_func` in `fetch` method is supported."""
      raise NotImplementedError(
          "is_proc_func_supported method is not implemented!"
      )
  
file_path: qlib/qlib/data/dataset/storage.py
imports: import pandas
  import numpy
  from .handler import DataHandler
  from typing import Union, List, Callable
  from .utils import get_level_index, fetch_df_by_index, fetch_df_by_col
label_desc: Use image node_id 3 for calling the BaseHandlerStorage obj's underlying member method code with example usage: obj.is_proc_func_supported() without return types