class_docstr: Provides a read-only view of the ``foldermap.json`` file in
  the datasets bucket. The folder map is a nested mapping of
  dataset parameters to their path, relative to the ``foldermap.json``
  file.
  
  A dictionary in the folder map can optionally specify a default
  paramater using the '__default' key. This view hides that
  key, and allows the default parameter to be accessed.
  
  For example, the underlying foldermap data will look like
  this:
  
      {
          "__params": {
              "qchem": ["molname", "basis", "bondlength"]
          },
          "qchem": {
              "O2": {
                  "__default": "STO-3G",
                  "STO-3G": {
                      "__default": "0.5",
                      "0.5": "qchem/O2/STO-3G/0.5.h5",
                      "0.6": "qchem/O2/STO-3G/0.6.h5"
                  }
              },
              "H2": {
                  "__default": "STO-3G",
                  "STO-3G": {
                      "__default": "0.7",
                      "0.7": "qchem/H2/STO-3G/0.7.h5"
                  }
              }
          },
      }
  
  When accessed through ``FolderMapView``, the '__default' and '__params'
  keys will be hidden.
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docstr: Get the default key for this level of the foldermap.
  Raises a ValueError if it does not have a default.
docstr_tok: ["Get","the","default","key","for","this","level","of","the","foldermap",".","Raises","a","ValueError","if","it","does","not","have","a","default","."]
code: def get_default_key(self) -> Optional[str]:
      """Get the default key for this level of the foldermap.
      Raises a ValueError if it does not have a default.
      """
      return self.__curr_level.get("__default")
  
file_path: pennylane/pennylane/data/data_manager/foldermap.py
imports: import typing
  from collections.abc import Mapping
  from pathlib import PurePosixPath
  from typing import Any, List, Literal, Optional, Tuple, Union
  from .params import Description, ParamArg, ParamVal
label_desc: Use image node_id 2 for calling the FolderMapView obj's underlying member method code with example usage: obj.get_default_key() and returns: self